Man, PIO is so ridiculously OP.

This is just copper pads hooked up directly to gpio, and PIO state machines reading tiny changes in capacitance... without any "real" analog circuitry. (Credit to Matthias Wendel, I stole his pico-femtofarad code and made it into a 3D gesture sensing thing.)

Here's my super janky setup just to check if it would work at all

Yeah is very cool. N.B. without a licence file in the repo you have to ask him to copy his code. I want to make a room size one of those using aluminium foil sheets above the plasterboard of the ceiling, in the roof space. Cheap privacy preserving room occupancy detection etc.

I'm gonna just take it on vibes that he doesn't care if I use his code. Putting a license file in a repo containing a single 200 line micropython script would be weird.

Most likely, but given that you are both nice humans you can ask him? Whatever I do I will certainly be sharing with him.

is it just reading each pad’s capacitance and using that data to “triangulate,” for lack of a better term?

Octagulate, but yeah (plus a ridiculous amount of sensor fusion filtering to get the data to be reliable enough for that)

It really is. Why on earth would we NOT want a gaggle of extra, isolated cores for our io? Precise timing, zero jitter. It amazes me how inertia keeps the veterans from improving their game. The assembly is trivial with AI as well.

AI still kinda sucks at PIO assembly for whatever reason, but still super helpful. And yeah I've been working with ESP32s recently (someone else's decision) and omg they are such a shit show and I can't wait to go back to dealing with RP2350s.

For me, AI (claude opus) has actually one-shot everything I have asked it to do with the PIO assembly. But I have mostly asked it to port existing protocols to it.

You mean this is all Wacom and Synaptics has been doing the whole time?!

Yeah, and your phone.

What are the limits of this in terms of the size the pads (so capacitance) and detection range? Would it work if instead of those pads you used... a house roof made of metal sheets to detect overflying airplanes? (I mean at low altitude close to the airport or sth, not at FL400)

idk, but that would be sick. I kinda live in the perfect place to test that. I'm like a couple miles away from a little private airport directly on the approach line.

Is this open source? I'd like to build something on top of this!

Yep, here you go:

Amazing! Done right, PIO is an absurdly powerful tool.

interesting! how did you go frame raw capacitance outputs, to proximity on a grid? Was there a sort of calibration step?

The arrangement is kinda hardcoded into a 4x2 grid. But yeah there's a "no hand" calibration at boot and then it uses a bunch of sensor fusion stuff to continuously calibrate out drift and noise. Mostly just a ton of hand tuning until it matched.

very cool! that sounds like where the magic is. i wonder if it could be combined some computer vision 🤔

Yeah I'm a big fan of combining a bunch of different kinds of sensor data to make it feel super rock solid. I was considering an array of magnetometers too. Just cap sense alone is soo noisy

Is the Apple trackpad built on similar principles? It looks awesome!! Just add a small motor and you can build a fully haptic trackpad!!

I see how it tracks across cells but inside….? What is that magic

Just a fuckton of math, and remembering that digital is just an abstraction layer on top of analog. What it’s doing is pulling a pad high, then switching it to an input and waiting until it reads low, doing it ungodly fast to measure capacitance. Then more math to get a position

But how do you know where you are on the pad ? I would have assumed that there would be some amount of symmetry for capacitance and that you wouldn’t be able to detect where you are with respect to the center but apparently no…?

You get the readings from the ones next to it, it doesn’t even really treat treat any one pad in a special way, it’s just always taking the centroid of all 8 pads.

That’s nuts.

Thanks, yeah I'm surprised this works too

amazing!!

Thanks! Maybe I should make this an HID controller and use it with your joypad thing

YES!!! It’s a perfect. I’m just adding more and more USB/BT output modes. New web config about to push live.

Oh sick. I'll check it out

Ping me anytime or jump in the discord. Project is very Claude code friendly. Can practically make custom controller firmware anything platform with just prompts.

Great, looks like you can build a button matrix out of it as well. What you could try next is salvage a tft panel with a faulty driver board and without the panel cracked which has a circuit matrix and try turning it into a touch panel. Could be some tech they could have used to make them touch screen in parallel to operating as polarizing filters.