WAT

A PMS7003 particle dust sensor hooked to some hacky code to make Geiger noises, and stuffed into a scavenged meter to make it look like proper test-gear.

WHY?

My vague theory was that while you could generate graphs and heatmaps of pollution, and have people nod along with your explanation and go ‘Dear me yes that’s terrible something must be done..’, if you really wanted to put the fear of imminent death into them, you needed it to make noises generally connected to imminent death.

Hence a Geiger counter.

HOW?

As is almost traditional, I was sitting and listening while the adults around me discussed how to do sensible electronics projects with sensible objectives and well-considered code. I think someone wanted to build a dust sensor into a hat. I probably opined that it would be an interesting experiment to have a rig like that make Geiger counter noises, and to see how onlookers felt about that. I also probably got told to go and build my own if I was so clever.

And there the matter rested until a few of us happened upon a skip filled with NASA technical reports, bits of broken university, and abandoned testgear. Among which was the temperature sensor pictured.

There are times when the universe pretty much erects a sign in front of your nose, which features a big arrow and the words ‘This way’. This was one of those times.

I spent the next yea-long wondering how I could write sensible code that called Earle Philhower’s excellent ESP audio library from some interrupt so I could construct a semi-random stream of pulses, with the duty-cycle dependant on the values coming from the dust sensor, and some hysteresis built in because you can only sensibly get new numbers from the thing every ten seconds or so.

In the end I just used a random number generator and let the Arduino void loop {} do the donkey work. It’s rubbish and probably eats batteries.

DID IT WORK?

Ho fuck yes it did. Mind, it works best on Gen X because we grew up with that sort of thing.

C0de, of a sort: https://bitbucket.org/hirez/geiger/src/master/