from machine import Pin

enc = Pin (27, Pin.IN,)
snt = Pin (13, Pin.IN)

ev = False
pulso = 0
MAX_VOL = const(20)

def conta(p)
    global ev, pulso

    pulso = pulso + 1 if snt() else pulso - 1
    if pulso % 2 == 0:
        ev = True

enc.irq (trigger=Pin.IRQ_FALLING,
        handler=conta)

while True:
    if ev:
        if pulso < 0:
            pulso = 0
        elif pulso > MAX_VOL:
            pulso = MAX_VOL
        print (f"Volume {pulso//2}")
        ev = False