• 1
    setup sensor and led

    from machine import ADC
    from machine import Pin
    import time
    adc0=ADC(0)                    
    led=Pin(4,Pin.OUT)
    target=200
    while True:
      print("gas=",adc0.read())    
      time.sleep(1) 
      if adc0.read() > target:
        led.value(1)          
      else:
        led.value(0) 

  • 2
    wiring

    -MQ135

    A0 = A0

    GND = GND

    VCC = 5V

    -LED

    +  = D2

    -  = GND