So I have a fairly simple doorbell system. It has an AC transformer that supplies about 12.5VAC to the doorbell circuit. One of the 12.5V wires between the transformer and the chimes is interrupted by a an illuminated pushbutton.
The button has an incandescent light in parallel with a switch. This light allows some voltage through to the chimes at all times - about 0.25VAC at the chime terminals. When you push the button, the full 12.5VAC is sent to the chimes causing the ring.
My dilema is trying to find a simple way to sense the pressing of that button. I have easy access to the transformer but I can't think of anything I can do there except have a current transformer ring around one of the wires to sense the power burst. It would be a lot harder to do something at the doorbell or chime end (drywall work).
Is there any clever trick I can implement near the transformer that will allow me t sense the press with a GPIO pin?