March 1960 Popular Electronics
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That John T. Frye was a great short story writer is a given
truism based on his decades-long production of the Carl &
Jerry series in Popular Electronics. It is easy to look over
the fact that he also had artistic skills as well as evidenced
by the pencil drawings that accompanied each installment. In
this episode, our two electronics hobbyists build a resistor
anemometer to measure wind speed from within their basement
workshop. In the usually storyline style, one boy gives a lesson
in circuit design while the other (also the reader) is the attentive
Carl & Jerry: A Hot Idea
By John T Frye
The buffeting March wind spanked Carl with the slamming basement
door as he stepped into the electronic laboratory of his friend,
Jerry: The latter was sitting with his head encased in a pair
of muff-type earphones connected to an amplifier with a variable
frequency audio oscillator working into its input. As Carl looked
at his chum aimlessly adjusting the frequency of the oscillator
and the gain of the amplifier, he decided there was something
about Jerry's appearance that was not right. There was a certain
lackluster look about his eyes, and his round face looked fatter
than ever - but in a sort of lopsided way.
"Guess I'm the one guy in ten for whom it won't work," Jerry
said with a lugubrious sigh as he shut off the equipment and
removed the earphones.
"What won't work, and what's the matter with your face? It
looks twice as big as it ought to."
"The 'audio anesthetic' won't work for me. I've got an infected
wisdom tooth that's killing me, and I have an appointment with
the dentist in an hour. But the other day I read that a Boston
dentist discovered that music or random noise put into earphones
worn by a patient killed the pain of dental work in 90% of 2000
cases tested. The patient adjusts the sound level with a gain
control in his lap until the sound blocks out the pain sensation.
A company in Rochester is already in production on the device.
I was trying to see if I could kill the pain of my toothache
with various frequencies from the audio generator, but I couldn't."
"That thing must work on a variation of the 'mule skinner'
principle," Carl said. "You know a veteran mule skinner always
took the ear of a mean mule between his teeth and bit down hard
while he was putting on the bridle. The idea was that while
the mule was thinking about how much his ear hurt he couldn't
think about kicking or biting the mule skinner. With the audio
anesthetic, while the mind is concentrating on the sound it
ignores the pain. Your trouble is that in fooling around with
ham radio, etc., you've trained yourself to be a little smarter
than the mule. You can listen and still be thinking about your
aching tooth at the same time. Well, I better scram and let
you go to the dentist."
"Oh, no, you don't!" Jerry exclaimed.
"I've a little chore for you to perform while I'm gone; and
I just know you wouldn't refuse your poor, pain-wracked buddy."
"Depends on what my poor, pain-wracked, scheming buddy has
"All I want you to do is mount this thermistor anemometer
out on the garage and run this cable from it back into the lab."
"You know," Carl said thoughtfully, "I don't think you've
got a toothache at all. You've just dislocated your jaw on one
of those big words you're so fond of. What the heck is a 'Mistermometer'?"
"I said a 'thermistor anemometer.' As you know, or should
know, an anemometer is a device for, measuring wind velocity.
This one is intended to do so by the use of thermistors. A 'thermistor'
is a resistor whose resistance changes, in a nonlinear fashion,
incidentally, with a change in temperature. The temperature
affecting the resistance may arise externally or it may come
from current flowing through the thermistor. In the case of
these thermistors you see on the bench, an increase from -60
to plus 150 degrees centigrade will cause the resistance to
fall from about 2000 ohms to one ohm."
"That sounds dandy for measuring temperature, but I don't
see how they can be used to measure wind velocity."
"Keep listening and you will."
"I've arranged two matched thermistors and two resistors
- one variable - in a bridge circuit," Jerry explained as he
sketched the familiar diamond-shaped bridge circuit. "These
two top legs are the thermistors; the two bottom legs are the
resistors. Here's a battery in series with a switch connected
between the common junction of the two thermistors up here and
the common junction of the two resistors at the bottom. A d.c.
meter connects from this left-hand thermistor-resistor junction
across to the right-hand thermistor-resistor junction.
"Now, when the variable resistor is properly adjusted to equal
the fixed resistor, the battery current divides equally between
the left and right sides of the bridge. Since the same current
flows through each thermistor, any resistance change in one
is duplicated by the resistance change in the other, and the
bridge stays in balance. Voltage drop along the two sides is
identical, and no current flows through the meter."
"How do you know the thermistors in your bridge are matched?"
"Because I matched 'em. I put the bridge in the freezer where
the temperature is below zero and then put it in that light-bulb-heated
oven and brought the temperature up to 150 degrees. I kept repeating
this test with different combinations of thermistors until I
found two that would go through the temperature swing with practically
no indication of current through the meter at any point. You
"Yep, but how does the thing measure wind velocity?"
"As you can see, one thermistor is mounted inside this aluminum
can with tiny holes in the top and bottom to permit outside
air to filter very slowly through. The other thermistor is mounted
out in the open so wind can blow around it freely. When battery
current flows through both thermistors, heating them, the heat
is lost to the surrounding air. In a dead calm, the heat lost
by the enclosed thermistor and the heat lost by the one outside
in absolutely still air will be the same and no reading will
show on the meter.
"However, when a wind is blowing, the heat from the exposed
thermistor will be carried away; the harder the wind blows,
the faster heat is lost. Heat lost by the enclosed thermistor
in its artificial calm will remain the same. The wind-cooled
thermistor will stay high in resistance while its hotter buddy
inside the can will go lower in resistance,. unbalancing the
bridge and permitting current to flow through the meter. All
we have to do is to calibrate this current-indicating meter
in terms of wind miles per hour and we have a remote-indicating
anemometer with no moving parts."
"I suppose. this little wooden umbrella-shaped canopy is
to keep the sun and rain from influencing the reading."
"Right. Actually the whole thing is pretty crude, but I want
to put it up for a while and see how much rain and sun does
affect it. This variable March weather is ideal for making such
a study. Will you put it up?"
"Oh, I reckon," Carl said gruffly. "Quit stalling and get
to the doctor."
Actually Carl was as eager as his friend to tryout the new
gadget, and he lost no time after Jerry had gone. It took but
a few moments to fasten the device securely to the garage gable
and to run the four-wire TV antenna rotor cable back into the
basement through a casement window. There he connected two of
the wires to the battery-and-switch combination, and the other
two were connected to the milliammeter. When the switch was
thrown, the meter indicated up-scale; and Carl was fascinated
by the way the meter reading kept step with the roar of the
March wind outside. He was still watching the meter when Jerry
came in the door.
"You're still kind of fat in the face," Carl remarked critically,
"but you look better. Could he save the tooth?"
"He can if he wants to; I left it with him," Jerry replied
breezily. "He yanked it out, and it didn't hurt a bit."
"Just wait until that dope starts dying out," Carl said with
the voice of experience. "Your gadget is working fine, Jer.
Watch how the meter pointer moves up every time the wind bends
the tops of those trees through the window there - hey, that's
funny," he broke off. "It was working swell, but look at the
crazy way it's behaving now."
The meter was acting strangely. No longer did the pointer
keep step with the roar of the wind. First it bobbed up and
down the scale erratically and then began backing off scale
below zero. Finally it settled firmly against the left-hand
stop and refused to budge until Carl opened the switch; then
it came to rest on zero.
"Something's gone wrong out there. You stay here and watch
the meter while I go have a look," Carl suggested.
He had hardly reached the top of the outside basement stairs
when he began shouting; "Call the fire department! Call the
fire department! Kreuger's barn across the alley is on fire,
and is it ever going!"
Jerry rushed upstairs and called the fire department, and
then he ran out in the back yard. By this time the old two-story
frame barn across the alley was a mass of flames; and blazing
shingles were sailing all around. Long tongues of flame reached
across and licked at Jerry's garage.
The fire department came roaring up and started playing water
on the burning barn and the other buildings nearby, but the
fire was not put under control until it had burned the high
tension wires overhead in two.
"Boys, that was close," the fire chief said to Carl and Jerry.
"If the thing had had ten minutes more start with this wind,
that whole row of garages could easily have gone. It certainly
is a good thing you spotted it when you did. How did you happen
to see it?"
"Well, we were kind of tipped off by a sort of fire detector
we had installed on our garage roof," Jerry explained lamely.
He knew from bitter experience the difficulty of trying to describe
the working of electronic equipment to people without an electronic
"Actually it's not hard to figure what happened," he said
to Carl after the chief had gone and the two boys were walking
back to their laboratory. "The wind was blowing right from the
fire toward our garage. When a tongue of flame would lick over
and slu-u-urp that exposed thermistor, the can would protect
the enclosed thermistor from the quick increase in temperature.
As a result, the exposed thermistor got hotter than the enclosed
one, and this made the meter read backward."
Jer, old buddy," Carl said as he laid an affectionate arm
across his friend's shoulders, "the thing I like about you as
an inventor is that you always invent something. Of course,
you may set out to invent a thermistor anemometer and end up
with a jim-dandy fire detector; but, by golly, you come up with
something! Man, you're the most!"
"Thanks, pal - I think!" Jerry answered as he grinned crookedly
up with his still swollen face at his friend.
Carl & Jerry: Their Complete Adventures is now available. "From 1954 through 1964,
Popular Electronics published 119 adventures of Carl and Jerry, two teen boys with a passion for electronics and a knack
for getting into and out of trouble with haywire lashups built in Jerry's basement. Better still, the boys explained how
it all worked, and in doing so, launched countless young people into careers in science and technology. Now, for the first
time ever, the full run of Carl and Jerry yarns by John T. Frye are available again, in five authorized anthologies that
include the full text and all illustrations."
Carl & Jerry Episodes on RF Cafe
- Carl & Jerry: Anchors Aweigh, July 1956
- Bosco Has His Day, August 1956
- The Hand of Selene, November 1960
- Feedback, May 1956
- Abetting or Not?, October 1956
- Electronic Beach Buggy, September
- Extra Sensory Perception, December
- Trapped in a Chimney, January 1956
- Command Performance, November 1958
- Extracurricular Education, July
- Treachery of Judas, July 1961
- The Sucker, May 1963
- Stereotaped New Year, January 1963
- The Snow Machine, December 1960
- Extracurricular Education, July
- Slow Motion for Quick Action,
- Sonar Sleuthing, August 1963
- TV Antennas, August 1955
- Succoring a Soroban, March 1963
- "All's Fair --", September 1963
- Operation Worm Warming, May 1961
- The Crazy Clock Caper, October 1960
- Two Detectors, February 1955
- Tussle with a Tachometer, July 1960
- Therry and the Pirates, April 1961
- The Sparkling Light, May 1962
- Pure Research Rewarded, June 1962
- A Hot Idea, March 1960
- The Hot Dog Case, December 1954
- A New Company is Launched, October 1956
- Under the Mistletoe, December 1958
- Electronic Eraser, August 1962
- Blubber Banisher, July 1959
- "BBI", May 1959
- Ultrasonic Sound Waves, July 1955
- The River Sniffer, July 1962
- Ham Radio, April 1955
- El Torero Electronico, April 1960
- Wired Wireless, January 1962
- Electronic Shadow, September 1957
- Elementary Induction, June 1963
- He Went That-a-Way, March1959
- Electronic Detective, February 1958
- Aiding an Instinct, December 1962
Posted May 29, 2014