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Comment by progbits | Hacker News Reader

This is mechanical bouncing.

Real environments have both mechanical bouncing and unavoidable EMI spikes, even when you have done your best to eliminate EMI; particularly when you're dealing with switches, which are typically on the end of long wires which are effectively antennae. Source: actual experience with crappy real-world systems.

A side-note: I have a friend who is an electronics genius who managed to construct a production system that combined a multi-kilowatt electric arc lamp and a CCD array. Microvolts of CCD signal at megahertz of bandwidth mixed with hundreds of watts of RFI all in the same chassis. Oh, and of course lots of low-jitter digital timing and sequencing electronics and wideband ADCs.

It all worked perfectly. He used every trick in the book, and some new ones he invented from scratch, to implement it - I've never seen anything like it, before or since.

Sounds fascinating, can you share what it was for?

Regarding your parent message, I agree, but the EMI stuff will depend on lots of other factors and so you will have to do your own modeling / measurements. While the mechanical bouncing should be pretty uniform so this is a nice data source for picking a well behaved switch and designing debouncing network.

Of course I'm just realizing this is N=1 for the switch so hard to say what manufacturing tolerances each one has.

That's overly broad. I do embedded development, where the unit has a metal box and the button is plastic. You'd have to deliberately hit it with a spark generator to cause an unexpected transition, and having the button register an unexpected transition isn't a big deal. Worse would be to have overly-enthusiastic debouncing that slows down the user interface, making the unit annoying to use.

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