After almost frying my Pi with my last question, I thought I'd better ask if what I have seemingly working is ok and won't cause me any problems.

I have a modern wireless doorbell that I am powering from the pi by using the 3.3v pin to the positive on the chime and the negative of the chime to a ground pin on the Pi. So far so good?

Then to sense when the doorbell has been activated I'm taking an input from the positive side of an LED that lights when the doorbell is ringing to pin 25 of the Pi. That seems to register around 2v.

It consistently recognises when the doorbell is activated, and so seems to be ok, but I just wanted to check I wasn't doing anything that would harm the Pi or catch fire!

Many thanks for any assistance. Once again, apologies for any incorrect terminology.


  • 1
    You really need to check how much the chime draws. I hope you are not providing the power via a GPIO. You say 3V3 pin, so pin 1? It would be better to power from the 5V rail if that would not screw up the voltage of the output LED or the chime. The input side to monitor the LED sounds fine. – joan Oct 2 '15 at 7:55
  • Thanks for the response. Yes, pin 1. The doorbell takes two 1.5v batteries, so I assumed the 3.3v pin would be best? Is there a reason the 5v would be better? Thanks once again. D. – Darren Oct 3 '15 at 9:33
  • 1
    The 5V line has more power (in milliamaps) available, basically all the 5V you are feeding into the Pi less the amount used by the Pi and peripherals. The 3V3 line has a smaller regulator and so you can only draw of the order of 100 mA total. But as your system works that is not really a concern. As you say the use of 2 x 1.5V batteries suggest it needs 3V. – joan Oct 3 '15 at 9:42

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