touch: add capacitive touch sensing on normal GPIO pins #709
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Tested on the following chips/boards: * RP2040 (Raspberry Pi Pico) * ATSAMD21 (Adafruit PyBadge) * NRF52840 (PCA10056 developer board) * ESP8266 (NodeMCU) * ATmega328p (Arduino Uno) * ESP32C3 (WaveShare ESP-C3-32S-Kit) * FE310 (SiFive HiFive1 rev B) The sensitivity threshold in the example may need to be adjusted per board though, the default value of 100 typically recognizes when a cable is being touched but the RP2040 for example is capable of doing much more precise measurements if the power supply is sufficiently noise-free.
aykevl
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This PR is basically a better version of https://github.com/tinygo-org/drivers/tree/release/makeybutton which I am certainly willing to deprecate. |
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Oh I didn't realize we already had a capacitive touch driver! |
I like that a lot better for sure.
Not that big a feature missing, plus I dislike the name I gave that feature anyhow. Let's merge and mark the other as deprecated? |
Sure, sounds good :) |
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Now merging, thanks for the addition @aykevl |
It is possible to make a capacitive touch button out of any GPIO pin on most MCUs. The input may be somewhat unreliable compared to dedicated hardware, but it probably works well enough for most people. The way to do this is by connecting the GPIO pin to ground through a 1MΩ resistor, charging the pin by setting it high, switching to input, and measuring how long it takes to discharge (through the 1MΩ resistor).
Most of this is handled inside the driver. All you need to do to make this work is to connect an 1 mega-ohm resistor to the GPIO pin and to ground, and to connect some sort of metal surface to the GPIO pin. To avoid ESD issues, it's probably best to cover the metal surface with a thin non-conducting layer (Scotch tape for example).
Tested on the following chips/boards:
There are loads more I could test, but with this list I'm fairly confident it's going to work on nearly any MCU that's running at a high enough clock rate.
The sensitivity threshold in the example may need to be adjusted per board though, the default value of 100 typically recognizes when a cable is being touched but the RP2040 for example is capable of doing much more precise measurements if the power supply is sufficiently noise-free (it can even detect a finger at ~1cm with a large enough pad!)
This capacitive touch driver does detect the amount of noise on the input and tries to adjust for it, but the algorithm can probably be improved still. I'm not all that familiar with DSP algorithms. I might make a PR in the future to improve this if I get around to it.