A Quarterly Publication of
The Smith-Kettlewell Eye Research Institute’s
Rehabilitation Engineering Research Center
William Gerrey, Editor
Original support provided by:
The Smith-Kettlewell Eye Research Institute
and the National Institute on Disability and Rehabilitation Research
Note: This archive is provided as a historical resource. Details regarding products, suppliers, and other contact information are original and may be outdated.
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TABLE OF CONTENTS
In this installment, building of a "continuity
tester" will be described. It is the first instrument in this
series which will be fitted into a box. Methods of drilling
speaker holes and securing things will be entertained.
This circuit has appeared in SKTF before. If you do not
have such an instrument yet, shame on you! Without it, you
cannot tell which way diodes are facing (or many electrolytic
capacitors, either). Without it, you will have to ask a sighted
friend which lead is which on battery clips (they being color-coded black and red). Without it, you will not be able to discriminate between the various resistors that you have bought for
a project. (You cannot identify resistors, exactly, with this
instrument; but you can, knowing what you have in your collection, figure out which ones are which.) Without it, you cannot
identify the terminals on mini phone jacks. Without it, checking
your wiring of other projects is much less certain. Without it,
you cannot test cables and patch cords. Build this one thing, at
(It's only fair to tell you that this identical device is
commercially available from Science Products (formerly Science
for the Blind), 1043 Lancaster Ave., Berwyn, PA 19312; phone,
(215) 296-2111. It is sold under the name of "Audicator.")
Future installments of this series will rely heavily on use
of this particular continuity tester (its only partial substitute
being pretty good vision). In the last installment, you will
perhaps recall the pointed question, "How can you read the color
codes on the parts?" "This instrument, that's how," is the
There are other commercial audible continuity testers on the
market -- Radio Shack sells one. However, only one I have seen
(and it was quite expensive) gives any indication about the
resistance being tested. Without this feature, all you can check
with them is the polarity of garden-variety diodes, battery
clips, and open circuits -- only half the job. [Our deaf-blind
readers should not feel left out; the article "Continuity Testers
-- Old and New" (SKTF, Fall 1982) describes a circuit using a 555
"timer chip" which can deliver enough power for good tactual
indication, provided the frequency range is lowered.]
Let's review the rules of the "point-to-point wiring game"
-- the abbreviated set:
- We have to choose the size of board. (In this case, this
will be given, since the size of the box that contains the
project fixes this size.)
- All components are inserted from, and rest on, the
"component side" of the board. Even wires from the battery are
inserted from this side-the top side. Interconnection of the
parts is all done on the "wiring side" of the board-the bottom
- Very little, if any, extra wire should be necessary (with
the exception of supply busses). Placement of the items should
be done so that components' leads will be the main source of
- Components should not have to reach over each other; give
them a space of their own, where they can rest in comfort.
- Where possible, components shall not be placed at odd
angles; they should be fitted into a straight row or column of
- All of these rules are to be broken "for cause"; none
should be held binding where compromise would make more sense, or
wherever critical electrical place ment makes compromise necessary.
You get the advantage of having a physical design that was
arrived at through several months of work in our training program. A good cabinet has been chosen -- the Radio Shack No.
270-221, measuring 4.4 inches by 2.44 inches by 1.06 inches. A
board that is 2.2 inches wide and 3 inches long covers most of
the bottom of the box, leaving room beyond one end for the 9-volt
battery to stand up on edge. All of the components (with the
exception of the test lead jack) are mounted on the component
side of the board; even the speaker is cemented face down on the
board, where it speaks through the perforations. Yet, with all
its refinement, this design is not completely free of rule breaking, as you will see.
Know Your Parts
The following items are to be procured:
- 1--Small cabinet, Radio Shack 270-221.
- 1--Large slab of perforated board with a nonstaggered hole
pattern and with a spacing between centers of 0.1 inch, Radio
Shack 276-1396, or Vector Electronics No. 169P47EP.
- 1--Small speaker, Radio Shack 40-245. (This is actually a
bit too large, a 2-inch diameter causing cramped conditions on
the board. If you have another supplier than Radio Shack, try to
get a 1-1/2 inch speaker.)
- 1--Push-pull output transformer, Radio Shack 273-1380 (500
or 1000 ohm center-tapped primary, and "voice-coil" secondary).
- 1--PNP silicon transistor, type 2N2905, 2N2907, or Radio
- 1--0.1uF mylar or disc ceramic capacitor, 30 volts.
- 1--4.7K ohm resistor, 1/4 or 1/2 watt.
- 1--Set of snaps for a 9-volt battery. (Buy a whole packet of
these; since the wire on them is usually inferior, you may use
two or three in successfully attaching one.)
- 1--Mini phone jack, open circuit. (Closed-circuit will do,
but we must then figure out which is the "switch terminal" in
order to ignore it.)
- 1--Mini phone plug; unshielded will do.
- 1--Alligator clip lead to cut in two, preferably eighteen inches or longer.
- Some--Stranded hookup wire, 20-gauge. (Black is fine with
me, how about you?)
Which Part is Which
Now is when you could really use some
background in "electronics theory." In the training program, it
is our experience that, if students tend to forget (or loosely
associate) terms like "transformer," "transistor," "resistor,"
and the like, instructions on putting them together come hard.
Take an hour or two of drill, review your tape (or notes) on
seeing electronic parts, and become familiar with the following:
A jack is a thing that you plug a plug into; the plug is the
male item that plugs into the jack. The resistor is a little
round capsule with a lead coming out each end. A transistor is a
device with three leads (think three!); these leads are called
the emitter, the base, and the collector. A transformer is
large, even in the best of cases; it has "windings" around some
sort of magnetic core. The capacitor in this project may take
several shapes. If it is disc ceramic, it will look like a disc
with leads emerging from one edge. If it is mylar, it may either
have "radial leads" or "axial leads." If it is mylar with radial
leads, it will look like a piece of candy with leads out the
bottom. If it has axial leads, it will look like the resistor,
except that its diameter will be larger.
Plugs, jacks, and speakers usually have terminals called
"solder lugs" to which hookup wire is attached. Most often,
solder lugs are small metal tabs that have holes into which wire
can be inserted -- then bent double and squeezed tightly about
the lug with needle-nosed pliers. (In the old days, the practice
was to insert the wire, and then wrap the wire around the lug.
This practice caused more trouble than it was worth, especially
The transistor you buy may be in one of a few different
configurations. For example, an odd-ball package might be a
half-round plastic unit with the three leads "in line" (in a row
adjacent to the flat side); usually, with the leads pointing
upward and the flat side away from you, the three leads -- from
left to right -- are: emitter, base, collector. The more usual
transistor has the leads arranged in an isosceles triangle, as
Most commonly, the leads of a small-signal transistor are at
the vertices of a triangle, this triangle having a long base and
two short sides. With the leads pointing upward and the long
side of the triangle toward you, the lower left corner lead is
the emitter, the one in the middle at the top is the base, and
the one at the lower right corner is the collector. Also, quite
commonly the emitter lead is marked on the case -- there will be
a small protruding tab (or, in some cases, a flat side on the
package) immediately below and adjacent to the emitter.
The transformer has a bobbin of windings around the center
post of an iron frame, this frame encircling the bobbin on two
sides as well. Two leads emerge out from under one edge of the
bobbin on one side of the iron frame; these are the leads to the
"secondary winding." On the other side of the frame, three leads
emerge; these are leads to the ends of the "primary winding,"
plus a "center tap" on this winding. Usually, the center tap is
the middle lead (although this needn't be the case, since they
are color-coded as well). Sometimes, the secondary has a tap or
two for different impedances; an ohmmeter is required if the
blind person is to identify which winding is which, in that case.
Usually, on the corners of the frame adjacent to these two
sets of leads, there are metal mounting tabs by which the heavy
transformer is secured to its mounting surface. For large transformers, these tabs contain screw holes; on this miniature unit,
the tabs are meant to solder into a PC board. On perforated
board, holes are enlarged to accept the tabs, whereupon they are
bent outward against the "wiring side" of the board.
Presenting the Circuit, Irrespective of Layout
(Note: For the theory of operation of this circuit, see
"Continuity Tester Circuits, Old and New," SKTF, Fall 1982 -- the
particular circuit being called "Transistor Blocking
In Part I of this series, I did something I will rarely, if
ever, do again; I described the layout of a circuit in pictorial
terms, and followed this with the circuit. No more free rides
for you; this time, the presentation will be in the proper order
-- circuit diagram first! Someday soon, the "circuit" will
interest you most. Any palaver about where some guy placed the
parts will be of more casual interest -- "Hum, that's how he did
As you read this -- two or three times -- try to arrive at
your own ideas of placement. You know the shapes of the parts:
the transformer has three leads of immediate interest out one
side, the transistor is a three-legged stool whose "legs" are in
an order you have memorized (emitter, base, collector), and the
capacitor is a "coupling device" which would logically fit in
between its appointed connections. Forget about the size constraints of the board, for the moment; picture these items lying
on their backs on the table in front of you, and how they might
be connected together in the middle of a circuit board as big as
The centertap of the transformer's
primary goes to the emitter of a transistor. The collector of
this transistor goes to the negative side of the 9-volt battery
and is taken as ground. One end of the primary winding goes
through 0.1uF to the base of the transistor, while the other end
of the primary goes to plus 9 volts.
The sleeve of the test-lead jack (and hence, the negative
test lead) is grounded. The tip contact of this jack (and hence,
the positive test lead) goes through 4.7K to the transistor base.
The transformer secondary goes to the speaker. This completes the circuit.
I don't care, at this stage, what your mental image of the
physical arrangement is. I do, however, want you to refine this
image, based on the very specific construction procedures given
in the next section. When you've finished building the instrument, come back and re-read this circuit to see if it doesn't
play a familiar tune.
It's only fair to mention here that the "Hints and Kinks"
section contains ideas you will want. Rather than mindlessly
following these instructions, only to read on and scream "Now you
tell me!," I recommend that you read this section, then go on to
"Hints and Kinks," and then come back to the construction business. Also, this paper ends with a discourse called "Commiserations" which may cheer you up as frustrations mount; you have my
permission to read this first, as well.
First, you need a piece of perforated board of the prescribed dimensions -- 2.2 inches by 3 inches. As per the procedure in the "Hints and Kinks" section of Part I, "knock off" such
a piece. (I counted 21 holes in from one edge of my large piece,
lined this up with the edge of my clamp, then scribed and broke
the board along its full width. Then, I counted 29 holes away
from one end of the long strip I had made, and made another break
If you have the recommended piece of Radio Shack board, it
will be too long for many clamping arrangements. It is possible,
with care, to make a partial break -- as long as the clamp is
wide -- then move the board along and finish the job. Another
way, of course, is to make a saw cut into the board so that a
tongue-like section the width of the clamp is available. Don't,
for heaven's sake, worry about having oddly shaped pieces left
over; you'll use these in oddly conceived projects.
Mounting the Transformer
In order to fit the mounting
tabs through the board, it is necessary to enlarge holes to
accommodate them. For this purpose, I used a No. 44 drill bit in
a hand drill (electric is fine -- doesn't take very long, that's
for sure). In the case of this transformer, the tabs are 0.8
inches apart. Therefore, I drilled out the following holes:
Picture the board from the component side with the short
dimension toward you (its length being perpendicular to the edge
of the table). The nearest two-thirds of the board will eventually have the speaker glued on it, and will be left blank, as far
as circuitry is concerned. The transformer is placed near the
upper right corner -- its three primary leads pointing to the
left. In a column of holes, four in from the right-hand long
edge, I drilled out the second hole down from the top, and the
tenth one down from the top. Fit the transformer's tabs into
these holes, being careful not to trap any leads under it; turn
the board over and bend the tabs outward with a screwdriver.
What would you do if your transformer were 0.75 inches wide
and didn't match the holes? Well then, feeling for holes with
its tabs, turn it until you find a likely match. You heard me,
mount it askew, thus violating Rule 5.
Inserting the Transistor
You are indeed lucky if your
transistor is a 2N2905; the leads emerging from this unit (a TO5
package) match up with holes in this pattern of board. Those of
us with 2N2907's and 276-2023's have a problem; these leads are
too close together. Leads of smaller transistors have to be
fanned out into a slightly larger triangular pattern. This also
means that the small units cannot be pulled down properly against
the component side of the board. (Any attempt to force them down
against the board will cause leads to short out against the rim
of their metal can.) Students of the Wiring Game should take
note that this must constitute a minor violation of some kind --
perhaps bending Rules 2, 4, and 5.
There seems to be a certain logic in putting the transistor
adjacent to the leads of the primary winding; we'll orient it so
that its emitter pretty much lines up with the center tap.
Therefore, the collector and emitter leads will go into holes in
the fifth row from the top (the board being oriented as before,
with the transformer at the upper-right corner).
Note that, with the leads of the transistor pointing
straight down (and the tab being at the lower right), the order
is, from left to right: collector, base, emitter. The collector
will go into the fifth from the top and sixth from the left; the
base will be in the fourth from the top and seventh from the
left; the emitter will go in the fifth from the top and the
eighth from the left.
Once through, bend the emitter lead in the direction of the
transformer. For reasons that will soon become apparent, bend
the base lead straight up toward its edge of the board. Bend the
collector lead toward you. Rocking the transistor in various
directions (so as to encourage each lead to lift off the wiring
side of the board), bend them all firmly down against the wiring
Without cutting it short, poke the center tap lead down near
the emitter lead -- say, the fourth row down and ten from the
left. Bend its tinned end down over the emitter lead and solder
Students of the Wiring Game might think that this lead
should be cut short so as not to leave a big loop on top of the
board. Not so. In the first place, this lead has been nicely
tinned by the factory; why mess it up. In the second place, if
you ever salvage parts from this project (or repair it), you'll
thank yourself for retaining this lead's length; such a loop is
actually called a "courtesy lead." Thirdly, the connection will
stay in place while you're soldering if you put the loop to good
use; clip it down against the edge of the board with an alligator
clip, thus keeping the elusive little blighter in a stable position.
Installing the Capacitor
It makes good sense to put the
0.1uF capacitor near the top edge of the board, between the
transformer and the transistor's base lead. Let's put it into
holes in the second row from the top. The distance between its
leads depends on what kind you've got. Mine happens to be a
fairly large one, so its leads end up in the eighth and thirteenth from the left.
Bend the two capacitor leads straight to the sides. One
will cross the base lead, to which it is then soldered. The
other awaits a transformer lead. You can plug the transformer
lead into any hole to the right of the capacitor -- in the third
row down. (Mine is in the third down and the fourteenth from the
left.) Bend its tinned end down so as to cross the capacitor
lead and solder it there.
As soon as this latter transformer lead has been soldered,
cut off any excess capacitor lead that reaches under the transformer. Do not, for a reason to be seen, cut the capacitor's
other lead after it crosses the base.
Placing the Resistor
I placed a nice large 1/2-watt unit
in a column near the edge of the board. First, bend the resistor's leads at right angles to its body; its body will ly flat on
the board when it is installed. In the case of my 1/2-watt unit,
the top lead goes into the top row and third from the left; its
bottom is in the sixth down and third from the left. Use of a
1/4-watt resistor would put its lower lead in the fifth hole
Cut the upper resistor lead so that it protrudes only about
one-fourth inch; bend it over across the capacitor lead and
solder it there. Why cut the lead? Well, if you don't, you'll
stand a fair chance of soldering it to its other lead farther
down in the column, that's why.
Installing the Battery Snaps
Now, if you had a continuity
tester, you could tell which lead is the positive and which is
negative. This is done by clipping one of your future tester's
leads to a snap -- say, for example, the small snap, which is the
negative -- then touching the wires with the other test lead
until you find the one that beeps. For now, however, I guess
you're stuck with getting sighted help.
Poke the black lead (the negative) into the board on the
transformer side of the transistor's collector lead -- say, six
down and seven to the right. Bend it over to cross the collector
and solder it there. Somewhere near the lower portion of the
transformer's frame, poke the remaining primary lead and the red
battery lead into holes next to each other; solder them together
on the wiring side of the board. (Do this high enough up so as
to leave room for the speaker.)
The above two connections sound easy. Actually, because of
the wire sizes (smaller than I care to mess with), these procedures are tricky. You may need to strip additional insulation
and re-tin the wires, especially on the battery leads. (Try to
leave the transformer lead alone; if you break it, you'll have to
replace this item.) When you do get the tinned ends to meet,
their ephemeral ends will not stay in contact unless their insulated portions are held for stability. They can be wrapped
around the capacitor, for example, or they can be clipped to the
edge of the board in the jaws of an alligator clip.
Eventually, the test lead jack will
be tethered to the board by two 5-inch lengths of hookup wire.
For the moment, however, I have a trick for you. Let us install
a 10-inch loop of wire between the desired connection points on
the board. We'll cut this loop and insert the jack later, after
we know that the tester works. In this way, our continuity
tester will test itself with this "short circuit" we have provided.
Strip and tin the ends of a 10- or 12-inch piece of stranded
hookup wire. Plug one end into a hole next to the collector,
perhaps seven down and five from the left; bend this over so as
to cross the collector and solder it. Plug in the other end near
the edge of the board, so that it can be attached to the free end
of the resistor -- say, seven down and the second column from the
Installing the Speaker
Eventually, the speaker will be
glued to the board on the component side. It may seem like a
good idea to do this first, then connect it up; this would tend
to establish a stable situation. On the other hand, I prefer to
make these connections first; I find it appealing to have the
freedom of orienting the speaker so that each terminal, in turn,
However you decide to do it, the idea is to put the tinned
end of each wire through the hole in its respective lug, bend it
double -- firmly -- and solder it. Naturally, the two secondary
leads go to the two lugs on the speaker.
At this point, we should be able to
find out if this project works. Connect a 9-volt battery to the
snaps; the instrument should emit a high steady beep. If this
beep is not steady, you have a bad solder connection. If it
doesn't beep at all, there could be one of the following reasons:
The wiring could be correct, but with a connection or two
not being completed. Wiggle and jiggle each connection and
As far as incorrect wiring is concerned, the most likely
suspects are: reversal of the battery wires, having the center
tap exchanged with one end of the primary, or having inserted the
transistor incorrectly (turned 60 degrees).
In order to change anything, reheat the offending connection
and pull on one of the parts. Whatever you pull on can be extracted from the board in this way. Before frustration overtakes
you, go have a cup of tea, and read the final section here called
Wiring the Jack
After the oscillator has proven itself,
you can use it to show you how the jack is to be wired. First,
it would be good to discuss the plug and the jack, and to brace
yourself for the variations you might encounter.
If the jack you have is of the "open-circuit type," it will
have two terminal lugs -- plus the springy contact that meets the
tip of the plug; once you have identified either one of these,
belonging either to the tip contact or the sleeve, you are set.
The plot gets thicker when you have a "closed-circuit" version;
an extra contact senses when the tip contact has been forced
aside by the plug. With closed-circuit jacks, the sleeve is easy
to identify with your tester, but the other two lugs look the
same electrically until a plug has been inserted. The way to
distinguish between the "tip" and the "switch" is via the plug,
which is described below:
The "handle" of the plug, called the "connector shell," can
be unscrewed. Inside, you will see a short stubby solder lug
(which goes to the tip) and a longer stave-like metal strip with
a solder-lug hole halfway along it and a cable clamp on the end.
Given the cable clamp, it makes sense that this latter item is a
connection to the sleeve of the plug (this sleeve usually going
to the shield of a cable).
With the plug inserted into the jack, the tester will indicate when there is "continuity" between the cable clamp and one
of the lugs on the jack (the lug intended for connection to the
sleeve). By the same token, continuity will be seen between the
plug's and jack's tip connections. Of course, this procedure
will work with the open-circuit jack, but it is not necessary to
utilize the plug; you need only touch one test lead to the body
(actual sleeve) of the jack, fishing around with the other until
a beep indicates that you've found its lug; the remaining lug is
for the tip contact.
Going back to the circuit board, cut the 10-inch loop of
test-lead wire in half. Strip and tin these ends. Connect the
battery, and your tester is ready for business (it should not
beep when these leads are separated).
Hold one of your tester's leads against the body of the
jack; fish for the lug that beeps with the other tester wire.
This lug is the sleeve connection; solder it to the wire that
comes from the transistor collector. With your alligator clip
lead, short out the plug -- clipping one end onto the short lug,
and the other onto the cable clamp. Insert this shorted plug.
With the remaining tester lead, fish for the lug on the jack that
makes the tester beep. Solder this wire, which should be the one
coming from the 4.7K resistor, to this lug.
Preparing the Test Leads
While the soldering iron is hot,
we might as well do this now, even though it could very well be
left 'til later. Cut your alligator clip lead in two; strip and
tin the ends. If you have a piece of spaghetti tubing, pass one
of the leads through it (to mark it as "positive"); if not spaghetti, wrap it in a small bit of tape directly behind the alligator clip. Pass these leads down through the cover of the plug,
before you forget to do so.
Insert the marked "positive" lead through the hole in the
"tip" lug and solder it. Pass the "negative" (unmarked) test
lead through the hole in the longer sleeve terminal; make this
insertion from inside out -- inserting just above the positive
lug. You'll have to make three-quarters of a turn around this
member with the tinned end because of the "stave-like" shape of
it. Solder this lead as well.
Cut off any excess wire, and tentatively screw down the
cover over these connections. With the clips separated, plug
this assembly into the jack; it should not make the tester beep
(if it does, the plug is shorted). Touching the clips together
should make the tester beep. If so, tighten the cover as best
you can with your fingers, and congratulations, you've done
It would be nice if the cable clamp could be used to take
stress off these connections. You can try wrapping the wires in
a bit of tape immediately above the solder connections -- then
squeezing the cable clamp around this assembly with needle-nosed
pliers. Usually, however, the cable clamp is far too small to do
any good; students here usually just forget about it.
If you haven't already done so, glue
the speaker in place. Since the board is porous and the rim
around the speaker cone is cardboard, white glue or animal glue
will be sufficient in this case (this is usually not true). Make
sure that the speaker is confined to the boundaries of the board
-- otherwise, the board will not rest properly in the box, or
there will be insufficient room for the battery.
Now it is time to ravage the box. Whether done randomly or
by one of the methods described in "Hints and Kinks," drill some
speaker holes in the bottom of the box, centering them at a
distance of about 2-1/8 inches from the "battery end." Next, lay
the board in the box with the speaker nearest the battery end,
and find a nice clear spot for the jack. (I put mine on the
opposite side from the transformer, drilling its hole 2-5/8
inches from the battery end, and 5/8 of an inch up from the
bottom.) There are lots of places where you cannot put the jack;
you cannot place it where it will interfere with installation of
the battery, or where it will run into the transformer.
As far as drill sizes are concerned, I use a No. 43 for the
speaker holes. In drilling for the jack, which requires a 1/4inch hole, I first use the No. 43 to make a pilot hole, then go
to the No. 1 bit for enlarging it.
In drilling for the jack, your intention should also be to
miss those pesky ribs inside the box (which are intended for
holding circuit boards on edge). If your hole came too close to
one of these ribs, so that the jack cannot rest comfortably as
the nut is tightened, it is easy to remove the offending ribs.
The Lexan out of which the cabinet is made is very soft. With a
sharp knife, for example, you can calmly "pare" the ribs completely off. Another way is to nip them off with diagonal cutters.
Remove the nut and washer from the jack and put the bushing
through the hole from the inside. Now, you have a decision to
make. With the washer underneath the nut, there may not be room
for the nut to screw down past the end of the bushing, thus
interfering with the fit of the plug. Try putting the nut on
with the washer first; if there is any doubt, leave the washer
off. (Don't throw the washer out; save all hardware for future
There are many ways to hold the board in place. Screwing it
down is certainly possible; for doing so, you will need to get
spacers to hold the board away from the box slightly, so as not
to mash circuit connections against the box and, probably, bend
the board. You can also obtain doublesided foam tape from a
neighborhood hardware store, securing the board under the transformer and at the corners. I think it is sufficient to rely on a
block of styrofoam which is glued to the lid of the box.
By gluing a piece of styrofoam to the lid of the box, you
can solve two problems: If you position it right, this will keep
the battery standing up on edge. By doing a little creative
carving, you can accommodate the magnet of the speaker, and thus
hold down the board. The best source of styrofoam of different
shapes comes from packing material in all the little electronic
gadgets we buy. (I mean the funny-shaped block of styrofoam, not
the peanut-shaped, general-purpose packing material.) The best
thing to cement it down is Barge Leather Cement, gotten from
leather-goods stores or shoe repair shops.
Hints and Kinks
It is indeed a shame that 95% of my projects
have loudspeakers in them, since making sound holes for them and
mounting them is borrrrrring! Nonetheless, my methods are successful, and the projects look very nice.
The quickest way of getting sound holes is to punch a large
round hole with a "chassis punch," then cement plastic screen or
perforated metal stock behind this hole. However, a selection of
large-sized chassis punches will mortgage the farm, and the
resulting package is not nearly as attractive as a method I
learned from Gene Merritt, a fellow subscriber to the ol' Braille
You can use Vectorbord as a template for drilling nice
regular patterns of holes; the "A" pattern (available from Jameco
as 64AA18) is well-suited for this purpose. This pattern has
holes spaced at 0.265 inch intervals. You lay a piece on the
panel to be drilled, and drill through the holes with a No. 43
bit (this enlarges the holes in the Vectorbord, but does not ruin
it for use the next time).
Of course, the pattern I choose to drill depends on the size
and shape of the speaker; I decide on this by laying the Vectorbord on the speaker first, counting the speaker's dimensions in
"Vector holes" (with the aid of a braille stylus).
Most often, for round speakers, I decide on a diameter
first; then, when I drill the pattern, I leave out corner holes
as appropriate. I keep three No. 4-40 machine screws and nuts
handy; I drill a center hole and bolt the board down, then I
drill two edge holes and secure these. Then, I go after the
project until my wrist gives out and the neighbors complain.
The pattern I drilled for the continuity tester is basically
5 by 5, but with the corner holes omitted (thus having three
holes in the center of each side of the pattern). A square
pattern of 4 by 4 would be perfectly OK -- this represents 16
When I don't have any such Vectorbord (it does wear out,
eventually), I put Dymo Tape in a braille slate upside down (so
that the dots become dimples), whereupon I write a generous
supply of "K's." Laying down a few lines of K's works OK, too.
You then drill through the dimples; then throw away the tape.
No less tedious than drilling is cleaning up the holes
afterward. I use a 1/2-inch drill bit for this purpose, spinning
it in each hole to clear away the burs. If the box is a solid
color, you can do this on the front side as well. However, if
the box is painted, sighted folks don't like the results of
deburring the holes on the outside. Even though they feel raggedy, leave them alone in this case.
Very often, the speakers you get nowadays have no mounting
flanges. They are intended to fit cases which have been molded
for them (which is a real great favor to us). I have had good
results from gluing them to the panel if I use the right cement
and do a little preparation first.
The best thing I have found for gluing speakers is a Goodyear product called Pliobond Cement. (There are good equivalents; for example, Plibond by General Cement.) This cement is
rubbery stuff; if you slop a little over onto the speaker cone by
mistake, it doesn't "stop the show," as you might say (it is
meant to be pliable).
What generally fails in bonding the speaker is the cardboard
rim. More often than not, when you open a project whose speaker
is rattling around inside, portions of the cardboard are still
stuck fast to the panel. I have greatly improved the reliability
of my speaker-gluing jobs by sanding the cardboard rim down flush
with the metal rim. I lay a piece of coarse or medium-grade
sandpaper on a flat surface; then I rub the speaker vigorously,
face down, on the sandpaper until I hit the metal rim. After
this, the cement can bond to the cardboard and the metal, both.
It is also a good idea to sand around the pattern of holes on the
back side of the panel, thereby roughening the surface and improving the bond.
In gluing, I first clean the back of the panel and the rim
of the speaker with isopropyl alcohol. Then, I get the rim of
the speaker gooey with the cement. I never bother to apply glue
to the panel, even though they always say to wet both surfaces.
Make sure you know exactly where you want the speaker before
you set it down, and turn it so that the terminals face the way
you prefer. If you set it in the wrong place, you will have to
apply fresh glue before setting it down again. Once done, turn
the project over on its face, letting the speaker's weight keep
the pressure on, and split the scene for a day.
Applying Glues and Cements
I learned long ago that the
finger is the best applicator of glue (which is why I stay away
from "SuperGlue;" this can brutally stick yourself to yourself).
I have heard respected sighted people in the piano business
advocate using the finger; it is even more sensible for a blind
person. When you use your finger, you know just how much glue is
being applied, and you have a pretty good idea as to where it's
The trick is to keep appropriate solvents around to clean
yourself up. For white glue and animal glue, a handy bowl of
warm water is marvelous, along with a couple of heavy paper
napkins. For PlioBond and Barge Leather Cement, paint thinner is
OK. (PlioBond can be reconstituted with methyl-ethyl ketone.)
When working with epoxy, a bowl of isopropyl alcohol is appropriate. Keep everything ventilated when you use these organic
solvents, since they're rough on your endocrines.
You will be less annoyed with gooey fingers if you use a
non-dominant finger to apply glue. I usually use the middle or
ring finger of my left hand. Wrap any rings you have with masking tape (which is unnecessary when using white glue).
Before I glue anything, I always clean the surfaces with
isopropyl alcohol. The enemy of all glue bonds is oil, either
from your hands or from industrial processes in manufacturing.
Alcohol is a moderately good solvent for these oils, and it is
not fatal to breathe the fumes (within reason). In the process
of cleaning the surfaces, you will also clean your fingers, which
will prevent you from contaminating the glue as you apply it.
A person cannot say everything in a paper
like this (although there are readers among you who accuse me of
trying). There are things that a shop-worn person does that
"do-it-yourself" books couldn't cover, nor would the reader
remember them with screwdriver in hand. However, here are some
The project cabinets you buy are held together with self-tapping screws (unless they are of the Hammond brand from Canada,
these being of superior quality). The material in the box described here is pitiously soft, and the screws brutal; without
realizing it, you can tap new threads every time you insert a
screw. Therefore, it is essential that you learn to first turn
each screw backwards, feeling for it to "drop" into its threads.
Then, try turning the screw forward using the shank of the screwdriver, not the handle. If the screw resists even slightly, say
"excuse me," back up, and try again.
In drilling holes in precise locations, you usually cannot
get away with just placing the bit on the surface and pulling the
trigger -- the bit will wander before it begins to cut. In
metal, you first place a "center punch" in the desired location,
whereupon you bash it with a hammer two or three times. In soft
plastic like this, I keep a stray drill bit, perhaps No. 45,
handy; I place this in the desired spot and spin it between my
fingers, thus drilling a "center mark."
Also, in order for a drilled hole to "be where you put it,"
it is necessary to drill a pilot hole first -- a hole much smaller than the eventual size. Then, if it is critical, or if the
material is hard, drill several times with larger bits, doubling
the size of bit each time.
Keep scrap slabs of wood handy for drilling on, rather than
boring into your workbench when the bit goes through the work.
The slab of wood will also catch most of the "chip" (the shavings
you get when you drill); you can then just up-end the drilling
board into the wastebasket.
Deburring of drilled holes is always necessary, especially
on the back side. A bit much larger than the hole is very handy
for this. If you cannot reach the back side of the hole with a
drill bit, the burr can be cleared away with a small knife blade
that you don't particularly care about.
There are some nifty measuring tools for blind folks. AFB
(15 W. 16th St., NY, NY 10011) is reviving their "Rotomatic
Rule;" this is a calibrated screw, having sixteen turns per inch.
Almost exclusively, I use two measuring devices: the "Stanley
Combination Square" (also from AFB) and the "Rotomatic Rule."
I put the Stanley Square up against one side of the cabinet,
holding it with my ever-so-adjustable tummy, and bring the Rotomatic Rule to meet it from another side. Then, I place my center
punch or finger drill at their intersection, let the rulers fall
as I turn my attention to holding the centering device, and make
By now, it will have become obvious to you that "holding
clamps" and vises are a key to happiness. If you're stuck with
the kitchen table as a work space, at least get a small
"clamp-on-the-edge" vise from a hardware store, as well as some
sort of board clamp (see "Soldering, Part II," SKTF, Winter
Speaking of holding things, the hardest solder connections
to make are those in which the parts are poorly stabilized. For
example, soldering hookup wire is nearly impossible, if everything you do knocks it out of position. Get good at figuring
ways of stabilizing such wires. As mentioned earlier, you may
have room to clamp the insulated portion against an edge of the
board with an alligator clip. Wrapping the wire around the
board, or around an item on the component side, is something I do
most often. Wrapping the wire around the board clamp, or trapping it underneath, works too.
In principle, desoldering something is quite simple; you
merely reheat the items and pull them apart. Since the parts
you're working with will get hot, pulling on them with your
fingers can be uncomfortable -- and awkward. The best pulling
tool made is a set of "locking forceps" -- something you can get
from your doctor, or from tool suppliers (see "Soldering, Part
II"). An alligator clip sometimes works, as well as needle-nosed
pliers with a rubber band around the handles to squeeze them
When you pull a wire free of a solder lug (such as those on
the speaker and the jack), solder often clogs the hole, preventing you from inserting a wire next time. There are three ways to
handle this. One is to ignore it; wrap the lug around the outside next time and solder it that way. Another is to clear the
hole with a pointed instrument; an old dental pick is the best
thing for doing this. The third way is to heat the lug, then
slam or toss the part down on the table.
Suppose your project doesn't work, and the meager suggestions given here don't point the way toward fixing it. There are
three things you can do. You can ask a sighted pal to help you
trace through the steps again. You can quietly analyze which are
your weak points, get some junk parts and practice these operations on a scrap of board. Or, which is what I recommend, you
can gleefully take wire cutters to the thing, clean off the board
with isopropyl alcohol and an old toothbrush, buy new parts and
do it again.
Do you realize how little money this first attempt cost you?
First of all, the board and the box are still OK, and you didn't
have a chance to ruin the jack yet (you'll have a turn at this,
too; I've sent many to the great beyond). Therefore, you've had
hours of beginning lessons for under five bucks. (Your kid
sister could be dropping $10,000 a year on her Bachelor's
degree.) Truly, no matter how it's turned out, your initial
experience has been quite economical.
Any negative interpretation of your experience is artificial. Realistically, let us take stock of your individual accomplishments: you have installed four parts into holes that are so
small and close together that they can only be clearly felt with
your tongue (don't do much of that, by the way, since you'll get
tiny fiberglass slivers in your tongue). You've made ten solder
connections, and have tinned possibly four wires. Except for
chips and diodes, you are now intimately familiar with the most
common parts. I'd say, for five bucks, you got a pretty good
In your next trip to the store, buy two sets of parts. Any
you don't use here will not go to waste; variations on this
circuit abound in audible devices. So what if you have to start
over three times. When you're done, you will have a vital instrument. Your sighted counterpart, who builds a radio circuit
or a photo timer, only ends up with that toy, and not an instrument of daily use. Then, too, the person whose project worked
the first time has less experience at troubleshooting, and he is
behind you in the practice of manipulating parts.
First, now what you have one, you should read "Continuity
Tester Uses," SKTF, Fall 1983. Just for fun, build a couple of
the "attachments" for it that are mentioned there. Clip it
across the resistors in the "attenuator" of Part I in this series; the two resistors will give you very different pitches.
What's happening next time is a test amplifier, such as the
one described in "Point-to-Point Wiring on Perforated Board,"
SKTF, Fall 1980. If you want to get a head start, go ahead and
review that article.
The one to be presented will have three main circuit
changes: The regulated power supply will be omitted; a 9-volt
battery will take its place, this battery being bypassed by 250uF
(negative of the capacitor at ground). The output capacitor to
the speaker will be changed to 100uF, thus making the project a
little more roomy. Finally, a volume control will be included;
its bottom end is grounded, its arm goes through the 0.1uF input
capacitor to pin 3 of the LM386, and the top of the control will
accept the input signal (via another pesky jack).
By Bob Gunderson, W2JIO
The test oscillator described in this article is
one of the handiest gadgets for use in the ham shack or laboratory. It will oscillate from very low frequencies -- below 50
kilocycles to well over 100 megacycles. I use it as a calibrator
for my frequency counter, as a signal source for receiver alignment, as a means for checking crystal frequency and crystal
activity, and even as a marker generator.
If you plan to build this gadget, you'll surely want to
begin collecting surplus crystals; you can easily attach Dymo
Tape labels so that you will know each crystal frequency. My
collection includes a low frequency of 50 kc, and many 20 mc
units, plus a number of overtone frequencies. Since the test
oscillator is a Pierce circuit, these overtone crystals produce
their fundamental output which is some value around one-third the
marked frequency, though not an exact third.
The oscillator is fitted with an auditory gimmick circuit,
so that the operator can tell if the crystal is oscillating. A
2-pole 3-position switch makes it possible to disable the output
indicator when not in use. In addition, I have used a rechargable 9-volt Nicad battery and a built-in charger. An 18-volt
transformer feeds into a bridge rectifier with a limiting resistance to hold the charging current down to 10 mA. The transformer
is the type used with the Princess Telephones, and is outboard --
attached to the oscillator by means of an RCA type phono connector. It simply plugs into the AC line.
The oscillator is a simple Pierce Circuit, using an insulated-gate MOS Field-Effect transistor, type 3N139. However, any
good FET should work quite well.
I should mention that there are numerous crystal holder pin
configurations, so that it would be advisable to place various
types of crystal sockets on the panel. I have four, plus an
ordinary 5-pin socket on my unit and this pretty well accommodates most types. In addition, I made up a 5-pin plug with two
flexible leads connected to pins 2 and 4, with clips at their far
ends so that odd crystal units may be clipped into the circuit.
These parallel-connected sockets will provide some additional
capacitance, but it doesn't appear to have much effect.
The Pierce circuit is essentially a Colpitts oscillator in
which the feedback is a function of the input and output capacitance (from gate to ground, and from drain to ground, respective
ly) providing the necessary feedback. At the low frequencies,
additional drain-to-ground capacitance is needed, and I have
provided three toggle switches so that the necessary additional
capacitance can be placed in the system.
Caution -- When you use an oscillator of this type, you will
probably use some of the older crystals which are comparatively
large, meaning that their output amplitude is quite high. If the
positive-going swing exceeds the breakdown voltage rating of the
transistor (from gate to source), the FET will be destroyed. I
quickly learned this fact, and found it necessary to add a diode
clamp from the gate to the source and ground. Of course, there
is another option -- you may add a source biasing resistance,
properly bypassed, to limit the positive swing. I decided in
favor of the diode clamp because of my limited supply of 9 volts.
The source bias arrangement would, no doubt, work just as well.
My original unit -- the one built some years ago, and used
until the MOS transistor went West, used the original transistorized gimmick which I devised back around 1954. However, Earl
Quay, W4MKC, recently sent me a simple gimmick circuit which is
essentially an assymetrical multivibrator, and I have included it
in the rebuilt unit. This newer circuit is simple and works very
well -- more of this when we describe the circuitry. One day
when I attempted to show the unit to a group of radio amateurs, I
found that it didn't work, and upon checking, found that the FET
had burned out. The replacement lasted about 10 minutes, and it
was then that I decided to add the diode clamp. Measuring the
negative-and positive-going output voltages at the drain showed
that the positive signal reached something like 17.5 volts peak,
while the negative signal was only 5 volts. This occurred with
the larger quartz crystals. These measurements were taken, using
a small-signal germanium diode (a type 1N270) working into the
vacuum tube voltmeter. The two halves of the signal can be
measured by reversing the diode leads, and reversing the input
polarity of the VTVM. The addition of the diode clamp yields an
output signal which isn't symmetrical, but the positive excursion
is only something like 7 volts rather than 17.5; the negative
excursion is still the same.
As mentioned previously, the trick in making a satisfactory
wide-range oscillator is the use of sufficient feedback from the
amplifier's output to its input; this has been taken care of
through the use of 3 separate feedback capacitors in the output
circuit. These may be switched in separately, or they may be
placed in parallel to give the sum of the 3 capacitors. The
second essential part of the circuit is sufficient impedance in
the drain of the FET. For the higher frequencies, a 2.5 millihenry RF choke is used, and for the low-frequency end, a large 80
millihenry unit provided the necessary increase in drain impedance. These two chokes are connected in series, with the smaller
value directly at the drain. At low frequencies, this 2.5 mH
choke hardly exists, and the larger unit does the work.
The output of the RF oscillator is coupled in two directions
-- to a coaxial connector for application to the receiver, counter, etc., and also to the rectifier for forward-biasing the
auditory gimmick when the aural indicator is to be used. I have
thought that it might even be a good idea to couple the output to
a source follower, or an emitter follower, with a potentiometer
as its load, so that an attenuated signal could be available
(we'll leave that to the new and improved version built by another reader).
The layout of parts isn't at all critical. This unit is
built into a Keystone bakelite box measuring 2-1/2 inches high by
6-3/4 inches long and 5-1/2 inches front-to-back. These are
outside dimensions. It might be better to place the unit in a
metal container to provide better shielding. However, I use the
oscillator for direct pickup on the station receiver, so that the
unshielded construction is ideal. The panel is aluminum stock,
with the crystal sockets at the left end; the output coaxial
connector at the upper center, with the on-off-function switch at
the lower center. The 3 toggle switches for switching the capacitors into the feedback circuit are just to the right of the
crystal sockets. The connector for the power (charger) transformer and the speaker are at the right side of the panel. The
greater part of the electronics are mounted on a small piece of
perforated Vectorbord measuring about 6-1/4 inches long and 2
inches wide, mounted vertically along one edge of the panel, in
from the lower edge, far enough to allow the unit to fit inside
the plastic box. The circuit board is fastened to the metal
panel with small brass angle brackets. When the 3-position
switch is "off," the charger is connected to the 9-volt battery
for recharging the unit.
Pierce Oscillator Portion of the Circuit
sockets are connected in parallel, and one side of this arrangement goes to the gate of the oscillator transistor (3N139); the
gate also goes through the parallel combination of 33 pF (mica
capacitor) and 100K ohms, to the source, to the circuit ground
and to the minus 9-volt line. This gate also goes to the anode
of a 1N914 small-signal diode, with the diode cathode also
grounded. (This is the clamping diode used to limit the positive
output swing.) The source and substrate of the FET are connected
together and grounded.
The other side of the parallel-connected crystal sockets
goes through 0.01uF to the transistor drain, with the drain going
through the 2.5 mH RF choke, thence through the 80 mH RF choke to
the plus 9-volt line. This is a switched line which will ultimately connect to the 9-volt battery positive. The drain also
connects to a 100 pF mica capacitor, with the other side of this
capacitor going to the hot side of the output coaxial connector
(SO-239). Of course, the other side of the output is connected
to the panel common.
The drain connects to one end of three additional mica
capacitors (350, 500 and 1,000 pF); the other ends of these
capacitors each go to one end of their separate toggle switch.
The other ends of all three toggle switches are connected together and go to the circuit ground. With this arrangement, any one
of these capacitors, or all three, may be connected from the
transistor drain to ground.
This completes the oscillator, except for the coupling
arrangement used to rectify the oscillator's output, which biases
the auditory gimmick -- more of this later.
If you wish, the diode clamp may be omitted, and you can
apply source resistor bias to the circuit to provide the necessary protection for the insulated-gate FET. The only circuit
change consists of omitting the diode from gate to ground, and
connecting a resistance of perhaps 470 ohms, suitably bypassed by
a 0.01uF disc ceramic capacitor between the source and ground.
The remainder of the circuit is the same. I chose the diode
clamp because of the 9-volt limit.
You will find that some crystals are a bit sluggish, and may
not oscillate unless additional capacitance is switched into the
drain-to-ground circuit; the 3 switches will pretty well take
care of this problem. You may even add a pair of terminals for
adding even more capacitance if you wish. One of these would be
grounded, while the other would connect to the drain. You can
even use a capacitance decade at these terminals.
A small capacitance (100 pF mica) couples the oscillator to a shunt diode rectifier, and the output of
this diode provides the DC to forward-bias the auditory gimmick,
so that it produces an audio tone when the crystal is oscillating; no output will indicate that the oscillator isn't functioning. My original design used the earlier gimmick circuit, as
mentioned previously; however, the circuit provided by W4MKC
worked so well and required fewer parts, that I put it into this
Most of the readership is familiar with the simple transistor gimmick. Just to make sure, the circuit for it is described
Standard Gimmick Circuit
A PNP transistor is used in a
blocking oscillator, using a small audio output transformer. The
bias for this oscillator is provided by the output from an NPN
transistor. The input of the NPN transistor is fed from a DC
source -- from a meter movement, or in this case, from the output
of the shunt diode. If a silicon transistor is used as the DC
amplifier (the NPN transistor), forward bias should be applied to
its base via a voltage divider, inasmuch as this type of transistor requires something like 0.7 volts before conduction can
Any general-purpose PNP and NPN
transistors may be used. The emitter of the PNP oscillator
transistor goes to the center tap on the transformer primary,
with the bottom end going to the plus 9-volts. The other end of
the primary goes through a 0.01uF capacitor to the base. This
winding is tuned by a capacitor of about 0.01 to 0.05 uF. The
secondary of the transformer goes to the speaker. Minus 9 volts
is grounded. The base goes through a resistor (10K to 47K ohms
-- value not at all critical) to the collector of the NPN transistor. The emitter of the NPN unit, and the collector of the
PNP oscillator transistor, are grounded.
The input signal is applied to the base-emitter terminals of
the NPN transistor. If this circuit is used around transmitting
gear, the input leads should be suitably filtered by means of RF
chokes and appropriate bypassing. If forward bias is to be
applied to the DC amplifier, connect a high-resistance potentiometer across the 9-volt lines, and return the low side of the
meter to its arm, rather than to the circuit ground. Then,
adjust the potentiometer until the circuit just begins to oscillate.
The sensitivity of this circuit is quite dependent upon the
value of the base blocking capacitor -- the smaller the capacitance, the greater the sensitivity. Values from 0.1 to 0.01 uF
can be used, with 0.01uF providing a much greater change in pitch
for a given input signal. The audio output level does decrease,
however, with the smaller capacitance value.
This is really simple, and it takes less
room on the circuit board. I haven't really played with this
circuit, except as it applies to the test oscillator; however, it
does look promising. It uses a PNP and an NPN transistor, both
general-purpose types in an assymetrical multivibrator.
The emitter of the PNP transistor goes to plus 9
volts. Its collector goes directly to the base of the NPN transistor. The NPN's emitter goes through the speaker to minus 9
volts. The NPN unit's collector goes through 10 ohms to plus 9
volts, and this collector also goes through a 0.005uF capacitor
to the PNP transistor base. The PNP base also goes through a
470K resistor, thence to the anode of a 1N270 diode (1N34 will
do), with its cathode taken to a point X, which I shall explain
in a moment. The diode is shunted by a 1 megohm resistor. The
signal from the oscillator is injected through a coupling capacitor to the anode of this diode.
If the diode cathode and 1 megohm resistor junction is
returned to the circuit ground, this will forward-bias the PNP
transistor, and the multivibrator will "free-run." Returning
point X to plus 9 volts will hold the circuit in the idle mode
until the diode provides the necessary bias. The return point
for the resistor-diode junction at plus 9 volts may be by-passed
by means of a 0.01uF capacitor. The plus 9-volt lines for both
circuits are connected together and bypassed by a 1,000uF electrolytic capacitor.
The on-off switch is a 2-circuit, 3-position
unit. The arm of unit 1 goes to the plus of the 9-volt battery,
and the "off" position for this section goes to the charger
output. Positions 2 and 3 of this unit go to the plus 9-volt
line of the circuit.
The "off" position of the B side of this switch is left
blank. Position 2 of unit B is connected to the plus 9-volt
line; position 3 is connected to the junction of the diode
(1N270) anode, the 1 megohm shunting resistor, and the series
470K ohm resistor which goes to the PNP transistor base. The arm
of this second switching unit goes through a 100pF mica capacitor
to the drain of the crystal oscillator.
It was necessary to use this switching arrangement because
there was sufficient capacitance between the switch contacts to
excite the auditory indicator with the switch in its second
position; I wanted this position for just the crystal oscillator.
The multivibrator output is a square wave, and it finds its way
into other circuits, so that it is often a good idea to have just
the crystal oscillator without the indicator.
The Battery Charger
If you plan to use the ordinary 9-volt battery, you may skip this portion of the project. However,
the charger is very simple. I used a low-current 100 PIV full-wave bridge rectifier and the transformer used to operate the
pilot light in the Princess type telephone. If you have room in
the cabinet, you might wish to include the transformer. I ran
out of real estate, so I took this approach. The transformer
plugs directly into the wall outlet, and I fitted it with a
length of zip cord and an RCA phono connector, plugged into the
appropriate connector mounted on the panel. The connector is
hooked to the AC input leads on the bridge, with the minus output
lead connected to the circuit ground, and the plus connected
through a current-limiting resistance (620 ohms in my unit) to
the "charge" position (the "off" position) on the on-off switch.
The secondary voltage of this transformer is 15-18 volts, and the
charging current for the 9-volt Nicad is 10 mA, for a period of
14 to 16 hours.
My first unit used a standard 9-volt battery, but I often
left it turned on, and had a dead battery whenever I went to use
One final note about the sensitivity of this second auditory
indicator -- A small capacitor in the feedback circuit, from the
second collector to the first transistor base, provides higher
sensitivity than does a large one. I had originally tried a much
larger value and had just about given up the circuit. Of course,
the higher capacitance reduces the free-running frequency of the
circuit; the 0.005uF capacitor seems to be a good compromise in
Note -- The series capacitor connected between the drain and
one side of all the crystals is not absolutely necessary; however, if the two leads are accidentally short-circuited, or if you
have a short-circuited crystal, this places the 9 volts on the
gate and on the diode anode. The 0.01uF blocking capacitor will
have inductance above the resonant frequency, and this places a
limit on the operating frequency. I have found that putting a
2-inch loop of wire in place of the crystal provides an oscillator frequency of about 100 megacycles.
Note -- Another interesting observation I have made is that
some very low-frequency crystals appear to oscillate; however,
the oscillation frequency is not the one marked on the crystal.
Rather, it is usually a much higher frequency. For example, I
have some crystals marked "76 Kc," and find that they oscillate
at about 210 Kc. These low-frequency units are mounted to oscillate in their "sheer mode," or end-wise. Thus, the crystal plate
may be very thin. An X-cut 50 Kc unit would indeed be a very
large bar, if it were cut to oscillate at its "thickness" frequency. I also have a 16 Kc crystal, and when plugging it into
this oscillator, I find that it does oscillate -- not at its
marked frequency, but up around 100 Kc. No doubt, it is mounted
in such a way (between its plated electrodes) that it has a
thickness mode, however unintentional, allowing it to oscillate
at this odd frequency value.
For the most part, however, the oscillator provides output
at the specified crystal frequencies. If you use it along with a
counter, you will have no difficulty. I have not been able to
make this circuit operate at the very low frequencies, from 1
kilocycle up to 30. These sheer mode crystals are available for
use in various clock circuits.
Capacitors [Those used in the oscillator include: 33 pF, 350
pF, 500 pF, and 1,000 pF (all mica or polystyrene). An additional bypass capacitor (0.01uF disc or mica, etc. should be included
if source-resistor bias is used).]
- Two 100 pF disc ceramic or mica.
- If the original transistor indicator is used: 0.01 and a 0.05uF disc ceramic are included.
- Feedback capacitor in the multivibrator type indicator: 0.005uF disc.
- Power supply bypass: 0.01uF disc and a 1,000uF electrolytic, rated at 15 volts or better.
- 1N914 clamping diode and a 1N270 (or 1N34) bias rectifier.
- For the charger -- A bridge rectifier, 100 PIV at 100 mA
should do nicely. Even a simple half-wave rectifier should do
Resistors: (All resistors are 1/2 watt)
- For the oscillator: 100K ohms gate leak; 470 ohms if self-bias is employed.
- For the bias circuitry: 470K and 1 megohm.
- If the earlier indicator is used, any thing from 10K to 47K
ohms (value not at all critical). The smaller the resistance,
the greater the sensitivity. However, too low a resistance will
cause the oscillator base current to reach too high a value,
causing transistor burn-out.
- For the multivibrator indicator circuit: 10 ohms.
- For the battery charger, 620 ohms in the unit built here.
Its value should be chosen to limit the charging current for the
Nicad battery to 10 milliamperes with a run-down battery. The
capacity of these units is generally 100 MAH, and they should be
charged at one-tenth C or 10 mA.
- 3N139 Insulated-gate MOS transistor used for the oscillator;
any good FET should do nicely.
- General-purpose NPN and a PNP transistor used in either
indicator circuit (2N2222 is NPN, and 2N2907 is PNP).
- RF chokes: 2.5 millihenries and 80 millihenries.
- Switches: 3 single-pole single-throw toggle switches and one 2-pole
- Sockets for crystals, output connector, connector for charger, see text.
- Speaker: small 1-inch unit is used here.
- Transformer used in the original Gimmick circuit: Stancor
TA-20, any 500-ohm center-tapped primary to speaker voice
- Transformer for battery charger: The type used for illuminating the pilot light in the Princess telephone used here (18 volts).
- Miscellaneous hardware, perforated board, etc.
Basing Diagram for the 3N139 Metal-Oxide Field-Effect Transistor
Hold the transistor with the case facing down and leads up,
with the tab at the edge of the case toward you. Counting clockwise from this tab, the connections are: 1. drain; 2. source; 3.
insulated gate; and 4. substrate. These leads are arranged in a
I mounted them on the circuit board with small hollow terminals made especially for the purpose. These terminals fit into
the holes in the board; they are then peened over with a special
tool -- an automatic center punch, fitted with a suitable point
which fits an anvil, allowing the terminal to make a snug fit
with the top side of the board. The hollow terminal makes for
convenient wiring on the under side of the board, plus allowing
the transistor to be plugged into the holes and then soldered.
These terminals, along with the punch and anvil, are supplied by
Keystone Electronics, 49 Bleeker Street, New York, N.Y. 10012.
To go right along with the train whistle (SKTF,
Summer 1984), this is a toy siren. It emulates the new-style
electronic sirens; it has a button for ascending and descending
wail, as well as a "fast-warble" feature. Circuit afficionados
will appreciate the power FET on-off switch, as well as the fine
example of "zener-diode DC coupling." True to my tradition, it's
in the Summer issue, so you'll have it by Christmas.
This circuit uses a Signetics NE566V VCO chip (see SKTF,
Winter 1985) to generate a nice-sounding triangle wave for the
siren. An option is included to modulate this oscillator at a
slow rate, so as to simulate the "warble" that many of the modern
sirens can produce. The "warbler" is another NE566, producing a
3 Hz triangle wave. The main oscillator is fed into an LM386
The main pushbutton, which gives you the standard "wail,"
runs the VCO control pin (pin 5) by way of an RC circuit with
different time constants for charge and discharge. The charging
of a 5uF capacitor is taken care of by a 47K resistor which goes
from its negative end to the top of the pushbutton. Across this
capacitor is a voltage divider made up of 22K and 47K; this sets
the VCO voltage to the appropriate level, and its total resistance, 267K, governs the discharge rate (determines the descent of
This main pushbutton also "refreshes" the "on" switch.
Pushing it turns on a PNP transistor which, in turn, turns on the
gate of an N-channel MOS/FET, the channel of which is the power
switch of the device. A parallel RC circuit on the gate of this
FET (consisting of 1uF in parallel with 220K) keeps the circuit
alive in order to let the siren "run down" to sub-audible frequencies before shutting off the power.
The warbler is set up to free-run; it has its requisite
voltage divider on the VCO pin made out of fixed resistors and
everything (see sample circuits in SKTF, Winter 1985). As can
beseen from the literature, there is an oddball bias on the
output of the 566; this had to be accounted for when driving the
VCO pin of the siren -- which requires funny control levels of
its own. The warbler output and the siren's control pin are DC-coupled via a 6.8V zener diode, which just acts like a connecting
rod of the desired length. (This use of zener diodes for coupling was pointed out to me by an instructor in college; it's a
technique which can be forgotten if left to disuse. The catch is
that zener diodes are awfully noisy, and they should never be
used in low-level circuits.)
Whether or not the main switch is held down, the warbler
switch seems to keep the bias on the transistor high enough, on
the average, to keep the power switch alive in my unit. This may
vary from unit to unit, depending on the transistor gain and the
average value of the triangle wave being coupled by the zener.
If it does not work quite this way, the skilled operator will
soon learn to keep the main switch on when using the warbler
These oscillator chips really are meant to operate on volt
ages over 10V; control of them is unpredictable under this value.
For this reason, I chose the battery arrangement shown, which
consists of a 9V battery in series with an AA-type penlight cell.
Replacement of the AA cell need only be done for every second or
third 9V battery.
It should be noted here that this project could have been
designed around one of the commercial noise-maker chips that were
made for use in arcade games (pinball machines). The thing was
that these chips are as wide as the board onto which I fit my
circuit, and the arrangement for hooking them up is not trivial.
On the other hand, those chips are worth knowing about, and if I
ever get any spare time, I'll describe one. (Why don't one of
you ambitious builders write that article for us, yes?)
A 9-volt battery is connected in series with a
1.5-volt penlight cell to get 10.5V. The positive terminal of
the resultant battery goes to the VCC line. The negative terminal of the battery goes to the source of a power MOS/FET (Siliconix VN0300M or VN10KM, or any N-channel unit). The drain of this
FET goes to project ground. Between the gate and the source is
the parallel combination of 220K and 1uF (negative of the capacitor at the source). This gate also goes to the collector of a
PNP silicon transistor (2N2907). The emitter of this transistor
goes to the VCC line. Its base goes through 470K to one side of
the main pushbutton (SPST), with the other side of this pushbutton going to the negative side of the battery (not to ground).
On the NE566's, the following power (and other) connections
are made: (I put them both into a single 16-pin socket; this is
why I left out the power supply bypass on the warbler, which has
its pins 1 and 8 immediately adjacent to pins 4 and 5 of the
siren chip.) Pin 1 of both is grounded; pin 8 of both goes to
VCC. Between pins 1 and 8 of the siren chip is 0.1uF, located
close to the chip. As per instructions from the data sheet,
there is a 0.001uF disc capacitor between pins 5 and 6 of each
Pin 7 of this 566 goes through 0.1uF to
ground. Pin 6 goes through 4.7K to VCC. Pin 5, the control pin,
goes to the junction of a voltage divider; i.e., pin 5 goes
through 47K to VCC, as well as going through 220K to the negative
end of a 5uF capacitor. The positive end of this capacitor goes
to VCC. The negative end of this capacitor also goes through 47K
to the top of the pushbutton (the side of the switch that also
drives the transistor base).
Pin 6 of this 566 goes through 18K to
VCC. Pin 7 goes through 5uF to ground (negative at ground). Pin
5 goes through 470K to ground, as well as going through 47K to
VCC. The output, pin 4, goes to the anode of a 6.8V zener diode;
the cathode of this diode goes through 4.7K to VCC. This cathode
goes through another SPST pushbutton switch (warble switch) to
pin 5 of the siren.
Pins 2 and 4 of an LM386 are grounded.
Pin 7 is bypassed to ground by 5uF (negative at ground). Pin 6
goes through 10 ohms (1/2-watt) to VCC; pin 6 is bypassed to
ground by 100uF (negative at ground). Between pins 4 and 5 is a
0.1uF capacitor. Pin 5 goes to the positive end of a 47uF capacitor, the negative end of which goes through the speaker to
The output of the siren, pin 4 of the first 566, goes
through 220K, then through 470K to ground. The junction of these
two resistors goes through 0.1uF to pin 3 of the 386.
It was a tight squeeze, but I built this animal into a box
measuring 4.75 by 2.56 by 1.4 inches (Radio Shack 270-222). The
circuit board is just over 1.2 inches wide (thereby being twelve
holes in width), and it stands on edge along one side of the box.
If I had it to do over again, I believe I would try a larger
board lying flat on the bottom, and covering about 2/3 the
length. The way I did it just barely leaves room for a 2-inch
speaker on the bottom of the box. The pushbuttons are on the
opposite side from the board, and the batteries are mounted on
As far as board layout is concerned, the two NE566V's are
near one end, the large RC circuit and the on-off switch components extend slightly beyond the middle, and the amplifier is at
the other end. A single 16-pin socket accepts both 566's, and
this socket's long sides are parallel to the long edge of the
board. The 8-pin amplifier socket has its rows of pins perpendicular to the long edges of the board.
- 2--0.001uF disc ceramic
- 4--0.1uF ceramic or mylar
- 1--1uF 12V electrolytic
- 3--5uF 12V electrolytic
- 2--47uF 12V electrolytic
- 1--100uF 12V electrolytic
Resistors (1/4-watt 5%, unless otherwise
- 1--10 ohm, 1/2 watt
- 1--2N2907, or any small-signal PNP silicon
- 1--Siliconix VN0300M, VN10KM, or any N-channel "power" MOS/FET
- 1--National LM386 amplifier chip
- 2--Signetics NE566V VCO chips
- 1--8-pin IC socket
- 1--16-pin IC socket (or two more 8-pin
- 2--SPST pushbutton switches of your choice
- 1--2-inch speaker
- 1--AA battery holder (Radio Shack 270-401)
- 1--9-volt battery connector
- 1--Cabinet (Radio Shack 270-222)
- 1 or more--Kid, preferably not in your
[Actually, with purposefulness, the thing isn't very loud.
As designed, this is no instrument of terrorism.]
by Susan Fowle, NY6D
[Editor's note, August 2005: While much of this article is dated, it does show the format of a typical electronics catalog and how to give instructions to get around a standard electronics catalog.]
The goal of this article is to familiarize you
with the general contents of the Jameco parts catalog, their
ordering forms and procedures, so that you -- together with an
electronically naive reader -- can order parts. Or, if you order
by phone, you will know approximately what is available and how
to present your order.
Basic Rules and Procedures
The address and phone number are:
1355 Shoreway Road
Belmont, CA 94002
415-592-8097 (M-F, 7:00-5:00 PST)
Jameco's index is on the inside front page. There are two
order forms in the middle of the stapled catalog, and the information needed is: quantity, part number, data sheet, price each,
and amount extended (price each times quantity). Attached to one
of the order forms is an addressed envelope without postage.
More order forms and envelopes are sent with your order. IMPORTANT: Jameco now requires an order of $20 minimum. Prior to
July 1985, the minimum was $10 [GRRRR!].
Jameco offers data sheets for 30 cents each on "most items."
This is mainly for IC's, and formerly included all the information found in data books, such as pinouts, typical applications,
graphs of various operating parameters, and truth tables. Now,
however, the data sheets contain only basic recommended operating
conditions and electrical characteristics. Jameco appears to be
photocopying only the first two pages of the data book information for each IC. They do say more information may be requested
at an additional cost. The 30-cent data sheet I received on one
IC did not even include the pinout of the chip, so I recommend
requesting all available information if you must obtain chip data
Jameco requests $1 for postage and handling to obtain their
free catalog, but they will send future catalogs and sales flyers
free to active customers. If you order from Jameco, they assign
you a customer number, which is found on your invoice, as well as
on the upper right side of the address label on the catalog's
back cover; they request this number on the order form.
In 1985, for domestic (USA) orders, postage and handling is
5% of the total order ($1 minimum). Insurance, if you want it,
is $1.50, and Jameco is not responsible for uninsured parcels.
Tax is 6-1/2%, and is applicable for California residents only.
Jameco will accept checks, Mastercard or Visa. There is a $10
fee for returned checks. COD is available, but you cannot pay
COD with a personal check.
All claims for defective material must be made within 60
days; include the defective material for testing purposes, Jameco's invoice number, and the date of purchase.
If parts are returned to Jameco due to customer error, you
must pay all extra fees plus a 15% restock charge.
Claims for shortages or damages must be made within 10 days
after receipt of parcel. If a part is on backorder they will
tell you; this information is probably on the invoice, so check
it first if you receive only part of your order. In my experience, Jameco usually has parts in stock.
Jameco sends sales flyers at least twice a year. These
flyers are numbered; if you order from a flyer, be sure to include the flyer number on your order form. The flyers contain
new prices for old items, items not listed in the regular catalog, "special sale" prices, and some items which are listed at
their usual prices.
What's In It?
At last we can get to the fun stuff, and contemplate the
contents of the catalog.
As much as possible, Jameco uses the "generic" part number
for IC's. IC information includes part number, number of pins
(helpful in determining socket size and, perhaps, whether you are
ordering the proper chip), function and price. IC's are listed
by the following types:
7400 Series (TTL):
Part numbers are preceded by SN (a Texas Instruments tradition), and followed by N (signifying plastic packaging). Ex.,
The following types of 7400 IC's have no prefix or suffix:
- 74F00 series (Fast)
- 74H00 series (High Speed)
- 74L00 series (Low Power)
- 74S00 series (Schottky)
- 74LS00 series (Low-Power Schottky)
- 74ALS00 series (Advanced Low-Power Schottky)
Intersil IC's are listed by Intersil numbers.
4000 series IC's are prefixed with CD (an RCA tradition).
74C00 (CMOS) and 74HC00 (High-Speed CMOS) have no prefix
The linear IC's have a more complicated order and part
number. These IC's are listed in numerical order, regardless of
the alphabetical prefix (ex., LM317T precedes LF353N). The pins
column lists the "type of package" (if it is not DIP). It would
be difficult to be sure of the suffixes used for the linear IC's
(and some of the IC's listed later), but the following may give
you a clue.
In general, the suffix N is used for most, but not all, of
the DIP (Dual-Inline Package) IC's.
The suffix K denotes TO-3 package (diamond-shaped metal
package with round capsule on top, and two pins underneath -- the
flanges of the case being a third connection).
Suffix T denotes TO-220 (rectangular metal back with square
IC package mounted on one side, and having three pins on one
Exar linear (ex., XR2242) and RCA linear (ex., CA3130E) are
Also separately listed are Signetics IC's, DTL (Diode-Transistor Logic), HTL (High-Threshold Logic), the National 8000
series, and Fairchild 9000 series. The Digitalker chips are also
There is, for different manufacturers' numbers, a cross
reference guide for RAM's, PROM's and EPROM's, as well as listings for Memory subdivisions: Static RAM's, Dynamic RAM's,
EPROM's, PROM's, ROM's.
There are subdivisions of Microprocessors and associated
components (subdivisions: 5000, 50000 series, Miscellaneous
circuits, A/D and D/A converters, CRT controller chips, Disk
drive controller chips, UART's, Generators, Telephone/keyboard
Microprocessor components are subdivided, but basically
pertain to Z80, Z8000 series, 6500 series, 6800, 68000 series,
8000, 80000 series).
(Hope you wanted to know about IC's. That was a lot to
describe, as well as to skip over.)
IC sockets are available in several types:
- Zero-Insertion Force sockets and
- IC Soldertail - Low Profile (Tin) (part
numbers are 8 pin LP, up to 40 pin LP).
- Soldertail Standard (Gold) (part
numbers: 8 pin SG to 40 pin SG).
- Wire-Wrap Sockets (Gold) Level 3 (part
numbers: 8 pin WW to 40 pin WW)
- Header plugs and covers and TO-3 sockets
Information on precut crystals is given for computers, TV
colorburst, etc. -- from 1 MHz to 49.89 MHz. This includes what
they are used with, case size, and load capacitance (for parallel
For diodes and transistors, generic numbers are used as
their part numbers. Important specifications for these semiconductors are also listed.
1/4 watt, 5% carbon film resistors are the only fixed resistors available in specifiable values. Values range from 2.2 ohms
to 10 megohms. Resistors must be ordered in quantities of 5 each
per value. All values are mixed in one package (unless individual packaging is requested, which, for less than 100 pieces, costs
an additional 5 cents per value). Above 100 pieces per value,
cost includes individual packaging for each value. There are
discounts for quantities beyond 500 pieces.
Potentiometers include the popular square top-adjustment,
single-turn type, and the long rectangular 15-turn type. For
either type, specify standard resistance values of 50, 100, 500,
1K, 2K, 5K, 10K, 20K, 50K, 100K, 200K, 500K or 1M. Part numbers
are 63P-(value) for single-turn pots, and 43P-(value) for 15-turn
Several types of capacitors are offered: Miniature aluminum
electrolytics are listed in "axial" (leads at both ends), and
"radial" (both leads on one end) versions. Other specifications
for each value include WVDC, surge VDC, approximate dimensions in
inches, and then the part numbers. For a 100 uF 25 WVDC axiallead electrolytic, the part number is A100/25. For the same
value in the radial-lead type, the part number is R100/25.
Values available are: A.47/50 to A2200/16, and R.47/50 to
R1000/16. Some values may be obtained in more than one WVDC.
Other types of capacitors are listed as follows: dipped
tantalum (values in uF, are specified with part numbers of TM
0.1/35 to TM 100/6). Disc capacitors have part numbers such as:
(pF values) from DC 10/50 to DC 470/50, and (uF values) from DC
0.001/50 to DC 0.1/50. Mylar capacitors have numbers of: (uF
values) from MY 0.001/100 to MY 0.47/100. Silver-dipped mica
capacitors have part numbers which are more involved: (values
from 10 pF to 1000 pF). Part numbers are DM15-100J for 10 pF,
DM15-101J for 100 pF, and DM15-102J for 1000 pF.
For trimmer capacitors: TC 2-8 is part number for value of
2-8 pF; other part numbers and values are TC 3-12, TC 3-23, TC
4-34, and TC 6-70.
Assortments of each type of capacitor are offered at substantial savings. Values included are marked with * to the left
of the part numbers.
Various types of switches and relays are offered.
Audible devices include a few small speakers, a buzzer, and
the SC628 Sonalert.
Tools include soldering irons, solder, and crimping and
Grab-bag specials are assortments of good parts, usually
costing less per piece than you will find otherwise; generally,
values are not specifiable, and you will have to sort items such
as resistors yourself. The items may be different in each catalog, so a reader will be necessary here.
The page of transformers, fuses and battery accessories
includes DC wall transformers (adapters) from 6 VDC to 10.5 VDC.
If you buy these, be sure to check plug polarity and operational
viablity of each unit. (I have gotten units that were shorted,
open, vibrated and got hot, as well as with center conductors
negative in one shipment and positive in the next.) Be careful!!
Computer cable assemblies are available in various forms,
and you can even order custom-made lengths with specified connectors.
The pages of "OK Products" include tools for wire wrapping,
DIP/IC insertion and extraction, desoldering and drilling.
Vectorbord comes in 3-hole patterns: the A pattern has hole
centers spaced 0.265 inches apart, with 0.093 inch diameter
holes; H has 0.10 inch spacing with 0.062 inch holes; P has 0.10
inch spacing with 0.042 inch holes.
Three materials are available: phenolic with hole patterns
A or P; epoxy-glass with patterns H or P; glass-epoxy with one
side copper-clad, having hole pattern P. Phenolic hole pattern A
is 3/32 inches thick; all others are 1/16 inches thick.
Vectorbord comes in various lengths and widths. In the 1985
catalog, the part numbers are labeled "Stock No." Vector terminals for soldering and for wire wrapping are available, as are
insertion tools. Be sure the terminals match the hole size of
your Vectorbord, and that the insertion tools match the terminals. Various types of Vector etched circuit boards for general
use (and for specific computers such as Apple plugboards) are
Global Specialties products include about four styles of
solderless breadboards and protoboards, accessories for same, IC
proto [test] clips, test equipment, instrument cases and hardware.
Also listed are regulated power supplies, keyboards, kits,
disk drives, diskettes, computers, peripherals and accessories.
Many items are available which have not been mentioned in
this article (oh my gosh, you mean there's more?). The indexes
of the Jameco catalog, and probably other often-used electronics
parts catalogs, may be made available in some accessible format
at a future date (clip that hedge!).
Well now, a new kind of thing has appeared -- as of this
issue -- embodied in Ms. Susan Fowle's article, "The In's and
Out's of the Jameco Catalog." This kind of thing can hand us (on
a zinc platter) a new measure of independence. Our thanks to
you, Ms. Fowle, for giving us this fine distillation of material;
it makes me want to pick up the phone and buy stuff. (Could it
be that the motivation for doing this mammoth job comes from your
husband yammering all day, "Could you please read that?" "No,
read that." "Heah! Read that!"?)
The "In's and Out's of Jameco" is a landmark beginning; the
choice of company was perfect, since it is the most useful organization I know of to the individual experimenter. Yet this idea
would die right here and now without sighted assistance in doing
the next one. Until -- indeed, if ever --" data bases" get good
enough so that a blind person, with his computer, can browse
through the world of parts, this kind of "distillation" cannot be
affected by your lights-out editor. (I have tried minor attempts
at this kind of thing -- notably the article on solderless breadboards in 1981; the error rate is unacceptable, and communication
with beset readers was stressful for all concerned.)
Although good-ol' Susan has made tenuous overtures in the
direction of doing another such piece on another supplier, why
leave this job all up to one person? Half of you guys are around
sighted classmates or hams who could try their hand at authorship
in a similar vein. Get the smartest guy you know by the lapels
and bark, "Say, how would you like to become a published author?"
So what if it takes a couple of tries; send the paper to me, I'll
critique it and send it back for revision, and we may end up with
material that gives us key phrases for the "phone call to the
supplier." (Please don't put someone to hard work, only to find
out that the outfit doesn't do mail-order business.)
In the meantime, I inherited an idea from my dad which may
be of use. Every few years, he would hire a neighborhood kid to
read the index of the Allied Radio Catalog onto a tape, just so
he could get an idea about what was out there to be had. He
would write out a list of things he wanted to know more about,
and pursue these items in more detail. This sort of thing, I
could do for us. As examples, tell me that more of this wouldn't
The following is taken from the catalog index of TechniTool, and covers only the letter "E":
E.C.2000; ETM Pliers; Economy Tool Boxes, Edge Protectors,
board; Edsyn Products, Eklind Hex-Key Sets; Electric Edger;
Electrician's Kit; Electrician's Knife, Electrician's Scissors;
Electro-Mechanical Kit (I don' know what it is, but I want that);
Electroplating Tape; Electronic Assembler's Kit; Electronic
Designer's Kit; Electronic Handy Pack; Electronic Timer; Electronic Operator's Kit; Electronic Specialty Kit; Electronic
System-Maintenence Kit; Electronic Pliers (ouch); Elements,
Torch; Emergency Kit; Endeco Desoldering Irons; Engineer's Tool
Kit; Engraver, Electric; Engraving Cutters; Epoxy Dispensers;
Epoxy; Esico Solder Pots; EtchoMatic Etcher; Eveready Flashlights; Extension Cords; Extra-Deep Cases; Extractor, DIP; Extractor, Lamp; Extractor, Lead and Shield (I assume that this is
a stripper for coaxial cable); Extractor, Screw; Eyelets.
Although the Edmund Scientific catalog has no index, it does
have major headings that jump out at you like:
"Complete kit turns any 12-to-19 inch TV into a giant TV
projection system." "It's a watch; it's a radio; it's an alarm."
"A thinking light switch." "It's the best news in home heating
yet." "SuperBug picks up voices on the telephone -- and right
through concrete." "Now your incandescent lightbulbs will burn
for ten years or longer." "Drive pests away safely with our
Sonic Sentry." "The Fischer 'Gemini II' Metal Detector is made
for professionals." "Construct Geodesic Dome buildings easily
with 'Star Plates'."
Now, the next question is, should I reprint this stuff in
the valuable pages of this magazine, or should I just issue tapes
with the "smart kid" reading this material at break-neck speed?
You decide, please. Send a card with your preference (and any
other thoughts) to me, before I go ahead and do the wrong thing.
So far, I have permission to reprint from the following
Cole-Parmer Instrument Company; Digi-Key Corporation; Edmund
Scientific Company; Jensen Tools, Inc.; Kulka Smith, Inc.; Small
Parts, Inc.; Techni-Tool, Inc.; and Vector
In my usual tradition, have a good summer. (I couldn't say
have a good fall -- that would be rude.)