Homage to a
Handmade Chip
T
he most enduringly successful chip in
electronics history was created by one
man working in a back-alley storefront.
His name was Hans Camenzind, the chip was
the 555 timer, and this year marks its 50th
anniversary. It has outlasted all competitors, is
still being manufactured in basically the same
design, and has sold billions worldwide.
The 555 has endured because it is amazingly
versatile and reliable. It can time an interval
ranging from a millisecond to an hour — or
can generate a pulse stream at a frequency
exceeding 1MHz. It can create audio tones, and
can even function as a logic gate. I consider
it so important, despite its age, I devoted two
chapters to it and several experiments in my
book Make: Electronics.
Inside the Apple II, the blink rate of the cursor
was controlled by a 555. It has set the delay of
intermittent car windshield wipers, and has
been used in spacecraft. In fact the SE555-SP
variant, still available from Texas Instruments,
is space-rated. The everyday version in Figure
A
currently retails for 50 cents apiece, while on
AliExpress, generic 555s are 10 for $1.
Origins
In the late 1960s, Camenzind was wondering how
to put an AM radio receiver on a chip. Normally a
receiver uses inductors to discriminate between
broadcast frequencies, but inductance is difficult
to build into an integrated circuit.
He thought that someone, somewhere must
have made a tuned circuit that didn’t require an
inductor, so he spent several days searching the
MIT library in Boston, where he finally found the
answer: A 1935 article describing an almost-
forgotten concept called a phase-locked loop.
This could generate such a precise frequency,
he realized it could be used for something more
interesting than a radio. It would be ideal for an
oscillator, or a timer.
He took his idea with him when he relocated
with his wife and children to the Bay Area to
join Signetics, an upstart company that was
trying to compete with Fairchild Semiconductor,
the industry leader. But after two years, Hans
became impatient with their “stodgy” attitude. He
accepted a salary cut, became an independent
consultant, rented his storefront, and set out to
pursue his dream.
He built benches and shelves with boards from
a lumber store, and since his wife, Pia, was an
accountant, she did the bookkeeping. “He had a
stipend of $1,200 per month from Signetics,” Pia
recalls. “We cut our expenses to the minimum.
We never went out to dinner. But I thought — he
needs to do this.”
Hans was 36, had four children, and $400 in
the bank. Later, he described his decision as
“reckless.” Still, he came up with a circuit, and
breadboarded it using everyday transistors and
resistors. He then tested it using equipment
loaned by Signetics, and tried endless iterations,
varying the component values because he
wanted it to work even when the manufacturing
process introduced errors.
Having perfected the circuit, he started on the
most arduous part. Chip production requires
multiple photographic masks when layers of
silicon are partially etched away. In 1971, the only
way to make the masks was by cutting them into
plastic film known as rubylith, using an X-Acto
knife at a scale of maybe 400:1.
Even at Intel, the vastly more complex 4004
(the first true microprocessor) was fabricated
from hand-cut masks, because computer-aided
design didn't yet exist. Hans spent many days
hunched over a light table, cutting plastic and
removing areas with tweezers.
The Launch
When Hans delivered his masks to Signetics, he
faced a new problem: Engineers at the company
were skeptical that anyone needed a timer
chip. Fortunately, the marketing manager, Art
Fury, overruled the engineers. It was Fury who
assigned the easily-memorized 555 part number.
A micrograph of the very first Signetics 555
wafer is shown in Figure
B
on the following
page. The chip was an immediate success,
because it worked so well. You got consistent
results if you ran it from a 5V supply or 18V. It
worked the same way when driving a 20mA LED
or sourcing 200mA for a small motor.
“Integrated components have the disadvantage
of being inaccurate,” Hans wrote later. But,
“Whatever their variation may be, they all vary
19
make.co
Charles Platt, courtesy Pia Camenzind
M82_018-21_555timer_F1.indd 19M82_018-21_555timer_F1.indd 19 7/11/22 12:37 PM7/11/22 12:37 PM
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