来自：https://forum.micropython.org/viewtopic.php?t=9839&p=55065#p55065

PRP2040上的ADC输入通道比较少，下面的方法可以为提供更多的ADC通道，每个通道需要2个引脚，2个电阻和2个电容。

两个电容的电荷由通过输入电阻R2和反馈电阻R1的电流平衡。PIO尝试将输入引脚上的电压保持在其低/高阈值之间。如果使用合适的输入电阻，则可以测量更高和更低的电压。

title= "pioAdcB" # by CWE
# Adc sigma delta type
 
from machine import Pin
from rp2 import PIO, StateMachine, asm_pio
from time import sleep
 
maxTime=1_000_000
 
@asm_pio(sideset_init=PIO.OUT_LOW)
def cap_prog():
    mov(y, osr) # OSR must be preloaded with max
    mov(x, osr)  
 
    label("test_pin") # 
    jmp(pin, "is_set") 
    jmp(y_dec, "not_set") # just count it 1
    label("not_set")
    #nop() .side(1)
    jmp(x_dec,"test_pin") .side(1) # 2
    jmp("save_result")
 
    label("is_set")
    # nop() .side(0)
    nop() # 1
    jmp(x_dec,"test_pin") .side(0) #2
 
    label("save_result")
    mov(isr, y) #.side(0) # save result; pin low
    push(noblock)
 
 
 
 
class PIOCAP:
    def __init__(self, sm_id, outPin, inPin, max_count, count_freq):
        self._sm = StateMachine(sm_id, cap_prog, freq=2 * count_freq, sideset_base=Pin(outPin), jmp_pin=Pin(inPin,Pin.IN))
        # Use exec() to load max count into ISR
        self._sm.put(max_count)
        self._sm.exec("pull()")
        #self._sm.exec("mov(isr, osr)")
        self._sm.active(1)
        self._max_count = max_count
 
    def getCap(self):
        #self._sm.exec("push()")
        return self._sm.get()
 
cap = PIOCAP(0, 22, 17, max_count=(maxTime), count_freq=50_000_000)
 
mittel=0
while True:
    onTime= maxTime-cap.getCap()
    mittel=(9*mittel+onTime)/10
    #print(onTime, mittel, (onTime/maxTime))
    print(onTime, 7.309-1.4369e-5*onTime)
    sleep(0.1)

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