The Basics of the 555 Timer IC

The 555 timer is undoubtedly one of the most important and ubiquitous integrated chips in history. It has also been over 40 years since the introduction of the 555, and no major changes have been introduced, making it one of the longest running designs in history as well.

555
The Texas Instruments NE555P Timer IC.

The 555 was originally designed in 1971 by Hans Camenzind, a Swiss electronics engineer employed by Signetics in California. Camenzind spent months working on the final design, building several different test iterations by hand on a breadboard with discrete components. When the design was finalized, Camenzind sat at a drafting table and used a razor to cut the circuit design into a sheet of plastic. In total 23 BJTs, 15 resistors, and 2 diodes were cut into the plastic. This was then reduced to produce the etching mask for etching onto the silicon wafers. That kind of beginning-to-end design work by one man is now done by large teams of engineers with complex design, simulation, routing, and etching software to handle the difficult task of modern IC design.

The 555 is ridiculously simple to use, dead reliable in an extremely wide array of applications, and remarkably robust in what it can handle and do. And in all of it’s applications, everything comes down to one of it’s three main operation modes: monostable (or “one-shot”), astable (or oscillator), and bistable (or flip-flop). EVERY circuit out there that uses a 555, and there are countless iterations, comes down to one of these three modes.

With just a couple hours of time and some basic electronics know how, it’s easy to see how versatile the 555 timer can be. Commercially it’s used in everything from toys to spacecraft, and hobbyists are still finding new ways to implement it. Check out my Instructable for more on the basics of how the internals of the 555 work.

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