May 1962 Popular Electronics
Table of Contents
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In this adventure, Carl and Jerry use a pair of General Electric
pnpn junction photoelectric switches to exact revenge on an
engineering student 'friend' at Parvoo U. It involves embarrassing
the guy in the presence of his YL (Hamese for young lady) date.
The switches, per Jerry's tutelage, work like a silicon-controlled
rectifier (SCR), except light is used to trigger the conduction
path rather than an electrical gate signal. The devices are
"solid-state kissing cousins of vacuum tube thyratrons." That's
not necessarily the way I would have put it, but OK. You are
also treated to a discussion of how and why to tame a chattering
relay with a diode rather than a big capacitor. Author and creator
John T. Frye ceased writing the stories before the two boys
graduated from college, so we'll never know what became of them.
Carl & Jerry: The Sparking Light
A Carl and Jerry Adventure
By John T. Frye W9EGV
"Hey, Jer," Carl called as he came swinging through the door
of the Parvoo University residence hall room he shared with
his hometown pal, Jerry Bishop, "guess what I just heard down
He stopped in mid-sentence at the sight of the intriguing
array of equipment spread out on the desk in front of Jerry.
This included a VTVM, a bell transformer, some pilot-light bulbs,
a multi-cell flashlight with the lens removed and two wires
leading from an adapter screwed into the bulb socket, plus several
tiny objects that looked like elongated clear glass beads with
gold-colored wires protruding from opposite ends.
"What are you up to behind my back ?" Carl demanded accusingly.
"Not a thing, but while you were shooting the breeze up and
down the halls I've been experimenting with these developmental
General Electric subminiature silicon pnpn light-activated switches,"
Jerry retorted. "Two of them are Type ZJ235A; the other two,
Type ZJ235B. I conned a lab Prof into the loan of them."
"What are they? Come to think of it, where are they?"
"Right here," Jerry replied, poking the little glass beads,
each of which was about three tenths of an inch long and one
eighth inch in diameter, with a forefinger. "You know how a
silicon controlled rectifier works. In spite of voltage applied
across it, it passes no appreciable current in either direction
until a signal voltage is applied to the gate lead; then it
conducts heavily in the forward direction like an ordinary silicon
rectifier, even after the signal voltage is removed from the
gate. When the applied voltage is removed, the rectifier lapses
again into its non-conducting state. These switches work the
same way except that light, instead of a gate signal voltage,
triggers them into conduction. Both devices are solid-state
kissing cousins of vacuum tube thyratrons.
"Let me show you," Jerry offered.
"See: I have a pilot lamp and a ZJ235A connected in series
across the secondary of this bell transformer whose primary
is plugged into the a.c. line. Watch what happens when I shine
this penlight on the little rectifier."
When the cone of light struck the semiconductor, the lamp
bulb glowed at about half its normal brilliance. When the penlight
was shut off, the light bulb went out.
"Current flows through the bulb only during the half of the
a.c. cycle being rectified," Jerry explained. "Remember, this
'switch' passes current only in one direction even when 'closed'
by the presence of light. Now I'll parallel the ZJ235A with
another unit that's reversed so it will pass the other half
of the cycle during the presence of light."
He did so and demonstrated that when the light beam shone
on either switch, the lamp glowed dully as before; but when
the beam covered both silicon units simultaneously, the lamp
The VTVM, with the meter pointer adjusted to rest at center
scale with no applied voltage, was then connected across the
lamp. Rectified d.c. voltage across the bulb made the pointer
swing right or left according to which switch was illuminated;
but when both switches were receiving the light, the a.c. voltage
present across the bulb left the meter pointer quivering in
One of the light-activated switches was removed, and a relay
was substituted for the bulb. Now light shining on the switch
would cause the relay contacts to close; however, the relay
hummed and chattered until Jerry connected an ordinary silicon
diode across the relay coil. This quieted the relay completely.
"That diode is connected so that its polarity presents a
very high reverse resistance to the d.c. pulses delivered by
the semiconductor switch," Jerry continued; "but it has a very
low forward resistance to the e.m.f. produced by the collapsing
field of the armature coil between pulses. The result is that
current flows through the relay coil at all times. During the
pulse, current flows from the power supply through the coil.
Between pulses, self-induced current of the coil flows through
the diode. The continuous current gives the relay no opportunity
"Wouldn't a big capacitor connected across the coil accomplish
the same thing by feeding stored current through the coil between
pulses?" Carl wanted to know.
"Yes, but that arrangement has two drawbacks. First, the
presence of the capacitor would slow down the pull-in and drop-out
time of the relay. Second, the light-activated switch would
be working into a capacitive load instead of the resistive or
inductive loads for which it is rated. The d.c. voltage stored
in the capacitor would appear in series with the a.c. voltage
applied and would substantially reduce the r.m.s. voltage that
can safely be applied to the switch without exceeding peak voltage
ratings. But let's see how the educated speck of silicon acts
Jerry connected one of the ZJ235A's in series with a lamp
bulb across the leads coming from the batteries in the big flashlight.
When the flashlight switch was closed, nothing happened; but
when the penlight beam struck the semiconductor switch, the
bulb glowed brightly. Its light continued undiminished after
the penlight was shut off. But when the switch on the flashlight
was opened, the bulb went out and refused to light again even
when this switch was closed until light from the penlight once
more "closed" the pnpn switch.
"On d.c. that thing acts like a latching relay," Carl observed.
"Once it starts conducting, you have to remove the power to
make it stop. How much light is required to trip it?"
"Between 80 and 500 foot-candles, with 125 foot-candles being
a typical value. And in some applications the ZJ235D, which
is rated at 400 peak volts, will handle 160 watts. Unlike ordinary
photocells, it needs no amplifiers to control considerable power.
For example, it can operate heavy-duty relays directly. At the
same time, its tiny size permits it to be mounted behind a small
hole in a meter face so that the shadow of the pointer
cutting off light shining onto the unit through that hole could
operate it. Since the input is light, the input and output circuits
are entirely separate from each other ...
"What were you going to say before we got started on all
this?" Jerry finally asked.
"Oh, I was going to tell you that Jodi, the nice YL kid from
Florida we met when we were tunnel-stomping a couple of months
ago, has a date tonight with that big ox, Bruce, down the hall.
How he talked her into it I'll never know, unless he used some
of that hypnotism of his. Anyway, he was telling a gang in his
room how he plans to park with her at The Wall tonight under
the pretext of showing her an imaginary satellite about which
he is supposed to have some inside info. It makes my blood boil
to think of him using a cheap trick like that on our - I mean
Jodi. Anyway, we still owe him one for making you look silly
with that post-hypnotic-suggestion bit."
"Yes-s-s-s-s, that we do," Jerry said thoughtfully as he
rolled one of the little light-activated switches between a
thumb and forefinger; "and this may be the time to pay off.
Doesn't he have classes all afternoon?"
"Yes, but what have you got in mind?"
"Come down to the parking lot for a look at his car and I'll
show you. Just let me collect a few things first."
The Wall was a Parvoo tradition. It was a secluded area at
the edge of the campus alongside a retaining wall where couples
were permitted to park unmolested by the university police.
School officials apparently felt it was better to have the students
park where they would be safe than invite robbery and attack
by parking on back roads.
The parking lot was just across the street from the H-3 Residence
Hall. Bruce's car was not locked, and Jerry quickly set to work.
First he disconnected the battery. Then he removed the wire
going from the fuse block to the door-operated switches for
the dome light of the car. A wire was run from the hot side
of the fuse block through one of the light-activated switches
and directly to the dome light bulb. The threads of the screw-on
glass cover of the dome light were coated with Duco cement and
the cover was screwed into place.
The light-activated switch was mounted in a small cardboard
tube so that the light gathered by a small lens in the end of
the tube focused on the light-sensitive silicon area. The tube
was mounted underneath the car at the rear with the lens pointing
backward. A little paper cap was sipped over the lens, and the
battery was reconnected. Now, opening the doors did not cause
the dome light to come on, but removing the cap from the end
of the cardboard tube did. Naturally, one the switch was triggered
"closed" by the daylight, there was no way to turn the dome
light off except to disconnect the battery. Pulling the bypassed
dome light fuse or working the bypassed dome light switch had
no effect whatever.
The battery was disconnected again while the lens cap was
replaced. One end of a short length of string was cemented to
the lens cap and the other end was cemented to the concrete
beneath the car. Finally, the battery cable was replaced.
"When the sun sets," Jerry explained, "there won't be enough
incident light to trigger the switch, even with the aid of the
light-gathering lens. It will be almost dark when Bruce drives
off for his date; so the automatic removal of the lens cap at
that time will not trigger the switch."
"Won't he think it funny that the dome light doesn't come
on when he opens the doors ?"
"He'll just think the bulb burned out and won't bother to
replace it. After all, light in that car is not exactly what
he wants tonight!"
Carl and Jerry never waited more impatiently for the start
of a date of their own than they waited to see Bruce waddle
out to his car about eight o'clock. Both heaved a sigh of relief
as he drove away from the parking stall with the dome light
"So far so good," Carl remarked. "According to Bruce's announced
plan, he intends to drive around for a couple of hours while
he exposes Jodi to 'the full force of his winning personality'
and sells her on the satellite story. That means he should be
parking at The Wall about 10:00. What say we study for an hour
or so and then amble over that way?"
This they did, but judging from the frequent glances at their
watches. it's doubtful either of them got much out of the studying.
At 9:30 they took the powerful flashlight and strolled over
to the field across the road from The Wall.
It was a beautiful warm spring night, and the boys lay on
their backs on the grass and studied the stars sparkling overhead.
They became so engrossed in identifying the great rectangle
of departing Orion, the sickle of Leo, and the parallel lines
of Gemini, that they were astonished to see it was 10:30 when
a car drove slowly down the road and joined several others parked
at widely separated points along The Wall.
"That's Bruce's car," Carl muttered as the tail-lamps flickered
out. "It was thoughtful of him to park so that the rear of the
car is aimed our way. How close do we have to be to trigger
the switch with this flashlight?"
"Well, the flashlight puts a lot of candlepower into a very
small spot, and the lens in front of the ZJ235A increases the
effectiveness of the light many times, but let's Indian-crawl
a little closer to be sure. See if you can hit the lens with
the first beam of light."
When they were within fifty yards of the car, Carl took careful
aim with the long barrel of the flashlight and pushed the switch.
Instantly the interior of the car was bathed with light from
the dome lamp. Jodi could be seen peering expectantly up through
the windshield at the silhouette of the water tower on the hill
in front of the car. She obviously had bought the satellite
Bruce's fat hand reached up and worked the dome light switch,
casually at first and then vigorously, with growing exasperation.
He opened his door and punched the little push-button switch
on the door jamb repeatedly. Then he heaved himself out of the
car and went around to the door on Jodi's side and did the same
thing, but the light kept right on burning. By this time his
plight had attracted the amused attention of couples in the
"That your sparking light, Bruce?" a voice called.
"Smart girl, that one," a feminine voice observed. "She knows
better than to be alone with you in the dark."
"Drop dead, you jokers," Bruce snarled from where he lay
on his back beneath the steering column reaching up for the
fuses mounted on the rear of the firewall. But pulling the dome
light fuse had no effect. Carl and Jerry could hardly restrain
their laughter as they watched him wrenching vainly at the cemented
dome light cover.
"Hey, Bruce, your little see-the-satellite scheme isn't doing
so good, is it?" a voice drawled from the darkness.
That did it. Carl and Jerry could see Jodi talking fast and
angrily. Then they watched Bruce switch on the headlights, back
out into the road, and drive away with the interior of the car
still brightly lighted.
Wanting to see the finale of their efforts, Carl and Jerry
took a short cut to X-Hall where Jodi lived and concealed themselves
in some shadows near the door. Almost immediately Bruce's car
came down the street, and it had scarcely stopped rolling when
Jodi popped out of her door and slammed it hard behind her.
"All I've got to say to you," she said indignantly in her
rich Southern accent, "is that I've never been so embarrassed
in my whole life. Don't ever ask me to go out with you again.
And if I were you, I'd change schools. An EE who can't turn
off a little old lamp bulb is going to make a pretty sorry engineer!"
"Wow! That's telling him!" Jerry chuckled as Bruce slammed
the car into gear and drove away with an angry screeching of
tires. "Steamed as he is, he undoubtedly will disconnect the
battery tonight and plan on looking the car over good tomorrow;
so as soon as he leaves the car, we'll remove the ZJ235A, wash
off the Duco with a little acetone, and restore the wiring to
its original condition. Tomorrow, when he finds everything working
normally, he'll think he's flipping his wig. And I'll bet Jodi
will really appreciate our looking out for her when we tell
her about it."
Carl gave his pal a quizzical look.
"Jer," he said slowly, "nobody makes better sense when he
talks about electronics than you do; but this one time you'd
better listen to me. Let's not say a thing to Jodi about this.
If there's one thing a girl can't stand, it's having someone
think she isn't capable of handling the curliest wolf that ever
trotted down the path. If she learned we were protecting her
without being asked, she'd be as mad at us as she is at Bruce."
Jerry's round face puckered into a thoughtful frown in the
moonlight and then smoothed out into a cheerful grin. "Could
well be you're right," he acknowledged, "but suppose on the
way back to the parking lot you tell me where you learn these
interesting things about how girls think!"
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 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
- Electronic Eraser,
- Electronic Trap, March
- Geniuses at Work, June
- Eeeeelectricity!, November
- Anchors Aweigh, July
- Bosco Has His Day,
- The Hand of Selene,
- Feedback, May 1956
- Abetting or Not?, October
- Electronic Beach
Buggy, September 1956
- Extra Sensory
Perception, December 1956
- Trapped in a Chimney,
- Command Performance,
Education, July 1963
- Treachery of Judas, July
- The Sucker, May 1963
- Stereotaped New
Year, January 1963
- The Snow Machine, December
Education, July 1963
- Slow Motion for
Quick Action, April 1963
- Sonar Sleuthing, August
- TV Antennas, August 1955
- Succoring a Soroban,
- "All's Fair --", September
- Operation Worm Warming,
- The Blubber Banisher,
- The Sparkling Light, May
- Pure Research Rewarded,
- A Hot Idea, March 1960
- The Hot Dog Case, December
- A New Company is Launched,
- Under the Mistletoe,
- Electronic Eraser,
- "BBI", May 1959
- Ultrasonic Sound Waves,
- The River Sniffer, July
- Ham Radio, April 1955
- El Torero Electronico,
- Wired Wireless, January
- Electronic Shadow,
- Elementary Induction,
- He Went That-a-Way,
- Electronic Detective,
- Aiding an Instinct,
- Two Detectors, February
- Tussle with a Tachometer,
- Therry and the Pirates,
- The Crazy Clock Caper,
Posted August 5, 2014