So I've got some code that looks like this:

import pifacedigitalio as p
import time

while True:
    p.digital_write(0, 1)
    p.digital_write(1, 0)

As the input changes, the indicator LED switches on and off. As it does, it makes an audible clicking sound. Doesn't seem right to me! What could be causing this?

  • 2
    When you say indicator led, is it pi's internal led's or external led's that you have connected for the project? Thanks
    – giri-sh
    Dec 29, 2015 at 8:19
  • Output pins 0 and 1 :) Cheers!
    – Koobz
    Dec 29, 2015 at 8:32

1 Answer 1


The PiFace includes a relay (2 actually) the clicking sound you hear is the relay (the small black boxes) activating and deactivating. Inside the relay is a small metal arm that moves to make electrical contact. The clicking is normal. This video explains how a relay works.

  • 1
    You don't really want to switch mecahnical relays too often. They have a limited number of cycles. 5 times a second might not be too bad.
    – joan
    Dec 29, 2015 at 9:18
  • Yeah - My car has a relay without any contacts (a solenoid?) just to make a tick-tick noise when I use the indicators (turn-signals) as the flasher unit is electronic and totally silent and the Car manufacture thought that a sound was needed for those.
    – SlySven
    Dec 30, 2015 at 2:47

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