Capacitive Touch Sensing using Pico / RP2040 PIO using similar API to CircuitPython's "touchio"

touchpio.py

# touchpio.py -- Capacitive Touch Sensing using Pico / RP2040 PIO using similar API to CircuitPython's "touchio"
# 24 Feb 2023 - @todbot / Tod Kurt
# # Uses ideas from "# PIO Capsense experiment / -scottiebabe 2022" from
# https://community.element14.com/products/raspberry-pi/f/forum/51242/want-to-create-a-capacitance-proximity-touch-sensor-with-a-rp2040-pico-board-using-pio/198662
#
import time, array
import board
import rp2pio
import adafruit_pioasm
from supervisor import ticks_ms

class touchpio:
    capsense_pio_code = adafruit_pioasm.assemble(
    """
    pull block           ; trigger a reading, get maxcount value from fifo, OSR contains maxcount
    set pindirs, 1       ; set GPIO as output
    set pins, 1          ; drive pin HIGH to charge capacitance

    set x,24             ; wait time for pin charge
charge:                  ; wait (24+1)*31 = 1085 cycles = 8.6us
    jmp x--, charge [31]

    mov x, osr           ; load maxcount value (10_000 usually)
    set pindirs, 0       ; set GPIO as input

timing:
    jmp x--, test        ; decrement x until timeout
    jmp done             ; we've timed out, so leave
test:
    jmp pin, timing      ; loop while pin is still high

done:
    mov isr, x           ; load ISR with count value in x
    push                 ; push ISR into RX fifo

    """)

    def __init__(self, touch_pin, max_count=10_000):
        self.max_count = max_count
        self.pio = rp2pio.StateMachine( touchpio.capsense_pio_code,
                                        frequency=125_000_000,
                                        first_set_pin = touch_pin,
                                        jmp_pin = touch_pin )
        self.max_count = 10_000
        self.buf_send = array.array("L", [max_count] )   # 32-bit value
        self.buf_recv = array.array("L", [0] )  # 32-bit value
        self.base_val = self.raw_read()
        print("base_val:",self.base_val)
        if self.base_val == 0xffffffff:  # -1
            raise ValueError("No pulldown on pin; 1Mohm recommended")

    def raw_read(self):
        self.pio.write( self.buf_send )
        self.pio.readinto( self.buf_recv )
        return self.buf_recv[0]  # return 32-bit number from PIO

    @property
    def raw_value(self):
        return self.max_count - self.raw_read()

import touchio  # to compare against

touch_pins = ( board.GP8, board.GP9, board.GP10, board.GP11 )
touchs = [touchpio(p) for p in touch_pins]         # try with touchpio
#touchs = [touchio.TouchIn(p) for p in touch_pins]  # try with touchio
vals = [0] * len(touchs)

while True:
    t = ticks_ms()
    for i in range(len(touchs)):
        vals[i] = touchs[i].raw_value
    dt = ticks_ms() - t

    print("\n",dt, end=' ')
    for v in vals:
        print(v, end='  ')
    time.sleep(0.05)

# touch1 = touchpio( board.GP10 )
# while True:
#    t = ticks_ms()
#    val = touch1.raw_read()
#    dt = (ticks_ms() - t)
#    dval = (touch1.base_val-val)
#    print(dt, hex(val), dval, "*" * int(dval/30) )
#    time.sleep(0.05)
    
    
    
# NOTE:
    # this is too slow (1msec per pin)
    # def read_pin(self, apin):
    #     apio = rp2pio.StateMachine( touchpio.capsense_pio_code,
    #                                 frequency=125_000_000,
    #                                 first_set_pin = apin,
    #                                 jmp_pin = apin )
    #     apio.write( self.buf_send )
    #     apio.readinto( self.buf_recv )
    #     apio.deinit()
    #     return self.buf_recv[0]  # return 32-bit number from PIO

For more fully-developed version of this idea, see: https://github.com/todbot/picotouch/tree/main/circuitpython/picotouch_grid/picotouch_grid