from machine import Pin, Timer

led = Pin(17, Pin.OUT)
tim = Timer()
N = 0
def tick(timer):
    global led
    global N
    if(N>0):
        N = N - 1
        led.toggle()
    else:
        led.off()

# 100Hz for 10 seconds
N = 40
tim.init(freq=20, mode=Timer.PERIODIC, callback=tick)