The 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.
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.
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 together, since they are made at the same time and under the same conditions. In other words, they match very well. I used that feature to build a novel oscillator, which turned out to be extremely stable.”
Within a year, other manufacturers were copying the design. “Everybody was stealing from everybody else,” Hans recalled, “and in those days, nobody paid any attention to patents.” In fact Signetics didn’t even apply for a patent, fearing that if they tried to enforce it, they would start a war with other, larger companies. Today, anyone can build a copy of a 555 timer.
The 555 established Hans Camenzind as an authority on analog integrated circuits. By 2006, he had designed 140 standard and custom chips. He also wrote two amazing books: The definitive Designing Analog Chips, and a brilliant general introduction to electricity titled Much Ado About Almost Nothing, which included thumbnail biographies of all the pioneers. Both books are still available online through print-on-demand.
The 555, of course, has acquired legendary status. You can even buy a kit to build your own macro-scale replica from discrete components.
The chip has some well-documented defects. Its use of bipolar transistors results in a nasty voltage spike when its output transitions (see Figure C), and it is power-hungry. But a CMOS version has fixed those issues.
Hans Camenzind died in 2012 at the age of 78. Today, the storefront where he designed the timer is occupied by a real-estate broker (see Figure D). The alley is arrowed in the picture of Murphy Avenue in Figure E. Maybe one day Sunnyvale will honor Hans with a plaque beside his old workplace, but in the meantime his genius lives on in tens of billions of chips containing copies of his hand-made circuit.
The writer thanks the Camenzind family for their generous help, and Jack Ward of the Transistor Museum, where audio files of Hans Camenzind are archived here
Eric Schlaepfer has a lifelong passion for vintage electronics — especially cathode-ray tubes, which he has repurposed as functional art objects such as clocks. He speaks lyrically about “the joy of a vectored display, with glowing phosphors.”
But his most widely known project is a macro-scale 555 chip. “I found an old datasheet which showed the components, even including the resistor values,” he says. “I built a copy from transistors and resistors, and it worked.” (The circuit is shown in Figure F.)
Eric’s big 555 is a handsome piece, shown in Figure G. Naturally, he showed it to people — including Lenore Edman and Windell Oskay, cofounders of Evil Mad Scientist Laboratories, which sells maker products. Windell has his own fetish for old electronics, such as Nixie tubes, so he and Lenore came to the obvious conclusion: They could sell Eric’s big 555 as a kit.
The assembled version is shown in Figure H, and it’s for sale here. If you have steady hands and good eyesight, there’s also a surface-mount version.
Eventually, Windell hopes to market a macro-scale 6502 microprocessor containing 3,510 transistors, if he can resolve some frustrating component supply issues. In the meantime, he has built a CNC-cut, laser-engraved, wooden (nonelectronic) 555 footstool, shown in Figure I with optional cat.