SKTF -- Fall 1993

The Smith-Kettlewell Technical File

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

William Gerrey, Editor

Issue: SKTF -- Fall 1993

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 Details regarding products, suppliers, and other contact information are original and may be outdated.

Questions about this archive can be sent to











These chips allow two binary numbers to be

Outputs indicate whether one is less than, equal

to, or greater than the other. Singly, these chips compare
4-bit numbers;
however, they can be cascaded to accommodate

large numbers.
Applications would include comparing a counter

with the output of
an A-to-D converter. Suppose you run a stepper

motor from the
clock of the counter; you could get to stop, or

change direction,
as directed by the A-to-D converter's output.

The Motorola

Two 4-bit "words," "A" and "B," are fed to
four inputs. As they define them, these inputs are: A0, A1, A2, A3,
and B0, B1, B2 B3.
(The editor prefers to think of these inputs as
A1, A2, A4, A8,
etc., but the notation is arbitrary.)

There are three outputs: "A less than B," "A

equals B," and "A
greater than B." The appropriate output goes

high for its given

There are three inputs used for cascading:

"A less than B," "A
equals B," and "A greater than B." For some

obscure reason, on
the least-significant chip, these are to be tied

"low," "high,"
and "low," respectively. On the other hand,

"less than," "equal
to," and "greater than" inputs of each

higher-order chip go
directly to those corresponding outputs of its

neighbor. (If only one chip is used, these

inputs are still to
be committed with "equals" being high and the

others low.)

As you might expect, the outputs of the

highest-order chip are
the ones you pay attention to for the ultimate


[The truth table describing the operation of

those cascading
inputs suggest that the "greater than" one is a

dead pin. If you
think about it, the chip could learn anything it

needs to know by
responding to states of the first two. A

frequent entry in the
truth table for the "greater than" input is

"don't care."
Another source of literature, "The CMOS Pocket

Guide," says to
tie the "greater than" input high, as in low

high high. One of
us ought to leave it open some time and see what

doesn't smoke.]

Specifications for the


These are CMOS devices. Their supply voltage

can be between 3V
and 18V. In quiescence, and without a load, the

current drain is
minuscule--0.005uA typical, 5uA maximum. (As

devoted students of
the article "Inside Gates" will remember, SKTF,

Summer 1981,
current drain of CMOS logic goes way up in

operation, since
complementary FET's simultaneously conduct while

changing state.)

Their outputs can drive two low-power TTL

inputs, or one low-
power Schottky input. (This means sinking


As far as speed is concerned, they give a

figure called "turn-
on/turn-off delay time." This is the time

measured from when an
input line is half-way up and the time when the

output state is
half-way up. It varies considerably with power

voltage--at 5V, the maximum time is 860

nanoseconds (ns). At
10V, this maximum is 180ns; at 15V it is 130ns.

They show
typical delays of half these values, but the

prudent engineer
would plan on a delay of a microsecond at 5


Pin Assignments for the Motorola

MC14585BCP (16-Pin Plastic Package)

  • Power Connections:
    • Pin 8--VSS (ground)
    • Pin 16--VDD
  • Four-bit Word Inputs (logic high

    defined as "1"):

    • Pin 10--Input A0
    • Pin 7--Input A1
    • Pin 2--Input A2
    • Pin 15--Input A3
    • Pin 11--Input B0
    • Pin 9--Input B1
    • Pin 1--Input B2
    • Pin 14--Input B3
  • Inputs for Cascading chips

    (least-significant chip has pin 6 tied
    high; pins 4 and 5 are grounded):

    • Pin 5--Input A less than B
    • Pin 6--Input A equals B
    • Pin 4--Input A greater

      than B

  • Comparison outputs (go high when

    condition is met):

  • Pin 12--Output A less

    than B

  • Pin 3--Output A equals B
  • Pin 13--Output A greater

    than B

The CD4063

Once an RCA number, then made by Harris (and

who knows in six
months), this is a very similar device to the

above. They are
not pin-for-pin compatible, however.

As with the Motorola chip, the

least-significant device should
have its "cascading inputs" as follows: A less

than B low, A
equals B high, and A greater than B low. (This

input arrangement
holds true if a single chip is used.) In a

cascade of chips,
these inputs go to the corresponding outputs of

the less-
significant neighbor.

The sense of the 4-bit inputs is positive

logic--high equals 1.
The outputs: A less than B, A equals B, and A

greater than B, go
high when their condition is met.

Pin Assignments for the
CD4063 (16 pins)

  • Power Connections:
    • Pin 8--Ground
    • Pin 16--VDD
  • Four-Word Inputs (high equals


    • Pin 10--Input A0
    • Pin 12--Input A1
    • Pin 13--Input A2
    • Pin 15--Input A3
    • Pin 9--Input B0
    • Pin 11--Input B1
    • Pin 14--Input B2
    • Pin 1--B3
  • Cascading inputs (on

    least-significant chip, pins 2 and 4 are
    grounded; pin 3 is tied high):

    • Pin 2--Input A less than B
    • Pin 3--Input A equals B
    • Pin 4--Input A greater

      than B

  • Comparison Outputs (go high

    when condition is met):

  • Pin 7--Output A less than


  • Pin 6--Output A equals B
  • Pin 5--Output A greater

    than B



id="review" name="review">

by Jay Williams


As you may know, Radio Shack no longer sells

multimeter equipped with internal digitized

speech. It has been
replaced by the Micronta 22-182, which instead

provides an RS232C
serial port and associated PC-compatible

software. In addition
to voltage, current and resistance, this meter

can measure
capacitance and frequency. It also includes a

simple continuity
tester, a logic level indicator and a transistor

beta checker.


At $130, this is a good buy. However, if you

do a lot of work
with electronics, this meter should simply be

one more tool, not
your "be-all and end-all." For the blind

builder there is no
substitute for the traditional analog meter with

auditory output
when measuring dynamic parameters.

Readings can be displayed in several modes.

First, all
quantitative measurements can be displayed

relative to a
reference of your choice. Second, the meter can

be set to
register maximum and minimum readings, and

third, it can be set
to hold a reading indefinitely. Because you can

interface the
meter with a computer, you can save a sequence

of readings to a

In this article I will discuss these features

in detail and how
the meter can be accessed by your computer.

And, because no such
device is perfect, I will point out the few but

relevant flaws
you will encounter when using it.

Thank you, Susan Fowle, for writing some very

useful programs
that render the meter more user-friendly. Tom

Fowle also
deserves gratitude for his advice to a neophyte

writer on
computers such as I.

Location of Essentials--

Since this meter will not function without

its battery and fuse, it makes sense to

ascertain their
whereabouts. Orient the meter so that its

control panel faces
downward and the end containing the display

points away from you.
Notice that the bottom cover has two rubber

"feet" that extend
nearly the width of the cover. One foot is

right at the bottom
end and the other is about two-thirds of the

length distant. In
fact, it defines the beginning of the display


The door for the battery compartment -- which

accepts the 22-
182's single 9-volt battery -- comprises the

bottom end of the
cover. The Phillips screw that secures the door

is a finger's
width up from the center of the rubber foot.

In order to gain access to the fuse, remove

the four Phillips
screws that secure the meter's bottom cover.

The battery door is
actually part of this cover so you need not

remove it separately
for this operation. Two of the screws will be

found in the
extreme corners at the bottom end of the cover.

The other two
are placed at each end of the rubber foot that

defines the
beginning of the display section. When the

cover is removed, you
will find the fuse holder adjacent to the

battery and just before
the flexible protective cover for the circuitry.

All of these screws have unthreaded portions

in the middle of the
shanks which prevent their falling out of the


When removing this cover, be careful not to

jerk the wires of the

small loudspeaker which is force-fitted into a

recess in the
cover. You can remove this speaker quite easily

with your
fingers. This loudspeaker emits the various

"beeps" that
indicate the completion and status of many


The bottom cover also contains a stand that

can be extended by
grasping it from within the rectangular recess

just beyond the
battery door.

Control Panel Layout--

Orient the meter so the display points away
from you. Below the display and proceeding from

left to right
are three rectangular rubber buttons.

The first button stands by itself and is the

"power on/off"
button. Toward the right side of the panel is a

pair of similar
buttons. The first one toggles through four

states: normal
reading, data-hold, maximum, and minimum. The

button to its
right toggles between "normal" reading and

"relative" reading.
These are discussed in detail later.

Below these buttons is a large, 30-position

selector control. At
its top-left are two rectangular holes, one

above the other.
These are the holes into which the leads of a

capacitor can be
inserted for measurement. At the selector's

lower-right is a
circular object. This is a socket into which a

transistor can be
inserted for checking.

Below the capacitor socket is another

pushbutton labeled "comm."
When toggled on, the meter sends data

continuously through the
RS232 port. When toggled off, further readings

are issued only
when you press a key on your computer's


At the bottom of the panel are four holes

going from left to
right. These holes accept the connectors for

the test probes.
The probes are conventional "pencil-like"

extensions with pointed
tips. Their connections to the meter are

hollow cylindrical
plugs. The holes in the meter that accept these

plugs have a
protrusion that must engage the corresponding

center hole in the
plug. While these connections greatly reduce

the likelihood of
contact with your skin, they require frequent

attention since
they do not make connection until they hit the

bottom of the
hole. This is the first thing to check if you

get no response.

You will use the two right-most holes for

most measurements. The
farthest hole to the right is the "hot"

terminal, the one to its
left is "common." To the left of "common" are

two holes (BOTH
POSITIVE INPUT TERMINALS) for measuring current.

First comes one
for measuring up to mA200. This terminal has a

2-amp fuse. The
left-most terminal is unfused and is for

measuring up to 20
amperes. The manufacturer recommends a maximum

"on-time" for
such measurements of 30 seconds followed by

fifteen minutes rest.

The connection for the RS232 port is on the

right side of the
meter. If you feel down the side, directly to

the right of the
"hot" terminal, there is what appears to be a

"scratch" in the plastic, just above the seam.

This is actually
a row of seven small holes. The 7-pin connector

on the supplied
cable plugs into this "socket," so that the

cable extends toward
the top of the meter. The plug can be inserted

in the opposite
direction, but this will not harm the meter

since its innards are
optically isolated from the computer's serial

port. The reverse
connection of this plug results in an "I/O

error" message.

A Few Flaws--

Unfortunately, the selector knob has no

"STOP" that
would prevent continuous rotation. Although you

can determine
the setting of this control from the information

on your computer

screen, we recommend that you apply physical

markings to indicate
at least the highest ranges of voltage and

current. You will
probably want to mark other positions you use


The sockets that are used for capacitors and

transistors are
poorly designed, so you will have to use some

ingenuity in order
to ensure reliable connections between their

contacts and the
leads of the component to be measured.

Although we managed to obtain a reading for

transistor beta, it
took much "fiddling." We suggest that, since

this meter gives
you no more significant information than you can

get by checking
it with a continuity tester (see Continuity

Tester Uses, SKTF,
Fall, 1982), ignore this feature of the meter.

Meter Functions and


Turn the meter on by pressing the "power"

button. The meter will
emit a long and a short beep if it "powers up."

Pressing the
button again turns off the meter. It utters a

very short beep
when it "powers down." It turns off

automatically if no readings
are taken for about ten minutes. Be sure that

the test probes
are plugged into the two right-most sockets.

Since there is no "end stop" on the function

selector, the most
logical point of orientation is the "continuity"

Rotate the selector so that the slotted end of

its pointer is at
the "nine o'clock" position, between the two

sockets for
capacitor leads. The continuity position is

four clicks
clockwise. You can confirm that you have

selected this function
by touching the probes together and waiting for

the steady tone.
Depending on the mental gymnastics the meter's

performing, the
tone may not appear for a second or two. The

tone will not
appear if the resistance between the probes is

30 ohms or more.


The next six notches going clockwise are the
following resistance ranges: 200 ohms, 2

kilohms, 20 kilohms,
200 kilohms, 2 megohms, and 20 megohms. No

audible indication of
"overload" is presented in the resistance and

"logic low"
functions. In all other modes the meter emits a

continuous tone
when an overload condition is reached.

The display and your computer will show a

message such as, ". ol
kohm." The "PERIOD" can precede the "ol"

immediately, or
separated from it by a space, or be placed

between the two
letters. The PERIOD indicates the degree of

resolution to which
the meter is set within the function being


D.c. Voltage--

Proceeding clockwise, d.c. voltage is next.

six ranges follow in this order: 20mV, 200mV, 2

volts, 20 volts,
200 volts, and 1000 volts. Positive and

negative readings can be

A.c. Voltage--

The a.c. voltage ranges are next and proceed

reverse order: 750 volts, 200 volts, 20 volts, 2

volts, 200mV,
and 20mV. The manufacturer recommends that you

not use this
meter in circuits whose common is more than 500

volts above
"earth ground." They also pointedly discourage

the metering of
three-phase a.c. circuits with this meter. They

further state
that if, however, you insist on doing so, do

your calculations
very carefully.

A.c. and D.c. Current--

Continuing clockwise are the a.c. current,
then d.c. current ranges as follows. a.c.:

20mA, 200mA, and 2
amps. D.c.: 2 amps, 200mA, and 20mA.

For measurements up to 200mA, plug the hot

test probe into the
hole to the left of "common." For measurements

between 200mA and
twenty amperes, insert the hot test probe into

the hole at the
far left. As stated earlier -- but worth

repeating -- this jack
is not fused, and the manufacturer recommends a

maximum "on" time
of 30 seconds to be followed by 15 minutes of

"off" time.

The high-current jack is functional only when

the selector is set
to the highest current ranges. The jack for the

"hot" probe that
you use for all other measurements is rendered

ineffective in the
"current" modes.

Transistor Beta--

Then comes the position for checking

beta, designated as h, with the subscript FE.

As mentioned
previously, taking a measurement in this mode is

really more
trouble than it's worth. The socket is the

culprit. The holes
that accept the leads are too large, and there

are a lot of
them--eight, to be precise. There is a separate

semicircle of
four holes each for NPN and PNP transistors.

The manual does not
make it clear as to how to use these four holes.

It further
states that bipolar transistors, not of the

power variety, are
the only ones for which the meter is designed to

check the gain.

Logic Levels--

The next position on the selector is for
determining logic levels. The display reads

"ready" when this
mode is first selected. Connect the test probes

to the minus and
plus power supply voltages of the circuit

containing the logic
levels to be tested. Then, press the "rel"

button and start your
search with the hot probe. If the point in

question is at 70% of
the power supply's voltage or greater, the

display reads "high"
and a continuous tone is emitted. If the point

is 30% of this
voltage or less, the reading is "lo" and no

audible indication is
given. If the voltage is between these two

references, the word
"float" appears.


Clockwise from the logic mode is a

capacitance section. The progression is 2000pF,

2000nF, and
20uF. An overflow condition emits a continuous



Lastly, there is a two-range frequency meter.

first range extends to 20kHz, and the second, is

200kHz. I have
gotten a reliable reading with a signal as low

as 20 millivolts
at 1kHz. The manual advises that you not

measure a frequency
whose voltage exceeds 250 volts RMS. Here,

also, a tone is
emitted when the frequency range is exceeded.

Data Presentation Modes--

Once you have selected a function, you
have some choices as to how data is presented.

Fortunately, the
meter defaults to the conventional mode when it

"powers up." The
two buttons below the right-hand end of the

display accomplish
most of these. The left-most button toggles

through four modes:

Pressing it once initiates "data-hold"; this

causes the meter to
retain the most recent reading. Pressing it a

second time causes
the meter to display the minimum reading

observed. Pressing the
button again displays the maximum reading. The

meter updates both
maximum and minimum readings when monitoring

either parameter, so
when you change from displaying the minimum to

maximum, the latter has already been held in

memory. These data
are erased with any further change of function

or when the
meter's turned off. Pressing it the fourth time

makes it give
current readings, which is the default.

Selecting the "Relative" Function--

The right-most button toggles
between "normal" and "relative." This function

is used when
determining logic levels and in situations where

you wish to set
a numerical value as a "zero" reference, such as

a particular
voltage. For example, you may want to observe

the fluctuations
of your household a.c. voltage during peak

periods. You can
start monitoring it at 5:00 p.m., press the

"rel" button which
causes the meter to read that voltage as "0."

From there on, the
meter reads the "difference"; you can take

readings and the
display will indicate their fluctuations either

side of zero.
Pressing the button again returns the meter to


The "Comm" Function--

The rectangular button located between the
capacitor sockets and the panel that contains

the test probe
sockets toggles this function on and off. When

active, it sends
data continuously through the meter's serial

port. When
inactive, you must update the reading on your

computer with a
command from the keyboard. This function is

useful if you choose
to read the meter with your telecommunications

software. It
should not be used with either the software that

comes with the
meter or the software we have developed because

the accumulated
readings will clog the buffers quickly. These

programs can be
set to perform the same function.

Reading the Meter via your


In addition to the test probes and the cable

that connects the
meter to the serial port, the meter comes with a

3.5 inch disk
that contains three programs and a "readme.txt"

file. The
programs are: Dmm.exe, Metdemo.exe, and


The program called "dmm.exe" displays the

readings from the meter
using graphics and is not accessible. On a

computer with a
monochrome display, it merely prompts you to hit

"enter" and then
displays an "illegal function" message and

prompts you to "press
any key to return to the system."

The programs called "metdemo.exe" and

"metdemo.bas" are source
code and compiled versions of the same program.

They will send
continuously updated readings to the screen.

The ".bas" file is
written in interpreted basic such as the common

which comes with many versions of "dos". To run

such programs,
make sure that a program such as "gwbasic.exe"

is in your search
path. Then type "gwbasic" followed by the name

of the program
as, in this instance, "metdemo.bas."

In addition, Susan Fowle has created some

programs in Basic that
tailor the readings for access by speech and

Braille. These
programs are public domain, so you may share

them, but they
should not be sold. We have included them on

the disk along with
this article. A brief description of each

program follows.

In order to run programs with the .bas

extension, type "gwbasic"
followed by the name of the program and follow

the prompts.
Brtdmm.bas takes one reading with each

keystroke. The cursor
remains on the same line as the reading, making

this easy to use
with either a Braille display or a speech

program. With speech,
you will want to set a window for this line.

Focdmm.bas was designed to run with the Covox

"Speech Thing"
synthesizer, but it can be easily modified to

run with a speech
synthesizer that is driven as a DOS device,

(that is, a stand-
alone unit hooked to a serial or parallel port).

By "digital
focus" we mean that the program can be set to

present selected
portions of the reading to such a speech

synthesizer, even though
the entire reading appears on the screen.

Rptdmm.bas is also designed to work well with

a Braille display.
It continuously accesses the meter and is thus

akin to reading
the meter with the "comm" function. Pressing

any key stops the

Finally, Stdmm.bas is another program

designed to work with the
Speech Thing, but will work with other

synthesizers. It has an
option that allows each character to be spoken


Specifications for Writing your Own


The following
communication parameters are required: 1200

baud, 7 bit ASCII;
no parity; 2 stop bits.

Data Format--

Each reading consists of fourteen bytes

numbered in
the hexidecimal standard 1 through 9, and A

through E. In the
following two examples, a byte that is occupied

by a blank space
will be shown as an equals sign (for sign).

Note that byte E is
always a carriage return (


  • Example 1: dc-1.9999=v

  • Example 2:



Command Structure--

  1. The meter must receive the D command to
    activate data transmission,
  2. the computer must give the meter
    the C command to clear its memory, and
  3. the computer must give
    the meter the M command (memory call) to

    transmit data from the
    meter's memory to the software).

Cable Formats--

Since the demons of disorder dictated the
arrangement of pins in the DB9 plug so that they

bear no
discernible relationship to those in a DB25, we

present them here
in Table I. Table II shows the relationship of

the 5-pin plug
that enters the meter to the DB9 socket on the

other end of the

Table I. DB9 to DB25 pins:
  • 1-8 (Receive-Line Signal


  • 2-3 (Received Data)
  • 3-2 (Transmitted Data)
  • 4-20 (Data Terminal


  • 5-7 (Signal Ground)
  • 6-6 (Data Set Ready)
  • 7-4 (Request to Send)
  • 8-5 (Clear to Send)
  • 9-22 (Ring Detector)
Table II. 5-Pin Plug to DB9 Socket

(with the socket facing away
from you); pin 1 is in the top left corner. On

the 5-pin plug, I
will call pin 1 the pin nearest the cable.):

  • 1-2, 2-4, 3-7, 4-3, and 5-5.

As the serial port on this meter is optically

isolated from the
rest of the meter's works, the computer must

supply power on the
two handshaking lines on pins 4 and 7 of the Db9

connector. In
the provided basic programs, note the lines

which read:
OPEN "COM1:1200,N,7,2,RS,CS,DS,CD"

Those used to "dos mode" setups for serial

ports will see the
addition of settings beyond the 2 indicating 2

stop bits. These
set up the handshaking lines, 1 high and 1 low,

to provide power
for the meter's serial port. Since most

communications programs
do not allow for these settings, you may have

trouble using the
meter with such. If you need to power the meter

from another
source -- that is, you have a serial port which

can't be set up
to provide power with those handshaking lines --

a 9-volt battery
in series with a 470-ohm resistor connected with

the plus on the
meter's pin 4 and the negative on pin 7 might do

the trick.
Don't forget the resistor for current limiting

to avoid popping
the optical isolators in the meter. Failure to

provide this
voltage will result in no apparent damage, but

won't allow the
meter to see its port.



by Bill Gerrey

[At one time, I intended to call this paper

Commercially Available Folding Canes for Use by

the Blind."
However, they have steadily improved, thanks to

our involvement
in their design, so that title would be

unnecessarily snide


You would never know it from conversations

with me or by my
works, but I'm an opinionated guy. If you can

get me to talking
on a subject--and one word might do it--I have

set ideas as to
how things should be. On the subject of

available folding canes:

I hate rigidly affixed (not rubber-mounted)

tips that stick in
cracks and give you seven extra navels before

you get home. I
hate plastic tips that don't provide a good

sound source for
echoes--not making good tapping sounds--so you

needlessly walk
into trees, and you miss doorways that you are

looking for. And,
oh, I suppose, a gooey rubber handle is nice

when you're walking,
but the fact that it increases the size of the

folded instrument
by 50% makes it bust your pockets; isn't the

purpose of a folding
cane to get out of your way?

The result is, when people see my cane, they

invariably ask,
"What earthly kind is that?"



There have been various brands of these over

the years. One,
made of light aluminum, was so flimsy that it

would break under
the force of a hard rain. Others used chucks

for each section,
making a cane that was durable, but whose

collapsed length was no
more convenient than the extended instrument.

Finally, fiber-
composition canes whose sections are held

together by static
friction have become popular. (I confess to

having worked on
such a one.)

There is a friction-fit cane on the market

which is reported to
be moderately durable. Two other advantages are

that it is very
light-weight, and that it has a rubber-mounted

metal tip that
makes good sounds for echoes and which rarely

sticks in cracks.

From my experiments, I have concluded that

all friction-fit
joints have a mode of failure about which I am

duty-bound to warn

Between solids, "static friction"

("sticktion") is greater than
"dynamic friction." Users of canes held

extended by static
friction are advised to twist the ends as the

cane is pulled
taut; dynamic friction will be in play until the

operator stops
twisting, and when motion stops, it will take

more force to
dislodge the sections than was applied in

"setting" them.

This sounds just dreamy until one experiences

conditions where
sticktion is "broken" and a joint shifts

slightly. Once dynamic
friction is the only force holding the joint

together, it is
likely to collapse.

Where are those trouble spots that make your

telescoping cane go
flaccid on you? Places where vibration causes

slight movement in
a joint. What sort of terrain causes vibration?


Therefore, a friction-fit cane is most likely

to collapse in the
middle of a street--quod erat demonstrondum. As

trucks bear down
on you and you are trying to find the safety

island, you must
pull the cane taut and try again knowing that

this risk will be
no less probable a second time.

As a second spare when you're traveling,

however, you might
consider adding the NFB carbon-fiber telescoping

cane to your

Multisection Canes Held Rigid by


Various companies, Mahler, Hicor, WCIB, and

foreign-made models
exist which have four or more sections that are

pulled together
by an elastic cord when the cane is allowed to

fall from your
hand. My favorite of these is the AFB

"SuperFold." (You may
have to order this quickly, since the Foundation

itself has
spread the rumor that they are going out of

business in the area
of "aids and appliances.")

All such canes are fitted with my pet peeves:

they have rigid
tips (mostly nylon), and their bulbous handles

make you look like
you are carrying a collapsible weapon. [Bay

Area police
forcefully subdued an innocent blind bus

passenger who extended
his automatic weapon in a confident way; it sure

hit the news out

For durability, most of these models are the

same diameter over
the entire length. In my opinion, durability

requires this.
However, the resultant instrument feels much heavier than tapered
solid or telescoping canes; their center of

gravity is lower.

When I purchase folding canes (usually four

at a time), I buy a
few extra plastic tips. These can be turned on

a lathe to create
a 3/4-inch-long peg of 9/32-inch diameter. This

peg accommodates
a press-on rubber-mounted steel tip intended for

canes of the
Rain-Shine umbrella company (my favorite solid

cane, by the way).

In order to modify the handle, it is

necessary to take the cane
apart. Such canes are made in various ways, so

specifics cannot
be given here. Suffice it to say that in most

cases, the elastic
should be temporarily removed.

Taking a knife to that rubber defense device

on the top piece, I
strip down to the bare aluminum (giving that

delectable morsel to
the neighbor's dog). My choice is to replace

the rubber with
heat-shrinkable tubing; you need some insulation

there in cold

You have two choices of handle styles. One

is to fit the top end
with a "crutch tip" from the hardware store and

provide a loop an
inch or so from the top. The other is to allow

a loop of the
main cord to emerge through the top, as many

already do. The
latter arrangement is simpler, but it is not my


[By the way, the purpose of such a loop is to

hold the sections
in a bundle when the cane is collapsed. Never!, ever!, think of
this loop as a "wrist strap," as it is sometimes

advertised. If
your cane gets in a jam, such as getting trapped

under a wheel of
a vehicle backing up, you've got to be able to

disengage yourself from the cane and move to

safety. Any
suggestion that a cane has a wrist strap is


The rubber handle may have been the mechanism

for holding the top
end of the elastic cord; this is true for the

Superfold, which
uses the small hole in the end of the rubber to

trap a knot in
the cord. Often, the top section is just a

piece of tubing,
perhaps flared at its lower end to mate with the

next section.
To trap the main elastic, I borrow a trick from

the old AFB "Aluminoid Cane" as follows:

Find, or make, a washer whose diameter is a

close, but loose, fit
in the tubing. The hole in the washer should be

large enough to
accommodate the cord. Perhaps halfway down the

tube, make five
or six deep dimples around it with a center

punch. A knot in the
cord will keep it from pulling through the

washer; the dimples
will trap the washer at that point in the tube.

In order for the washer to seat properly on

the dimples, they
must be on the circumference of the precise

cross section; you
don't want the washer to cock at an angle such

that it could flip
on edge and pass through the restriction created

by the dimples.
For this reason, wrap tape around the tubing to

serve as a guide
for the center punch.

Now you can chose your loop configuration.

If the elastic has a
loop which, before, emanated from the top, you

can position the
retaining knot such that the loop still does so.

I prefer to use
smaller elastic cord to make a loop 2 inches

down from the top.

To accomplish this, I drill the diameter of

the tube at this 2-
inch distance. Eventually, I poke the two ends

of my small

elastic into the tube from either side, fish the

ends out the
top, tie the ends together in an "over-hand

knot," and pull the
loop so that the knot disappears into the tube.

(The main cord
has to have been installed first, and the shrink

tubing must also
be applied first.)

Once the top section has been dimpled and

drilled, heat-
shrinkable tubing can be installed. Most

American canes have an
outside diameter of one-half inch; the

appropriate shrink-tubing
size is 5/8- or 3/4-inch. (See "Using

Heat-Shrinkable Tubing,"
SKTF, Spring 1983.) This tubing can be gotten

in various colors;
it is my inclination to stay away from black or

gun-metal blue,
as I don't want a beating like that other blind

guy got.

The tubing should reach the bottom of this

section; however, its
position at the top depends on your style of

loop. For example,
for the arrangement where a separate loop is

positioned two
inches down, you will want bare aluminum for the

top three-
quarters of an inch so that a crutch tip can be

fitted to the
top. If your loop is intended to emerge from

the top, I
recommend the following procedure:

Thread the washer onto the cord; then feed

the cord through the
section from the top end. Determine the

position of your knot so
that the washer traps the elastic with the right

amount of loop
emerging. Making sure that the washer stays

somewhere in the
tube, pull the cord out again until the knot is

an inch or so

Cut the heat-shrinkable tubing one inch

longer than the section.
Match the bottom ends up, positioning the extra

length at the
top. Apply heat so as to shrink from the bottom

up (turning the
assembly so as to distribute the heat). When

you get to the top
with the heat source, shrink the extra length;

it will shrink
down to perhaps 5/16 inches. Then, while the

shrink tubing is
still warm and malleable, pull the cord so that

the knot folds
the shrink tubing inside the aluminum tubing.

This will produce
a finished end which won't hurt your palm when

the cane
encounters something.

Some canes may not require all of these

steps. For example, the
Superfold cane has plastic fittings at the

joints; the one in the
top section is perfectly adequate for retaining

a knot in the
cord, and all that is necessary is to position

the knot further
down. Depending on how far the modified handle

piece has moved
the position where the elastic is retained, you

may find it
necessary to shorten the cord to get the tension

back up where it

If holes in the handle have been drilled (for

installation of a
loop, for example), a tapered reamer is the best

tool for opening
the shrink tubing, although careful work with a

pointed knife
would do as well.

Earlier models of canes had few

sections--four being typical.
One of my tricks was to order five shorter

canes, use one for
parts, and make four long ones having five

sections. You can
shorten the bundled-up cane by two or three

inches that way.

Notes on the AFB


When it works, the Superfold is my favorite

folding cane (see the
first paragraph of the previous section). It

has Delrin fittings
at each joint that carry a pair of rubber

O-rings. When pressed
together, the cane does not wobble at the

joints, and it does not
rattle when in contact with rough terrain.

These O-rings make it possible to make a

6-section cane that
outperforms canes with metal-to-metal joints.

these joints are somewhat vulnerable to

breakage. Also, fittings
can come loose of the pieces they are supposed

to stay with.

Out of four Superfolds, I got three joints

(15% of them) in which
the plastic fittings had to be cemented into the

aluminum with

Right out of the package, the Superfold is

very hard to press
together and disassemble. The O-rings squeak

and refuse to seat
properly, making a wobbly assembly and causing

hemorrhages when pulling them apart. There is

an easy solution
for this, and I'm surprised it is not done at

the factory.

The same snugness of fit can be had if the

O-rings are "glazed"
with Vaseline. Generously smear each O-ring

(two per fitting)
with Vaseline; then, press the joint together

and twist it back
and forth a few times. Next, pull each joint

apart and wipe it
off with a paper towel.

Both the O-rings and the Vaseline are

petroleum products, and
they "take to each other." The glaze will

remain, even though
the fitting will not be greasy enough to soil

your pocket. (They
could glaze the batches of O-rings before they

put them on; they
would go on easier and it would save us the


On the Appropriateness of

Folding Canes

If you are a long-cane traveler, your cane is

most important for
your safety. You are more valuable than an

inanimate stick, so
if a stick must be sacrificed now and then, so

what. On the
other hand, it must be there for you when the

going gets rough.

I know people who swear by the most dainty of

canes; they say, "I
only have to replace it every once in a while,"

or, "You just
have to take care of it." Balderdash!


When I was a kid, there were product

advertisements that said,
"This makes an excellent 'theater cane.'"

Pardon my opinion
here, but a theater is full of oddly spaced

tiers, seats that can
trap your cane, people who, with a small

misstep, can render you

If you need a cane, you need a cane. Travel

styles and
situations differ, however. I travel in benign
environments--smooth, wide sidewalks--most of

the time, and I am
fairly gentle with my canes; I usually break

them when I am
abrupt with them. Some of you live in towns

with no
sidewalks--perhaps with car after car parked in

your way (the
bumpers of which eat folding canes). Still

others are heavy
handed with canes; they don't solder for a

living, so why
shouldn't they be.

When you test drive a cane, solid or hollow,

folding or not, put
thought in your confidence in it. If your cane

is too delicate,
you will travel as if you are protecting it.

Protecting your cane is dangerous. In

bailing it out of trouble,
you can side-step and fall off an edge, you can

unexpectedly back
up and be hit by a quiet bicyclist, or worst of

all, you might be
avoiding putting it where it best

belongs--taking the hits for

I need subscribers. I cannot afford to lose

you, so do me this
favor. At the slightest inkling that you might

be favoring your
cane, cast it aside and choose a mightier staff.

Products and


The AFB Superfold is available from the

American Foundation for
the Blind Product Center as the C601xx (where

"xx is replaced by
the length; my choice being the C60156). Extra

tips are No.
C61100. AFB Product Center, PO Box 7034, Dover,

DE 19903-7044;
Phone: (800) 829-0500.

The telescoping fiber cane is an NFB product.

The length in
inches follows the prefix ACG, with the suffix T

meaning it
telescopes. Thus, mine would be an ACG57T.

Order it from the
National Federation of the Blind Materials

Center, 1800 Johnson
St., Baltimore, MD 21230; Phone: (410)


My favorite tips (and canes, for that matter)

come from the
Rainshine Company, PO Box 5615, Madison, WI

53705; Phone: (608)
437-8018. Their canes are noncollapsible solid

fiberglass, and I
still have the one I got in high school. It has

survived being
tripped over and run over by trucks, as well as

being bent in a
20dg arc so as to stuff it into my gym locker

hundreds of times.