October 1962 Popular Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
magnetic switches were a relatively recent invention that came out of Bell Labs
when this Carl & Jerry episode was published in Popular Electronics
magazine in 1962. It seems like such simple and common components have been around
forever, and they have for a growing portion of people in the electronics realm
since that was more than half a century ago. As is often the case with John Frye's
enterprising pair of teenage experimenters, the reader is treated to a tutorial
on the operational theory of the switch, with its dependence on magnetization by
induction. The story ends up being quite humorous, and reminds me a bit of the old
All in the Family episode where a window salesman uses a
photography light measuring meter to convince Archie he is actually detecting severe
air drafts around the windows, when in fact it is merely registering a greater light
level near a window.
Carl & Jerry: The Difference Detector
A Carl and Jerry Adventure
By John T. Frye W9EGV
Jerry was hunched over a bench in the lab and workshop of WCCR, the master control
station of the Parvoo University campus wired wireless system. Since he and Carl
had helped Jimmy Young, the station manager, run down a "wildcat" broadcast station
the previous semester, the two boys had been privileged to work and experiment in
the shop. Jerry grinned to himself as he heard heavy feet pound the stairs outside;
and a minute later his chum, Carl, came puffing through the door.
"Hey! What are you trying to do ... shake me?" Carl demanded.
"No, I left a note on the tack board in our room telling you where I was going;
but, as usual, you obviously never thought to look at it. Come on over here. I've
something to show you."
"It doesn't look like much," a still unmollified Carl sniffed, glancing down
at a couple of skinny little glass capsules on the bench. Each was about 3/4" long
and 5/32" in diameter. A stiff piece of shiny wire protruded some 3/8" from either
end of the capsule.
"I intend to make you eat those words," Jerry warned. "These are 'bi-reed magnetic
switches,' first developed by Bell Telephone Laboratories and now manufactured by
several different companies. If you will look closely, you will see that each nickel-iron
wire is flattened out into a blade just after it passes through the end-seal into
the capsule, and that these blades extend past each other for a short distance and
are separated by a few thousandths of an inch. What you can't see is that the opposing
surfaces of the overlapping portions of the blades are coated with diffused precious
metal - probably gold - to form contacts, and that the inside of the glass envelope
is filled with a mixture of nitrogen and hydrogen."
"Very fascinating, I'm sure," Carl remarked as he made an elaborate pretense
of smothering a yawn.
Instead of answering, Jerry connected a flashlight bulb, a battery, and one of
the bi-reed switches in series. Next he held a little rod of black metal about an
inch long and a quarter of an inch in diameter parallel to the glass capsule and
about an inch away from it. The bulb lighted. He pulled the metal rod back a half
inch, and the bulb went out.
"What's that little black stick?" Carl demanded, becoming interested in spite
"Its a small alnico magnet. When I hold it close to the switch, the two blades
are magnetized by induction with opposite polarity and attract each other into contact,
lighting the bulb. When I remove the magnet, the spring of the blades pulls them
apart and restores them to their original position."
Jerry held the magnet about a half-inch from the glass-enclosed switch so that
the bulb was lit; then he carefully slid a small plate of soft iron between the
switch and the magnet. The lamp went dark. He removed the plate and the light came
"That soft iron plate 'shields' or 'short-circuits' the magnetic field, however
you want to think about it," Jerry explained, "and allows the switch to open. I'm
told that one auto manufacturer is using, or intends to use, devices like these
as limit switches on his electrically operated windows. Current to a directional
winding of an operating motor passes through a bi-reed switch held closed by a nearby
magnet. When the window reaches the end of its travel, a small soft-iron vane attached
to the window frame slides between the magnet and the switch, causing the latter
to open and cut off power to the 'up' or 'down' winding of the motor, as the case
may be. Neat, huh ?"
"Very neat," Carl agreed. "You could use the same system in reverse as a burglar
alarm on a house window by letting the vane slide out of the way and close the switch,
sounding an alarm, when the window was raised. I hereby retract my slighting remarks
about your little jewels."
"Oh, there's more," Jerry insisted as he reached over and picked up a little
hollow solenoid 7/8" long and 3/8" in diameter. The magnetic switch was disconnected,
slid into the hole in the center of the coil, and restored to its battery-and-bulb
circuit. Leads from the coil winding were connected through a milliammeter to a
variable-voltage d.c. power supply. As Jerry slowly turned the knob to increase
current through the coil, the flashlight bulb snapped on when the current reached
4 ma. When it was reduced to 2.5 ma., the lamp went out.
"As you've already guessed," Jerry said, "magnetism for closing the contacts
is now being furnished by the small current flowing through the thousands of turns
of that 2000-ohm coil. Our bi-reed switch has thus been converted to a sensitive,
high-resistance relay that can, for instance, be used in the plate circuit of a
tube. Not all switches I've tried are as sensitive as this one, but none take more
than a few milliamperes of coil current to close them."
"But that's only a single-pole relay," Carl pointed out.
"Yes, but it's a simple matter to elongate the opening in the coil so that several
bi-reed switches can be slid in side by side to form a multi-contact relay," Jerry
answered. "And you can work another slick dodge to achieve a normally closed set
of contacts. You simply slide a little magnet in alongside a switch to keep the
contacts closed. Then the direction of current through the coil is arranged so its
magnetic field bucks and cancels that of the permanent magnet, thus allowing the
contacts to open when the coil is energized."
"Somebody did a lot of thinking about and playing with those switches," Carl
"You're right; and no wonder: they're small and light; their firm contact pressure
makes them ideal for use in dry circuits; their hermetically sealed contacts can
be used in explosive atmospheres without danger; and the small contact spacing makes
them very fast, with less than a millisecond actuation time."
"How about power-handling ability?" "I've no specifications on these tiny switches,
but I doubt they're designed to handle much power. I'd say a tenth of an ampere
or so would be all you'd want to apply to the contacts. Bi-reed switches are made
in various sizes, though, and a slightly larger model is advertised as being able
to handle 15 watts into a resistive load, with currents up to 1 ampere and voltages
up to 250 volts."
At this moment Jimmy Young stuck his head into the door of the shop. "Say, you
two. I'm supposed to go over to the Women's X Hall tomorrow night and check out
the operation of the new slave station we've just installed there. Would you foxes
like to accompany me to this chicken roost ?"
"Yes!" Carl and Jerry said in chorus. "I'll be handling the transistorized field
strength meter; one of you can make like he's monitoring with a little receiver;
but I don't know what the other's excuse for tagging along can be," Jimmy reflected.
"He ought to be carrying something."
"Don't worry," Carl said hastily. "I'll have something to carry. Just wait and
And when they met in front of the girls' residence hall the next evening, Carl
was carrying something. It was a little cube of mahogany, about 2" on an edge, with
a red-tinted flashlight bulb sticking out the top. Burned into the other five faces
were crude reproductions of the symbols for Male, Female, Birth, Death, and Infinity,
copied straight from the beginning of the Ben Casey TV program. Jimmy eyed this
suspiciously, but before he had a chance to quiz Carl about it they were ushered
into the house, preceded by a warning cry of "Man in the house!" and a great scurrying
up and down stairs.
Jimmy set about checking the signal strength. His indicator was actually a small
meter connected in the collector circuit of one of the agc-controlled i.f. stages
of a transistorized receiver. As he went from room to room, the meter deflection
gave an indication of the relative strength of the wired wireless signal. Jerry
had an earphone in his ear and listened for any interference to the program with
another little receiver. Carl brought up the rear with the mysterious little mahogany
cube balanced on the palm of his outstretched hand. The little red bulb was dark,
but Carl kept his eyes glued to it as though expecting something dramatic to happen
Nothing did happen, though, until they moved into the lounge where several girls
were sitting around chatting and watching TV. As Carl's blue eyes swept the scene,
they settled on one rather plain-looking girl off in a corner by herself looking
wistfully through her horn-rimmed glasses at the others. Quietly Carl edged around
the room until he was standing beside the girl; then he gave a startled exclamation
as the little red bulb flashed brightly. "Here's one!" he called excitedly to Jerry.
Conversation halted abruptly in the room as everyone stared at Carl and the glowing
red bulb. It continued to burn brightly until he took three or four steps backward,
and then suddenly it went out. A step forward toward the startled-looking girl in
the glasses brought it back on.
"Wha-what is that?" she quavered. "It's a difference detector," Carl answered
"My friend and I stumbled on this physio-electronic phenomenon a short time back,"
Jerry explained glibly. "While we don't understand it completely ourselves, we know
the device reacts strongly to the difference of the sexes - if you'll pardon the
expression. When in the hands of a strong masculine type, such as my friend Carl,
the little red bulb glows brightly in the presence of a strongly feminine type.
What it reacts to is a combination of attractiveness, charm, sex appeal, what our
parents called 'It - in short, all the qualities that make a girl a girl. Maybe
I can show you what I mean. Carl, back away until the light just goes out."
Carl did, and Jerry reached over and gently removed the girl's glasses, revealing
a pair of lovely violet-colored eyes. Instantly the red light flashed on.
"See how the simple act of removing the glasses enhanced the feminine charm of
this girl and increased the intensity of her difference field?" Jerry asked.
"I-I've been thinking of getting contact lenses," the girl said shyly.
By this time all the girls in the room were clustered around Carl. One took the
little block of wood from his hand, and instantly the light went out. The block
was passed from hand to hand, turned every which way, shaken violently, and even
pounded savagely with a spiked high heel; but the light refused to come on until
the difference detector was returned to Carl's hand and he moved to the side of
the girl who was still holding her glasses in her hand.
"I hate to break up this charming little seance," Jimmy said sarcastically, "but
I promised the house mother we'd clear out of here by ten and it's already seven
minutes past; so if you girls will kindly tear yourselves away from my assistants,
we'll be going."
The last thing the boys saw as they went out the door was all the girls clustered
around the one Carl had spotlighted with the difference detector.
"All right, you strong masculine type, how did you do it?" Jimmy demanded.
"It's really quite simple," Carl answered with a chuckle as he juggled the little
block of wood back and forth in his hands. "The bulb is connected through a bi-reed
switch to a little flashlight battery. The switch is mounted in a shallow groove
right in the bottom of the block and is concealed by a thin layer of veneer glued
over it. Tucked through the inside of my signet ring is this powerful little magnet,
no larger than a pencil lead and painted flesh color.
"When the bi-reed switch was aligned with the magnet and close to it," he continued,
"the lamp lighted. I could make the lamp go on or off by moving the block very slightly
in my hand. Those symbols were burned on the outside just to hoke it up and fit
in with the story Jerry and I concocted."
"Well, you certainly gave one girl a large evening, and you also shook up some
of the hoity-toity campus queens back there in the lounge," Jimmy reflected; "but
the next time I have an invite to a women's residence hall, remind me to leave you
two scene-stealers behind, will you?"
Posted March 10, 2022
(updated from original post on 6/8/2015)
Carl Anderson and Jerry Bishop were two teenage boys whose
love of electronics, Ham radio, and all things technical afforded them ample opportunities
to satisfy their own curiosities, assist law enforcement and neighbors with solving
problems, and impressing – and sometimes toying with - friends based on their proclivity
for serious undertakings as well as fun.
Electrical Shock - September 1955
- A Low Blow - March 1961
- The Black
Beast - May 1960
Electronik, September 1958
- Pi in
the Sky and Big Twist, February 1964
Bell Bull Session, December 1961
Boogie, August 1958
- TV Picture,
Eraser, August 1962
Trap, March 1956
at Work, June 1956
Aweigh, July 1956
Has His Day, August 1956
- The Hand
of Selene, November 1960
or Not?, October 1956
Electronic Beach Buggy, September 1956
Extra Sensory Perception, December 1956
in a Chimney, January 1956
Performance, November 1958
of Judas, July 1961
- The Sucker,
New Year, January 1963
Snow Machine, December 1960
Extracurricular Education, July 1963
Slow Motion for Quick Action, April 1963
Sleuthing, August 1963
- TV Antennas,
a Soroban, March 1963
Fair --", September 1963
Worm Warming, May 1961
Operation Startled Starling - January 1955
Light Subject - November 1954
Teaches Boy - February 1959
- Too Lucky
- August 1961
and Jeopardy - December 1963
Santa's Little Helpers - December 1955
Tough Customers - June 1960
Pocket Radio, TV Receivers
Yagi Antennas, May 1955
Stomping, March 1962
- The Blubber
Banisher, July 1959
- The Sparkling
Light, May 1962
Research Rewarded, June 1962
- A Hot Idea, March
- The Hot Dog
Case, December 1954
New Company is Launched, October 1956
the Mistletoe, December 1958
Eraser, August 1962
- "BBI", May 1959
Sound Waves, July 1955
- The River
Sniffer, July 1962
- Ham Radio,
Torero Electronico, April 1960
Wireless, January 1962
Electronic Shadow, September 1957
Induction, June 1963
- He Went
Detective, February 1958
an Instinct, December 1962
- Two Detectors,
with a Tachometer, July 1960
and the Pirates, April 1961
The Crazy Clock Caper, October 1960
Carl & Jerry: Their Complete Adventures is
now available. "From 1954 through 1964, Popular Electronics published 119 adventures
of Carl Anderson and Jerry Bishop, two teen boys with a passion for electronics
and a knack for getting into and out of trouble with haywire lash-ups 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."