Closing a Circuit with a PIR Sensor

I am trying to build a rudimentary camera trap using a PIR senso. The camera itself is triggered by a circuit closing, so I need to find a way for the circuit to be open, and then when the PIR sensor detects motion, have it close, then reopen afterwards. I believe I read that the best way to do this is with a relay, but I am not sure which kind to use, if there is any difference between them.

Thank you for any help in advance!

Yes, a relay could do it, or a transistor. Relay has advantage of isolation. Exactly which relay to use depends on the voltage you have available and the output of the PIR sensor. So I’ll ask some questions;

  • what is the power supply voltage you will use to power the PIR sensor?
  • what current can the power supply provide?
  • what current does the PIR sensor use?
  • what is the make and model of the PIR sensor?
  • what is the output of the PIR sensor?

Speculating; a PIR sensor is often a commercial or retail assembly powered at 12V with a relay built into it, using normally closed (NC) contacts, so that if an alarm cable is cut the alarm triggers. If that’s the case here, another method can be to open the PIR sensor assembly and wire up to the unconnected normally open (NO) contacts of the existing relay. Or it could be a semiconductor output, in which case the above is void.

Edit: relay also has disadvantage of contact failure if very low current is drawn by the camera shutter trigger circuit; I’ve heard this became a problem if the device was placed in a remote location unsupervised for a long time, and the researcher came back to find animal tracks but no photographs. :grin: