May 1962 Popular Electronics
[Table of Contents]People old and young enjoy waxing nostalgic
about and learning some of the history of early electronics. Popular Electronics was published from October 1954 through
April 1985. All copyrights (if any) are hereby acknowledged.
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.
See all articles from
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
"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
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 glowed brightly.
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 the center.
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 on d.c."
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
"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
"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
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
"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 still dark.
"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
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
"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 story.
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 other cars.
"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!"
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
|- Electronic Beach Buggy
- September 1956
- Extra Sensory Perception
- December 1956
- Trapped in a Chimney
- January 1956
- Command Performance
- November 1958
Education, July 1963
- Treachery of Judas,
- 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
- 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
Hot Idea, March 1960
- The Hot Dog
Case, December 1954
- A New Company
is Launched, October 1956
the Mistletoe, December 1958
Eraser, August 1962
- Blubber Banisher,
- "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
August 5, 2014