A Quarterly Publication in Braille Talking Book and IBM Diskette Editions from The Rehabilitation Engineering Center The Smith-Kettlewell Eye Research Institute

Bill Gerrey, Editor

The Smith-Kettlewell Technical File

A Quarterly Publication of
The Smith-Kettlewell Eye Research Institute’s
Rehabilitation Engineering Research Center

William Gerrey, Editor

Issue: [current-page:title]

Original support provided by:
The Smith-Kettlewell Eye Research Institute
and the National Institute on Disability and Rehabilitation Research

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During a visit to the Braille and low-vision resource room at Lawton Alternative Elementary School in San Francisco, this author met two 5th-grade students who were impressive in intellect and who had gotten some exposure to computers. Talking to Mr. Jerry Kuns, it was further evident that those students had performed very well at a "computer camp" sponsored by Mr. Kuns's project, "C-TEC."

It occurred to this author that giving a little volunteer time to these young chaps would be fun, and that seeing a professionally employed role model would be good for them. Furthermore, if any teaching materials were born of this activity, they might be worth documenting for others to build on.

In conversation with Ms. Jill Patton, the senior staff member of the blind and visually impaired students' program at Lawton School, an arrangement was made to hold weekly sessions of simple laboratory work in the resource room.

A key aspect of the program's success was recommended and orchestrated by Ms. Patton, who suggested that the "classes" should include sighted friends of the blind students. It turned out that this broadened view of the program was vital; the inclusion of the blind student's friends led to experimenting with the tools and materials between sessions, which is eminently desirable. Also, as it turned out, this integrated arrangement was necessary to increase attendance.

Six sessions were held -- one of these was devoted to free-wheeling exchange, and for experimenting with a donated set of military field phones. For the five other sessions, formal class lessons were prepared; supplemental written notes were drafted and are presented here.

For the most part, no iron-clad connection was maintained between the laboratory experiments and the written lessons -- the papers were intended as supplements. (The exception to this was the construction of the "Say When," which was built as written.) It was the author's intention that the written supplements of this course stand by themselves as useful material for young beginners. Suitable exercises for laboratory sessions are described in this Instructor's Manual.

A fair question to ask is, on what "level" is this material written? Except for technical terms, the wording is simple (although it is undeniable that the author is not a professional educator). It is my feeling that the student's fascination with electronic products would be most important, and the exposure to simple tools and mechanical processes would have to have been encouraged. Most assuredly, these notes call upon the reader's ability to make associations with real materials. I suspect that a suitable experience base would include changing radio batteries, dealing with the plugs and sockets of modern appliances, and investigating the bins in hardware stores.

It is the author's hope that wholesale modification of this course will be undertaken by its users. Besides tailoring it to suit individual needs of students, refinement of the "Kid-Start Course" by educators is exactly what the author hopes for. I only ask that general statements of progress and evaluation be sent to Smith-Kettlewell Eye Research Institute, where a record can be kept to assess the value of such programs and text materials. (Please address these comments to me, Bill Gerrey, Smith-Kettlewell Eye Research Institute, 2232 Webster Street, San Francisco, California 94115.)

[Author's Update: Three of the blind fellows are now in their last years of high school. They give this course credit for kindling their technical interests. One has his ham-radio license, one is a confirmed computer hacker, and the third has diverse interests -- computers and model trains.]

Tools and Materials

The items required are minimal. They might be procured by donation. Excluding the Audicator (an optional $115 item), the cost of the items below would be less than $100. Not every item is needed in duplicate for each student; the tools and whole projects can be shared.


1. A Phillips screwdriver with a No. 1 bit.

2. A flat-blade screwdriver with a 3/16-inch bit.

3. A small gimlet (sometimes called a "screw starter," it is a small tapered drill with a T-shaped or wire-loop handle).

4. Diagonal wire cutters.

5. Adjustable wire strippers.

6. Scraps of sandpaper -- Medium or coarse (grit designation of 100 or lower) -- for stripping enamel off the ends of "magnet wire."

7. Some sort of test amplifier capable of making low-level signals audible (such as those from a microphone). This could be a donated small tape recorder with a monitor earphone. An ideal device is the Radio Shack speaker-amplifier, No. 277-1008 for $12.

An optional luxury is to have an "Audicator" by Science Products, 1043 Lancaster Ave., Berwyn, PA 19312. An audible continuity tester, this is ideal for demonstrating switches, testing earphones and speakers, etc. The Audicator's price is $115 ($92.50 for the Audicator itself, and $22.50 for the "test-lead" attachment). A second-best substitute for this, however, is to outfit the "Say When" -- described in the lesson notes -- with alligator clips (in place of the sensor). The Say When circuit will give an audible indication when it is presented with a continuous electrical path. The Audicator has the advantage of indicating -- by the pitch of its output -- the conductivity of the electrical path.

Electrical Supplies and Components

1. Magnet wire, such as Belden Wire Co. "Beldsol No. 8053" or any 26-gauge enameled wire. About 200 turns of this is wound onto an emptied spool of the hookup wire listed below. (Any motor rewinding shop can supply this wire, or you can contact Belden Wire Company for a local dealer.) Belden Wire and Cable Co., PO Box 1980, Richmond, Indiana 47375: Phone: (800) 235-3361.)

2. Three-spool package of hookup wire, Radio Shack No. 287-1304.

3. Small-gauge 2-conductor cable -- often called "speaker cable" (Radio Shack 278-1301, DigiKey No. W200-100-ND.

4. Alligator-clip audio patch cord, Radio Shack No. 42-2421.

5. Fourteen-inch alligator leads, Radio Shack No. 278-1156.

6. Battery holder for two C-cells, Radio Shack No. 270-385.

7. Battery holder for four D-cells, Radio Shack No. 270-396.

8. "Knife switch," Radio Shack 275-1537. (This is an optional component; its purpose is to show how a switch actually works. The author suspects its availability is temporary, so it is not really used in the experiments. Edmond Scientific has a complete selection of switch configurations in their knife switch collection; SPST, SPDT, DPST, and DPDT units are Cat. No. 38,805, 38,806, 38,807, and 38,808, respectively.)

9. One SPST ("single circuit") light switch, a standard hardware item.

10. One SPDT ("three-way") light switch, a standard hardware item.

11. One doorbell button (with a notch filed in the rim for hookup wires to pass through), a standard hardware item.

12. One simple doorbell or door buzzer, a standard hardware item.

13. One Radio Shack chime module, No. 273-071. (Note: this chime has become rather expensive -- about $12. A viable alternative is the piezo-electric "beeper" of item 14 below, which can also be used in telegraph sets and other bell/buzzer applications.)

14. The ubiquitous Mallory Sonalert found in everything from airport metal detectors to microwave ovens. It is high-pitched and unpleasant sounding, but it works well in these projects (although attention must be paid to the polarity of its hookup). This is Radio Shack No. 273-060, and a Panasonic version is sold by Digi-Key, No. P09928-ND.)

15. Small alnico magnets, such as Edmond Scientific assortment No. 42,188.

16. Small motors, such as Edmond Scientific assortment No. 1304 or 35,128.

17. Assorted woodscrews or suitable self-tapping screws (round-head or pan-head); 3/8-inch No. 4's, 1/2-inch No. 4's, and 1-1/2-inch No. 6's.

18. Pieces of soft wood suitable for mounting the above items and "breadboarding" circuits -- perhaps 8 by 12 inches.

19. Assorted C-cells and D-cells, some weak and some good. (Two good C-cells and four good D-cells are needed.)

20. A discarded alkaline 9-volt battery.

21. A sensor for the Say When. (This item was home-made; details sufficient for duplicating it are given in Lesson II of this manual.)

Lesson Plans

The structures of workable activities are outlined here. The author would like to encourage changes, based on having access to more interesting equipment, or based on better ideas.

Depending on the students -- how good they are with their hands -- and the availability of duplicate materials, sharing the work among students will be done differently for each situation. However, with only one setup, the author's experience was that jobs could be traded off; the friendships in my group were such that banter and playful criticism kept the session lively, but in focus.

Note that each lesson is accompanied by an equipment list. Such items as tools and the breadboard (with its woodscrews) are not listed each time. Common sense will prevail.

Lesson I

Cells and Batteries


1. Small DC motor.

2. Battery holders for C- and D-cells.

3. Alligator clip leads.

4. Assortment of cells; include some weak ones and some dead ones.

5. One dead 9-volt alkaline battery.

6. One SPST light switch.


1. Touch the motor's wires to the terminals of a good cell. Demonstrate that reversing the wires reverses the direction of the motor.

2. Demonstrate the fact that, if you connect the motor to a weak cell, it runs slower (and makes a sound of lower pitch). Point out that if you remember about how fast the motor should run on a good cell, a motor can be used as an audible battery tester.

3. Demonstrate the fact that the motor runs the same speed regardless of the size of cell -- C or D. No matter what size it is, 1-1/2 volts appears at its terminals.

4. Without a holder (using kids to hold them together), connect the motor to a series of two cells, three cells, and (briefly) to four cells; the fact that the motor runs faster with each added cell makes a crude audible voltmeter. (Alligator clip leads will be necessary to extend the motor leads.)

5. Place four D-cells into the holder. Connect one end of the motor to the negative terminal of the holder; then trace through the series set with the motor's free lead, showing that the cells are electrically connected as if they were all in line. Take them out of the holder and show the jumpers that connect them in series.

6. With a screwdriver and/or the diagonal wire cutters, uncrimp the bottom end of the 9-volt battery and show that it is made of six tiny cells.

7. Caution! Under no circumstances should you open the individual cells for examination. The electrolyte in alkaline cells is caustic, and must be avoided.

8. Preliminary to lesson III, use the breadboard to connect the motor, in series with the SPST switch, to the 2-cell battery holder.

9. Fashion a paper fan to the motor shaft.

Lesson II

The "Say When"

Note: A "sensor probe" was prefabricated by the author and brought to the session.

The insulator block is a small slip of plastic -- either cut from the lid of a plastic box or taken from stock found in architectural supply dealers (large hobby shops). The piece shown measured about 7/8 inches wide and 2 inches long. A half inch in from the top end, and 3/16 of an inch from each edge, small holes were drilled to accept the wire teeth (a No. 50 drill was used). Likewise, 1/2 inch from the bottom and 3/16 inch from each edge, "clearance holes" were drilled to accept No. 4-40 1/2-inch long machine screws (a number 40 bit was used).

The wire used for the teeth was cut from large unpainted paper clips (2- by 3/8-inch). First, the two wires were inserted in the small holes so as to protrude 1-1/2 inches out the front; then, sharp right-angle bends were put in them so they would run down the back of the plastic board to the screw holes. Next, the screws were inserted from the front side, whereupon the wires were looped around them on the back and secured with nuts. Extra nuts were put on so that wires could be attached.

Finally, the protruding ends were first bent up, then over, so they would hook over the edge of even a thick cup, reaching down less than an inch into the vessel.


1. An 18-inch cable for the sensor. This could be a twisted pair made from hookup wire of any color, or a length of 2-conductor speaker cable.

2. Battery holder for four D-cells.

3. Radio Shack chime, No. 273-071. Alternatively, a Malory Sonalert, Radio Shack No. 273-060, Digi Key No. P9928-ND.

4. Home-made sensor assembly (see above).


(If the 273-071 chime is too expensive, or if it becomes unavailable over time, the Mallory Sonalert, Radio Shack 273-060, will be described as well.)

1. With the chime's positive lead and control lead twisted together, demonstrate it on one cell, two cells, then the prescribed four cells. The black wire goes to battery negative, while the red and white wires go to battery positive. (Be advised that this chime module has gone through at least one design change so far; the author suspects that the color of the control lead might not always be white -- from unit to unit.) Note that it may not work on two cells, and it certainly won't on only one.

2. [For the blind technician: An "active" light probe can easily identify the black from the other two leads. From this point on, the red and white can be identified by performance of the chime. As both red and white (the latter being the "control" lead) go to the positive of the battery, disconnecting one of these can indicate which one is which. Lifting the white control lead from the battery will allow the chime to finish its "ding dong" sequence, while disconnecting the red supply lead will interrupt the sound of the chime immediately. Depending on the vintage of your chime module, pure trial-and-error testing (not knowing which is the black negative lead) may be risky; while my newest device has survived all combinations at 9 volts, I have cooked earlier units. Very early versions were to operate on 3 volts; I burned out one of those by applying 9 volts, so read the package.]

3. Demonstrate when connecting wires by screws. The wire should be wrapped around clockwise, so as the screw is tightened, the wire will tend to wrap, not unwrap.

4. Mount the 4-cell holder and the chime on the breadboard using No. 4 screws.

5. Fashion a cable for the sensor -- either a twisted pair of hookup wire, or 2-conductor speaker cable. Make this perhaps 18 inches long.

6. Illustrate use of the stripping tool; strip the ends of this cable.

7. Using extra nuts on the bolts of the sensor, attach one end of the cable to it.

8. Twist together the red battery lead, the red supply lead of the chime, and one free wire of the sensor cable; fix these under a no. 4 woodscrew.

9. In like manner, attach the chime's control lead (white) to the other sensor wire and hold these under a screw head.

10. Finally, with another woodscrew, connect the negative lead of the battery to the negative lead of the chime (both black in color).

11. Test the "Say When" as per the procedures in the students' notes.

12. Where possible, the "Say When" can be tested with other liquids; for example, distilled water or oil will not cause it to sing.

13. Note: There are enough tasks here to parcel out to various participants. One can make the cable, another can be mounting the chime, a third mounting the battery holder and testing for good cells (using a motor as the tester), and so on.

Equivalent Say-When Circuit:

The above chime is expensive, and it is a specialty item. A very common audible indicator is the Malory "Sonalert"; a Radio Shack part number is 273-060.

The Sonalert is a 2-lead device. The black lead goes to the negative of the battery. The red lead of the Sonalert goes to one wire of the sensor, while the other sensor wire goes to the positive of the battery.

This is not a very interesting circuit, but it will always be available. The sound of the Sonalert is not interesting either; it emits a 2.4kHz tone when there is electrical continuity at the sensor.

Lesson III



Note: A little preparatory work must be done on the pushbutton doorbell switch. As purchased, its bell-shaped housing provides no means for hookup wires to emerge from its underside (normally, it completely covers a hole in the door jam from which doorbell wires emerge). So that it can be used on a breadboard with wires coming out from under it, a notch should be filed in the rim of its housing to provide an escape route for these wires.

1. Hookup wire.

2. Alligator clip leads.

3. "Say When."

4. SPST, SPDT, and pushbutton switches.

5. Junk-box knife switch (or Radio Shack No. 275-1537, while still available). (This is strictly to illustrate what's inside a switch.)

6. Any bells, buzzers, motors, etc.

7. Other varieties of switches: magnetic reed switches, mercury "tilt" sensors, a telegraph key, a multi-position rotary switch, etc.


1. Outfit the "Say When" with alligator clips; this can be done by cutting clips off one end of two 14-inch clip leads and screwing their stripped ends down in place of the sensor.

2. Touch the clips together to show that the sounder will detect when they are electrically connected.

3. First loosen the screw terminals on the various switch units to connect the alligator clips, then test the various switches to see what they can do. Show the SPST ones first; then show that you can make the SPDT unit "turn something on" in either position.

4. [The so-called "3-way" (SPDT) wall switch may come in a variety of terminal configurations. On ours, the "swinger" is a screw near one end, with positions "1" and "2" being located across from one another near a "ground" terminal at the other end of the switch body.]

5. Make a circuit which illustrates use of the SPDT switch. For example, as per the descriptions in the students' notes, make it switch between a bell and a motor.

6. Build a 2-speed motor (perhaps with a paper fan attached to the shaft). This is done using the SPDT wall switch to select a tap on the 2-cell battery holder as follows:

7. Mount the holder for two C cells on the board using number 4 woodscrews. If desired, mount the 3-way switch to the board using 1-1/2-inch woodscrews (although depending on the type, of switch, mounting it may make connections difficult). You may wish to tape the motor in place as well.

8. With a short screw, connect the negative battery lead to one of the motor leads. Connect the other motor lead to the swinger terminal of the switch (which may entail joining the relatively short motor lead with an added length of hookup wire -- which is done with another screw on the board).

9. One position of the switch goes to the positive of the battery. Install the two cells and demonstrate how the motor can be turned on and off with the circuit thus far.

10. Remove the cells and connect a clip lead to the spring that jumpers the two cells together (at the "back" of the holder, opposite the connections to its leads). The other end of the clip lead goes to the other position of the switch. (If an "in-line" 2-cell holder is all that is available, this "tap" on the battery can be made by trapping the stripped end of a piece of hookup wire between the cells, the other end of this wire being screwed to the second position of the switch.)

11. Installing the cells now causes the motor to run at either of two speeds; the switch connects it to either one cell, or two in series.

12. A disadvantage of this circuit is that the motor cannot be turned off. Challenge the student, given the simple SPST switch, to devise a way of interrupting power to the motor. (The easiest place to do this is by disconnecting the motor from the negative battery lead and placing the new switch in series.)

13. If time permits, prepare for the next session by proceeding with winding the coil (to be described in Lesson IV).

Lesson IV

Electricity and Magnetism

A test coil was fabricated by the author for this session. (Actually, there is no reason why, if time permits, the students cannot make duplicate coils.)

The hookup wire from one of the Radio Shack reels (Cat. No. 287-1304) was removed and stored in a hand-wound bundle; the empty reel becomes the "coil form." This reel has a hub diameter of about 1-1/8 inches, and the flanges are about 5/8 of an inch apart.

"Magnet wire" (wire whose outer insulation is thin enamel) of 26-gauge is the most appropriate for the coil (Belden Wire Co. "Beldsol No. 8053").

In order to secure the wire, two tiny holes were drilled in one flange, one right near the hub and the other half-way out to the edge (a No. 55 drill was used). One end was put through the inner hole (inserting between the flanges), pulled out to about 8 inches, and secured inside the hub with tape. Six layers were neatly wound, wrapping tape around the winding every other layer to renew the coil form. When the sixth layer was finished, the far end of the coil was brought through the outer hole; then the two leads were twisted firmly so that they would hold each other in place. Finally, the pair of wires was brought through the center, and tape was neatly placed over them to relieve strain.

Like all enameled wire, it must be stripped with a knife or sandpaper. About one inch at each end was stripped bare. Besides being "solder soluble," the enamel on this material (Belden "Beldsol") strips easily with sanding.


1. Some small alnico permanent magnets.

2. Eighteen inches of flexible string.

3. Six-volt battery pack.

4. Either pre-wound coil, or 26-gauge magnet wire and the empty spool described above.

5. Patch cord with alligator clips, Radio Shack No. 42-2421.

6. Small tape recorder with monitor earphone, or Radio Shack Test Amplifier, No. 277-1008.

7. Small motor which can be destroyed.

8. An Audicator, if possible.


1. Show magnets attracting and repelling.

2. Hang a magnet on a piece of string and attempt to show that it operates as a compass.

3. Either with the pushbutton or just by intermittently touching its wires to the 6-volt battery, hold the coil just over a small magnet on the table and demonstrate that the magnet jumps up into it when it is energized.

4. Show how the screwdriver, running through the center of the coil, becomes a magnet when the coil is energized -- just strong enough to pick up steel pins and small screws.

5. An Audicator, connected across the coil, can be made to fluctuate in frequency as a magnet is tossed through the center of the coil.

6. An Audicator, when connected across a motor, makes silly noises when the motor shaft is spun; these noises are different for the two directions of rotation.

7. Using the patch cord, connect the coil to the input of a microphone amplifier of some sort, possibly a small tape recorder with an earphone in the monitor jack. Position the coil in front of a telephone earpiece (it must be a phone with an electromagnetic earpiece) and call someone; with this setup, a third party can listen, and the conversation can be recorded.

8. On various appliances, move the coil around -- twisting and turning it this way and that -- so as to find their sources of hum, buzz, or other electromagnetic noise. It will be especially fun to put this "pickup" coil near a battery motor, noting the increase in loudness of the buzz as the motor's shaft is loaded with pressure from a finger.

9. Using the screwdriver and/or the diagonal wire cutters to unfasten "crimps" in the case, take apart a small motor; salvage the magnet and unwind some wire from the armature.

Lesson V Codes -- Braille and Morse


1. A couple of sets of the students' notes on this subject, including the Braille alphabet generated with them.

2. [Note: As per the discussion in this lesson, the format of the Braille is critical. The patterns of Braille characters occur in cycles of ten. The first line should contain only the letters "a" through "j" (with spaces in between). Positioned directly under these should be "k" through "t." On the third line should be the letters "u v x y z"; the "w" being left out. On the fourth line, "w" should be placed below the space between "v" and "x." In this arrangement, it is easy to see how "a" is related to "k" and to "u"; likewise, "e" should be in a column with "o" and "z."

3. Skipping a line, the numbers are shown as:

4. "#1 #2 #3 ... #1995"

5. The bottom of the page may show a simple message in Grade I Braille; following my father's lead, the author's sentence reads: "even a goat does his best work with his head"

6. Braille slate and stylus, as well as paper. A $3 plastic set (a 4-line 28-cell plastic slate and stylus, Cat. No. AIL16S) is available from the NFB Materials Center, 1800 Johnson St., Baltimore, MD 21230; Phone: (410) 659-9314.

7. Pushbutton switch.

8. Some sort of buzzer or bell.

9. A telegraph key, if you can find one.

10. A beeper or Audicator as a high-quality sounder.

11. An honest-to-Pete ham-radio operator, volunteering to represent the local radio club.


1. Show the system of Braille as it develops throughout the alphabet; point out that the "W" does not fit the system.

2. Next, demonstrate that the Morse Code is predicated on a different system -- the most-used letters being the shortest.

3. Build a telegraph set, either with the pushbutton and door bell or with more sophisticated equipment.

4. Sending messages over one wire can be illustrated by using a long stretch of magnet wire for one conductor, and using ground returns of water pipes for the other. (More cells may have to be stacked in series in order to make this work.)

5. If there is a ham-radio operator afoot, produce him so that he can extol the virtues of the hobby.

Lesson VI


Because of my 35-year involvement in the field of electronics, I had a lot of junk to enrich others' garages. Military field phones, the electromagnets from doorbells, and oddments of switches were some notable examples. Without this, however, there is plenty which could be explored.

Proposed Activities

1. A question-and-answer period is an obvious fallback.

2. A detailed discussion of a dead computer board or discarded consumer appliance would be fruitful.

3. A recorded extemporaneous radio play could be held, using sound effects (doorbells and telephone calls, not to mention dentist-drill-sounding motors) as props.

4. A field trip to a hardware store or electrical shop would be the author's strongest suggestion.

5. Among the community of ham-radio operators, there are pack rats who could easily part with items to be dismantled, and such "big brothers and sisters" exist as to adopt the young enthusiasts.

Additions and New Activities

The author's most fruitful contact for surplus equipment was to the George S. Lad Chapter of the Telephone Pioneers (there will be a Telephone Pioneers chapter in your area). One phone call got me a box of rotary-dial telephones, the uses of which are described below in "Supplemental Activities."

Private donations for the materials were easy to get, and the students were thus able to keep the tools and project materials.

Supplemental Activities

(Note: These have been demonstrated at the 1995 conference of the California Transcribers and Educators of the Visually Handicapped, and not yet presented in classroom sessions.)

Magnet Chase:

Very strong bar magnets are available for $10 each from Edmond Scientific (Cat. No. 31,101). Called "cow magnets," they are intended for ingestion by cows, where they trap bits of bailing wire that invariably find their way into the hay. The fact that they are smooth and round makes them ideal for rolling magnet games -- making them chase or find each other (by repulsion or attraction) on a table top.

If a table with a fairly thin top can be found (5/8th inch or thinner is ideal, 1 inch is acceptable), two cow magnets will exhibit sufficient attraction so that one on top of the table will follow one being manipulated underneath. Imagine a group of players around the table (sighted players being blindfolded) trying to catch the top magnet, while a player underneath the table tries to anticipate their moves in an attempt to keep the magnet away from them.

Perhaps each player who successfully captures the magnet must drop out, leaving remaining players to try for it. A reward might be that the first to make the catch become the next one to manipulate the magnet underneath.

Besides being good fun, this would strengthen children's ability to localize and reach for a moving target.

Building a Local Telephone Network:

A number of surplus telephones were procured from our local (George S. Lad) chapter of the Telephone Pioneers. As many as six at a time were powered by a single 12-volt lantern battery as follows:

Six telephone junction boxes with modular jacks, Radio Shack 279-355, were mounted side by side on a 14-inch piece of "1 by 2" scrap wood. Yellow and black wires were not used; all the green wires were jumpered together, and all the red ones were jumpered together. The negative of the 12-volt battery goes to the green wires, while the positive battery terminal goes through a 360-ohm 1-watt resistor (DigiKey 360W-1-ND) to the red wires. (A series hookup would be more typical of telephone networks, but this parallel arrangement means that parties can talk even though some of the phones are hung up. The disadvantage is that more battery current is drawn as more phones are picked up.

Selective dialing within the loop would take a complexity of circuitry that was not attempted. However, "ringer dynamos" can be found in science equipment catalogs from time to time, and direct parallel connection of one of these can ring all of the phones as long as all are hung up.

Thus, if there are close friends living in an arrangement where a 2-wire line can be run between their rooms, it would be possible for them to have their own telephone system. In that case, either a series connection, or the parallel connection shown, will work. The battery can be at any location.

If each party has his own battery, with his own 360-ohm resistor in series with an on/off switch, the parties can signal each other. With this arrangement, all phones are left off the hook and the battery switches are turned off.

Any party wishing to signal the others can turn his switch on and off several times in hopes that those hearing clicks from the receiver will pick up and talk.

Listening to the Radio Through the Telephone:

A simple adapter can be soldered together to allow plugging the telephone into the earphone output of any radio or tape recorder. The red and green wires from a telephone jack go to "tip" and "sleeve" connections of a suitable earphone plug. (A Stereo Miniplug, Radio Shack 274-1547, with the "ring" connection left open, is recommended so that a stereo Walkman-type device can be used without fear of damaging it by shorting out its right channel with a single-circuit plug.)

Extra modular jacks are available from DigiKey Corp. (Cat. No. 9011-ND). (The modular jacks in Radio Shack junction boxes can be used, but these assemblies are more expensive; moreover, the "spade lugs" on the ends of the wires must be snipped off to permit soldering the wires to the plugs.)

Address List

Belden Wire and Cable Co., PO Box 1980, Richmond, Indiana 47375: Phone: (800) 235-3361.)

Digi-Key Corp., P.O. Box 677, Thief River Falls, MN 56701 Tel: (800) 344-4539

Edmond Scientific, 101 East Gloucester Pike, Barrington, NJ 08007; Phone: 609-573-6250

NFB Materials Center, 1800 Johnson St., Baltimore, MD 21230; Phone: (410) 659-9314.











1. A battery is made up of cells; a 9-volt battery contains six 1.5-volt cells.

2. It is not technically proper to speak of a size D cell as a flashlight battery. More properly, a flashlight's battery contains two flashlight cells (or more, depending on the flashlight).


1. The capacity of a cell or battery is measured in "ampere-hours" (abbreviated "amp-hours" or "AH"). This means amps times hours; 2 amps times 5 hours is 10 amp-hours.

1. An alkaline D cell is rated at 10AH. This means that it could supply 10 amps for 1 hour, 5 amps for 2 hours, 1 amp for 10 hours, and so on.

2. I have a radio which draws 1/10 amp from its two D cells. How long will its batteries last?

3. First of all, to say it has "batteries" is improper; the radio's "battery" is made up of two D cells. It is okay to talk about the life of its cells or the life of its "battery," but it is not proper to speak of its "batteries."

4. The life of the cells will be 100 hours; 1/10 amp times 100 hours is 10 amp-hours.


1. If you can afford them, alkaline cells are becoming standard, and they are the best kind.

1. Their amp-hour rating is high; they last the longest.

2. Their shelf life is very long; they are almost as good as new after one year on the store shelf.

3. They almost never leak into your equipment.

2. The cheaper kind are called "zinc-carbon" cells.

1. Their amp-hour rating is about 1/4th that of alkaline ones -- but there is a catch:

1. Zinc-carbon cells work best under light loads, such as radios with earphones and battery clocks. Under heavy loads, such as flashlights and tape recorders, these cells appear to run down very quickly; they come back to life, somewhat, if they are allowed to rest. (Hydrogen bubbles develop inside which make them seem like they're dead, but resting them allows these bubbles to fizzle out -- the cells will come back to life somewhat.)

2. When they run down under the best conditions -- under a light load -- they eat through their metal outer shell and leak goop into your equipment. They can also leak just sitting there, so take zinc-carbon cells out of things you are not using.

3. The shelf life of zinc-carbon cells is not very long; after one year, they are about half gone.

3. The most common rechargeable cells are called "nickel-cadmium." These can be used over and over again, recharging them from a battery charger when they go dead.

1. Their amp-hour rating is about 1/4th that of alkaline cells.

2. They work well under heavy loads.

3. Their shelf life is very poor; even when they are new, they are almost dead after six months of sitting around. When they become older, their shelf life can be as short as a couple of weeks.

4. They like to be used. You should only buy them for things that you use a lot -- a favorite tape recorder or radio. When they are left to sit around, they often go bad, and have to be replaced.


1. Alkaline Type

1. D Cell: 10AH

2. C Cell: 4AH

3. AA Cell: 2AH

4. 9-Volt Battery: 1/2AH

2. Zinc-Carbon type (Note: These figures are only "sort of" right; how long they work depends on what kind of thing they are running -- in other words, whether their load is heavy or light.)

1. D Cell: 2AH to 5AH

2. C Cell: 1AH to 2AH

3. AA Cell: about 1/2AH

3. Nickel-Cadmium type:

1. D Cell: 2.5AH

2. C Cell: 1AH

3. AA Cell: 1/2AH

4. 9-Volt Battery: 1/5AH




1. When pouring liquids (especially hot liquids), blind people sometimes use an electronic alarm to tell when the liquid is almost to the top of the cup. It makes a sound which tells them to stop; by making an electronic sound, it "says when."

2. It has three parts: a 6-volt battery (made of four 1.5-volt cells), an electronic noise maker (a Radio Shack Chime, No. 273-071), and a liquid-level sensor (two wire buck teeth which hook over the edge of the cup).

1. When water hits the buck teeth, electric current flows in the water.

2. The Radio Shack chime used has a control line, its white wire, which rings the buzzer from very little electric current -- just the sort of thing that happens when water hits the buck teeth.


1. We will use a kind of wiring called "breadboarding." Using a piece of wood -- one just like is used in the kitchen for working bread dough -- everything will be screwed down with wood screws.

1. First, the parts will be screwed to the wood (this is called "mounting" them).

2. Next, the connecting wires will be wrapped around screws which are then tightened down to hold them together.

2. B. Breadboarding circuits has two advantages over other systems of building things.

1. One other way people build circuits is by "soldering" the wires together -- although blind people do "soldering," it is dangerously hot and takes practice. (Soldering means joining wires with molten metal; a very hot tool which can melt the metal is a dangerous thing to have around.)

2. Since everything, even the wires, are just screwed together, things can be changed around easily, and even new things can be built on the breadboard.


1. First, two of the things, the battery holder and the chime, are mounted on the board:

1. The battery holder is held down by screws in its corners.

2. The chime has two little fins with screw holes.

3. These should be placed near each other so that their wires reach, but not so close together that making connections of their wires is too crowded to be comfortable.

2. Second, wires must be attached to the buck teeth (this little thing being called the "sensor").

1. First, insulation is "stripped" off the ends of the wires; this is done with a tool called "a pair of wire strippers."

2. Notice that the sensor has two screws with extra nuts which can be first loosened, then tightened down again on the ends of the wires. (The wires are wrapped around the screws under the nuts, and then the nuts are tightened onto them.)

3. After two wires have been attached, they are twisted together to make what is called a "cable" (a cable being a bundle of two or more wires).

3. All the rest of the connections are made using screws on the breadboard, and they are listed as follows:

1. The black wire from the battery holder -- the one which goes to a spring -- goes to the black wire of the chime.

2. The red wire of the battery holder goes to the red wire of the chime; this connection also goes to one of the wires of the sensor.

3. The white wire of the chime goes to the other wire of the sensor.


1. First, put in the four cells which make up the battery.

2. Next, with a test lead (one having a test clip on each end), "short out" the buck teeth (meaning, connect them together with this test lead). The chime should ring.

3. Once you know it works with the test lead, it's time to try it in a glass of water. Place the sensor on the rim of the glass -- with the buck teeth inside -- and fill the glass with water. As soon as the water touches both teeth, the chime should ring.

Alternative Circuit Using the Sonalert:

If the above chime is not available, this circuit will do, and it is less expensive. The Radio Shack part number for the Sonalert is 273-060, and a Digi Key equivalent is a P9928-ND.

The 4-cell battery holder is used. The black wire of the battery goes to the black wire of the sounder. The red wire of the battery goes to one wire of the sensor. The other wire of the sensor goes to the red wire of the sounder.




1. Most of the time, switches have pieces of metal which touch each other when an electric circuit is "turned on." (Some switches do not have moving parts; for example, transistors are often used as switches.)

1. "Closing" a switch is how you turn something on -- when those pieces of metal are touching, the switch is said to be "closed," and current can flow through it.

2. "Opening" a switch, separating its pieces of metal, interrupts the current and turns the circuit off.

2. Switches are usually classified as to the number of circuits they can handle, and by the number of "on" positions they have:

1. The simplest switch has just two contacts. These are put "in series" with a circuit which you want to turn on and off. They can be flipped in either of two positions -- either "off" or "on."

1. This simple switch can control only one circuit; it is therefore said to have a "single pole" (SP).

2. "Throwing" the switch to off or on is all you can do with it. This single "on" position classifies it as "single-throw" (ST).

3. Thus, having a single pole and only one position to throw on, this simplest switch is called "single-pole single-throw" (SPST). This would be the kind of switch you would use to turn on a light, or to turn on your stereo system.

2. A little more complicated, there are switches with a piece of metal which can be made to touch either of two other contacts. Such a switch could either turn one thing on, or another thing on.

1. This switch may still have only one pole (SP) -- one piece of metal (perhaps going to the positive of the battery) can swing this way or that to touch another contact.

2. This switch has two different "on" positions; it can be thrown this way or that. It is said to be "double-throw" (DT).

3. The classification for this switch is "single-pole double-throw" (SPDT). Such a switch might be used to select either AM or FM on your AM/FM radio.

3. There are units containing two or more switches, operating them from a single lever. Each of these switches is called a "pole." A double-pole switch can operate two completely separate circuits. For example, a DPST (double-pole single-throw) switch could be used to turn your stereo speakers off -- something you would need if you wanted to use earphones. A DPDT switch (double-pole double-throw) could be used to throw one set of speakers "on," or another set of speakers (in another room) "on." You need two poles, one for the left channel and one for the right.

4. What would you use a double-pole 4-throw switch for? On stereo systems, for example, there is often a switch to select inputs: "phonograph," "radio," "tape," and "auxiliary." You need two poles because of stereo -- one for the left channel and one for the right.

5. Pushbutton switches have two more things to define. The doorbell button, and the button inside the refrigerator door which controls the light, are both SPST, but they are very different.

1. The doorbell button is "normally open;" pushing this button "closes" the switch and rings the bell.

2. The refrigerator switch is "normally closed;" closing the door on it (which pushes the button) turns off the light. If this pushbutton were used on your doorbell, the doorbell would be ringing all the time until the mailman came and interrupted it by pushing it.

3. A single-pole double-throw pushbutton can be connected as normally open or normally closed; it has two "on" positions, one when the button is pressed, and the other when it is released.


1. Switches are always connected "in series" with their circuits.

1. "In series" means that, as you trace your finger around a circuit, you see one thing, then another, and another. For example, if you have a battery-operated light with an SPST switch to turn it on and off, the hookup would be as follows:

1. One battery terminal goes to one side of the switch; the other side of the switch goes to one side of the light, and the other side of the light goes to the other battery terminal.

2. Another way of saying this is: One battery terminal goes through the switch, then through the light to the other side of the battery.

3. Another way of saying it: The switch and the light are in series, and this series combination goes across the battery.

2. Except in rare cases, switches don't go across anything. You should never connect a switch "across" the battery (one switch terminal going to one side of the battery, and the other switch terminal going to the other side of the battery). If you did this, closing the switch would be known as a "short circuit" -- things would heat up, you would kill your battery, and the switch might burn out.

2. The following examples show the use of double-throw switches. Note the use of the term "swinger" in these examples. The "swinger" is the piece of metal that flips between one "on" position and the other.

1. Suppose we want to switch between a light and a doorbell, both of which run on 6 volts. First, a battery of 6 volts will be assembled by stacking four 1.5 volt cells in series. Next, we will connect the positive side of the battery to the swinger of an SPDT switch. One "on" position of this switch will go to one side of the light; the other side of the light will go to the negative of the battery. The other "on" position of the switch will go to one side of the bell; the other side of the bell goes to the negative side of the battery.

2. Unless we have a special SPDT switch that has an "off" position -- and some do -- either one or the other will be on all the time. We can buy an SPDT switch with a "center off" position, as it is called, or we can put another SPST switch in series with the system.


4. To put in the new on-off switch, we can cut the wire which goes from the positive of the battery to the swinger of our first switch, then install the SPST one where this cut was made.

5. Suppose we get a new set of small speakers which would be lovely for the kitchen. With a DPDT switch, we could arrange to switch over to these speakers; the main living room set would go silent, so someone could be watching TV while we listen to stereo in the kitchen.

6. On the left channel, one side of one big speaker and one side of one little speaker both go to the black left-channel terminal on the amplifier. One pole of the switch will take care of the left channel; the swinger of this pole will go to the red output terminal. The other side of the big speaker will go to the upward "on" position of this pole, while the free end of the little speaker will go to the downward "on" position.

7. Likewise, on the right channel, one side of each speaker goes to the black output terminal. The red output terminal goes to the swinger of the other pole on the switch. The upward position of this pole goes to the free end of the big speaker, while the downward position goes to the free end of the small speaker.




1. Nobody quite has an explanation for what "magnetism" is, but we do know what it's caused by -- moving electrons.

1. As you know, atoms have electrons whizzing around them all the time, sort of like planets whizzing around their star. Does this mean that atoms are magnets? Yes, or at least each electron's orbit has a magnetic field.

2. There are metals whose atoms can be organized so that at least one of their electrons is orbiting in the same direction as an electron of neighboring atoms.

1. These metals are usually heavy ones -- iron, nickel, and cobalt, for example. Lighter metals, such as copper and aluminum, are so disorganized as to refuse to respond to magnetism.

2. There are highly crystalline materials which can store magnetism; their atoms can be locked into position within unforgiving crystals. Atoms in these materials will stay in position until something comes along to knock them out. (Hitting a magnet with a hammer will take some of the magnetism away; heating, so as to stir up the atoms, will also demagnetize a magnet.) So-called "permanent magnets" are usually made of a crystalline alloy of aluminum, nickel, and cobalt; this material is called "alnico." Before alnico magnets, permanent magnets were made out of hard steel.

3. Those two kinds of materials are very different: Soft iron (whose crystal of atoms is not very rigid) strongly attracts magnets, but this iron forgets its magnetism when the magnetic field is removed. Materials like alnico and steel "remember" what kinds of magnetic fields they have been in. Remember these differences (known as "magnetic properties"); we will have need for metals which remember and metals which forget.

2. Magnets strongly react to other magnets.

1. The "directional compass" is the most famous example of this: It so happens that the earth is a big magnet. If you hang a bar-shaped magnet on a string, it will turn to face in a north-south direction. The end of your magnet which wants to point north is called the "north-seeking pole" (called the "north pole" for short); the end of your magnet which is drawn southward is called the "south-seeking pole" (the "south pole" for short).

2. The rules are: "Opposite poles attract," and "Like poles repel."

1. If you bring the north pole of one magnet near the south pole of another, they will eagerly go for each other, pulling so as to get together.

2. If you try to bring the north pole of one magnet over to the north pole of another, the magnets will "repel" (push apart) so as to get away from each other.


1. In 1820, a fellow named Oersted was determined to prove to a group of scientists that there was no connection between electricity and magnetism. To show that there was none, he used a compass as a "magnetism detector." He reasoned that if he put the compass near a wire which was carrying electricity, any magnetic field that might be caused by the electricity would throw the compass needle off course. If he tried this and the compass stayed pointing north, he would prove that there was no connection between the two subjects.

2. Standing there in front of everybody -- oops! The needle moved because of the flow of electricity. The fact that they are truly connected is the most important principle of electricity and electronics.

3. Electromagnetism:

1. Every wire that carries an electric current generates magnetism. You can gather this magnetic force together in a strong bundle by wrapping this wire into a coil. If you wrap a coil of wire around a nail, the nail will become a strong magnet when you connect the coil of wire across a battery. (If the nail you use is made of steel, it will "remember" some of the magnetism when you disconnect the battery. If it is made of soft iron, as soon as the battery is disconnected it will forget that it was a magnet and drop whatever it is holding.)

2. Whenever a wire is moved through a magnetic field, electricity is generated in it. For example, picture a horseshoe-shaped magnet; whenever you pass a wire between the poles of the magnet, a voltage develops between the wire's ends; how high this voltage is depends on how fast you pass the wire between the poles of the magnet. Furthermore, you can "generate" lots of electricity by wrapping this wire into a coil, then spinning this coil -- end over end -- between the magnet's poles.

3. Electric motors contain some way of getting a stationary magnetic field (some types containing permanent magnets, and others containing "electromagnets"), and coils which can spin within this magnetic field. When power is connected, the coils which can spin try to find a magnetic home for themselves, but the joke is on them, for all motors have some way of changing things around in the nick of time so that the spinning coils keep searching, searching, searching for a friendly opposite magnetic pole.

4. Some kinds of motors -- when you spin them by way of a windmill or a steam engine -- make electricity. By making them spin, their moving coils are made to go around in a magnetic field, and this "generates" electricity. Even the little motors found in toys can be used in both ways: you can use electricity to make them run, or you can run them to make electricity.


1. Something easy to watch work is a door buzzer (or a doorbell which works on the same principle as a buzzer, not a fancy door chime). Inside these is a coil (sometimes two coils) wound around soft iron; this makes up an electromagnet which is very strong when power is applied, but whose soft iron forgets about magnetism when power is removed.

2. Alongside this electromagnet is a spring lever. When power is applied, the lever is drawn toward the magnet. Just as the lever is about to find the electromagnet, though, a switch on the back of this lever opens and cuts the power. When the switch opens, the lever's spring pulls it back, only to close the switch and cause the magnet to pull in on the lever again.

3. Highly confused, the poor lever bounces back and forth, never quite happy with its situation. The buzzing you hear is the lever flapping back and forth; the end of this lever may be used to bang on a bell.

4. A "loudspeaker" is actually a special kind of "motor." It contains a strong magnet, as well as a coil of wire which can move. This coil is mounted on a paper cone; the cone is supposed to push air back and forth to make sound waves.

5. If you connect a battery to the coil in one direction, the paper cone will jump out toward you; the coil is trying to get away from the magnet. If you turn the battery around, the coil will pull the paper cone away from you.

6. It is necessary to drive a loudspeaker with an amplifier. What comes out of the amplifier is a strong electric current which moves back and forth in accordance with sound waves.

7. Just as a motor can be used in a backwards way to make electricity, a loudspeaker can be used to make electrical sound waves. If you talk at the paper cone, the moving coil will "generate" electricity; the speaker becomes a "microphone." One kind of microphone -- the so-called "magnetic," or "dynamic," microphone -- is nothing more than a little speaker being used backwards. Earphones are just little speakers too, and they make fine microphones too.

8. Induction:

1. Any coil in a changing magnetic field will generate electricity. You can move a magnet in the coil, or move the coil inside a magnet -- all the same, you get electricity out of the coil. But what happens if you "sniff around" an electromagnet with another coil? A neat thing to have would be a coil made of 200 turns of so-called "magnet wire" (a very thin wire with enamel insulation on it); then we could do some experiments.

2. If a nearby electromagnet has a changing electric current in it, the changing magnetic field will generate electricity in our test coil. If we connect our coil to a set of earphones, and then bring it near that doorbell mentioned earlier, we will hear the magnetic field of the electromagnet being turned on and off.

3. Another neat trick is to connect our test coil to the microphone input of a tape recorder. With this setup, you can hear all kinds of magnetic fields. For example, by just moving around the room, you can record the "hum" of electrical appliances, all of which generate varying magnetic fields as they use "alternating current" (AC) electricity from the wall sockets.

4. Now, put the test coil in front of a radio's loudspeaker. You will find that you can record the radio just fine by "sniffing" out the changing magnetic field in the speaker.

5. By putting the test coil near the earpiece of a telephone, you can record telephone conversations, just by "sniffing" the changing magnetic field made by the earpiece.

6. This "sniffing" of changing magnetic fields is called "induction." The electricity in our test coil is said to be "induced" by the magnetic fields.

9. Transformers:

1. Transformers are just coils which are placed next to each other. One is driven by AC (alternating current) and becomes an electromagnet. The other "sniffs" the magnetic field of the first, and a voltage is "generated" in it.

2. If the electromagnet one (called the "primary winding") has 100 turns, and the second coil (called the "secondary winding") has 10 times that many, the voltage on the "secondary" will be ten times as high as what you put in on the "primary."

3. An electric train is made to run off about 18 volts. Yet, we get 117 volts from the wall socket. What do we need to run the train?

4. The answer is a transformer which "steps down" the voltage from 117 volts to 18 volts. 117/18 equals 6.5, and therefore the primary winding has to have 6-1/2 times as many turns as the secondary.

5. The catch is, you can't run a transformer off batteries. The reason why is that a battery provides a steady current in only one direction. (This is called "direct current" or DC.) Connecting a battery to the primary winding of a transformer will make an electromagnet out of it, all right, but electricity will only be generated in the secondary winding when this magnetic field is changing.

6. Therefore, transformers only work on AC (alternating current, such as comes from the wall socket). They do not do anything (except maybe burn out) when connected to DC (direct current, such as comes from a battery).




1. Idea Codes:

1. Chinese writing, for example, comes from a set of pictures that represent things and ideas.

1. This means that they need thousands of symbols, one for each idea or thing.

2. The advantage is that you don't have to speak Chinese to read it; Japanese people can stumble through a Chinese newspaper, even though the Japanese language is completely different.

2. A set of thousands of symbols, like Chinese writing, does not fit very well with machines.

1. Any keyboard, as for a typewriter or computer, turns out to be terribly complicated.

2. Making a "Braille machine" that could make raised pictures of these characters is very hard to do, and some of these characters are hard to tell apart by feel.

2. Phonetic Codes:

1. Although our alphabet came from an ancient "idea code" of the Phoenicians, the Greeks and Romans made a code out of it which would represent the sounds of our languages.

1. The advantage is that we have very few symbols (we use only 26 in English).

2. Having only 26 symbols, we can make up different codes which mean the same things.

3. Examples of these "new" codes are Braille and Morse Code. Though symbols of these codes look nothing like the symbols of print, they still work; "B" "A" "L" "L" spells "BALL" in Morse Code, Braille or "finger spelling" for the deaf.


1. Braille is a systematic code.

1. Over 175 years ago, between the ages of 12 and 15 years, a young inventor named Louis Braille invented a 6-dot code for our alphabet which is much easier to feel than the curlicues of print. (He really made up only 25 letters; the French don't use the "W.")

2. To make up this code, young Louis just made up the first 10 letters ("A" through "J"); then he modified these by adding one dot below them to get the next 10 ("K" through "T"). Finally, he put two dots below the first 10 letters to get the remaining 5 ("U," "V," "X," "Y," and "Z").

1. Everything is based on the first 10 characters, "A" through "J"; even the numbers are the same as these letters, modified with a "number sign" in front of them. A number sign followed by "A" "I" "H" "G" makes up the number "1987."

2. The disadvantage is that a letter that you use a lot may have quite a few dots. For example, in our language, the letter "T" happens quite often, but the Braille Code for "T" takes four dots; the letter "J" appears much less often, but the Braille Code for "J" is only three dots.

3. A Braille alphabet has been attached to these notes. The first three lines show the alphabet as I have described it. The top line shows Braille's basic combinations. The second line is different from the first by adding one dot to each character. The third line shows how two dots were added to get the last five French letters. Notice that the "W" is off by itself; it was invented by the English as an afterthought, and does not follow Braille's system.

2. Morse Code is a different system:

1. With the invention of the "Telegraph" (in the 1840s), Samuel Morse invented his code which could be sent along wires by pressing a simple pushbutton switch on and off.

1. At first, he made a receiving device with a pen which dropped onto a moving strip of paper when the switch was closed. (The marks made by the pen were either "dots" or "dashes," depending on how long the switch was held closed.)

2. Later, it was discovered that the operators who could read the code were getting messages faster by just listening to the pen bouncing up and down; the receiving device was changed to a "sounder" which made noises instead of drawing on paper.

2. To make his Code as short as possible, Morse looked through some newspapers and wrote down the "frequency of use" of each letter. Since "E" is the most-used letter, he made his code represent it with only one "dot." Since "T" is the next most-used, he represented it with only one "dash." He continued on until he got to letters which are seldom used: a "J" is represented by one "dot" and three "dashes."

1. Although harder to learn than Braille, the "Morse Code" is very efficient; the most-used letters go by very quickly, and the least-used ones (which take longer to send) are seldom heard.

2. If Braille had imagined this, writing Braille, dot by dot, would be much faster than it is today.

3. The following is a list of Morse's symbols -- his alphabet. As you see them written here, try to imagine them by the sounds they would make ("dit's" for periods and "dah's" for dashes). Eventually, you will be listening to the sounds of a tone going "dit" or "dah." Therefore, when you see the symbol _ . _ . (the letter "C"), it should bring to mind the sound "dah dit dah dit."


1. The simplest set is made of a battery, a buzzer and a pushbutton (normally open) switch.

1. The pushbutton is usually quite fancy, having two adjustments -- one for the distance you can push it (supposed to be 1/8 inch), and the other adjustment for the spring tension (set for 2 to 6 ounces). This switch even has a fancy name; it is called a "telegraph key."

2. The "sounder" can either be an electromagnetic buzzer, or an electronic oscillator.

2. The components are connected in series; that is, the positive of the battery goes through the telegraph key to one side of the sounder, while the other side of the sounder goes to the negative of the battery.



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In my college physics class, I remember the niftiest experiment -- using a tuning fork as a "wavelength" standard to excite an adjustable column of air in a pipe. The pronounced audible indications make this experiment "fun to run," and it is a good demonstration of resonant systems.

Statement of the Principle

Like a quarter-wave radio antenna, a quarter-wave pipe with one closed end exhibits its primary resonance by reflecting the wave back to the source from the closed opposite end. A "null" in the motion of the sound wave occurs at the closed end; maximum motion of the air occurs at the open end. The total distance that sound travels -- down the pipe and back again -- is one-half wavelength. Other resonant points can be found at each additional half-wavelength down the pipe. (The "Q" of the resonator is less for each added length, so that the audible effect is much less pronounced for longer column lengths.)

Description of the Apparatus

The apparatus is a vertical pipe whose bottom end is connected, by a flexible hose, to a reservoir of water which can be raised and lowered. The reservoir, a container whose diameter is much larger than that of the pipe, is used to set the level of water; the length of pipe above the water level thus becomes a tunable resonator.

[The bizarre nature of this apparatus has earned it the nickname "the water organ." The water itself is not involved in the resonant system; water in the pipe is just a cute way of making an adjustable plunger. Any gigantic slide-whistle type arrangement would work.]

A tuning fork is excited and positioned so that the ends of its tines are directly over the open end of the pipe. Then, the water level is manipulated.

As the water level passes through points of resonance -- creating air columns of 1/4th- 3/4th- and 5/4th wavelength -- the sound of the vibrating fork is re-enforced and amplified, giving audible indications of resonant points.

As much as I remember in physics lab: A glass pipe was held vertically. A hose connected the bottom of the pipe to a fitting on the bottom of a fruit-juice can. One team member hit the fork on his shoe and held it over the top of the pipe. Another moved the juice can up and down, fishing for peaks in the sound level. The third was busy with a meter stick -- measuring the difference in water level between resonant points. We were busier than a one-armed wallpaper hanger.

One person could run this mess if it were mounted some way. My fortunate circumstance is that, working around laboratories, I am able to borrow a "ring stand" with all sorts of rods and clamps; this makes assembly of the system a snap. However, some sort of wooden upright (preferably five feet tall) would do for mounting the pipe and associated items.

For convenience, I recommend affixing the tuning fork to the structure. Its maximum output is a "lobe" between the tines, close to their free ends; thus, the fork should be positioned horizontally, the tips being as close to the top of the pipe as you dare. A rubber mallet is then used to excite it; a home-made one can be fashioned by mounting a hard rubber ball on a piece of dowelling.

A ready source for the tuning fork is Player Piano Company, 704 East Douglas, Wichita, KS 67202; Phone: (316) 263-3241. The one they stock, Cat. No. 1100, is the standard pitch for A, 440 Hz (440 cycles per second).

How you wish to handle the reservoir is a matter of choice. You can just lift it up and down "free hand." I hung mine by a loop of string attached to a clamp which could be tightened at any height. An added frill is affixing a Braille yardstick to the structure to afford precise measurement of the water level. Remember, the water level changes within the reservoir. Therefore, proper measurement is not the position of the container or a movable clamp; you must measure the position of the top of the water, which will be the same in the reservoir as it is in the pipe.

A good home-made yardstick can be Brailled on labeling tape using the one-line Dymo slate, Cat. No. 23-2001-8, manufactured by Howe Press, 175 North, Beacon St., Watertown, MA 02172. A good feature of this slate is that its inter-cell spacing is set to 1/4th inch; unusual for dimensions of Braille equipment. Thus, a mark made in dots 1-2-3 of the last cell is six inches from dots 1-2-3 of the first cell. (Other slates, even those from Howe Press, are not made to match markings on a rule; somebody decided that this slate would be a nice piece of shop equipment to have around.)

Much of what I needed came from a hardware store with a modest selection of plumbing supplies. The pipe I used was a 40-inch length of PVC of 3/4-inch inside diameter. Starting with a glue-on fixture at the bottom, I went through a couple of "reducers" until I got to a screw-in "nipple" (1/4-inch Inside diameter). This nipple had an outer diameter of about 1/2-inch -- something I could force-fit with half-inch flexible tubing.

My reservoir was an up-side-down plastic one-liter soda-water bottle. At Walgreen's Drugstore, I found a reusable bottle stopper, one with a pull-up top that permits pouring without unscrewing it from the bottle. Conveniently, if the pull-up bit is forced to come completely off, what's left is a screw-on cap with a nice nipple which also fits the one-half-inch flexible hose. (There is very small printing on this stopper -- "CREATIVE PKG, ILLINOIS.")

About the reservoir, its contents must be sufficient to fill the hose and most of the pipe. This is accomplished by choosing a container of a large diameter compared to that of the pipe. My one-liter bottle (no longer able to hold one liter because about an inch of the bottom was cut off, and holes for my string hanger robbed me of another half inch, still left me with plenty of water in reserve. (The pipe holds a maximum of 17.7 cubic inches -- the volume in the bottle approaches 50 cubic inches.)

Performing the Experiment

The speed of sound is about 1125 feet per second at 20 deg.C. The tuning fork generates a sound of 440 cycles per second. Dividing "feet per second" by "cycles per second" (the seconds cancel), we get a figure of "feet per cycle"; 1125.4 over 440 equals 2.56 feet for a full wavelength. The first resonant point will be where there is a quarter-wavelength of air in the pipe, which is 0.64 feet -- 7.7 inches (approximately 7-11/16 inches).

The next resonance will be found by adding another half-wavelength -- lowering the water 15-3/8 inches (which will put the water level 1.92 feet from the top of the pipe).

The last resonance attainable with this length of pipe is five quarter-waves down the pipe; 2.56 feet times 5/4th equals 3.2 feet from the top of the pipe. If the experiment works, we hope that the distance of one wavelength is 30-3/4 inches, measured between the first and third resonant points.