I am humbled to see the extent of invention on these forums, and I can't even achieve a simple ambition. I'd be very grateful for help.
I have a keyfob transmitter and receiver. The rx is linked up to my Arduino, where it is used to switch on another device. Instead of the tx being triggered using the push-button as normal, I want it to be triggered by a miniature PIR sensor. Can anyone suggest how I might do this? The push-button is reasonably accessible for soldering in the centre of its board.
Assuming your push button connects a pin to ground when pushed:
Most PIRs have an open collector output. Wire that to the same pin the button is connected to. Then either the push button or the PIR can take the pin low & trigger the TX.
I was in a fog previously, hung up on the idea that the NO push button was connecting two conductors when pushed, whereas the PIR was sending a momentary voltage signal. But that seems really logical and simple now you say it. Thanks so much!