The Aiphone uses a m50761 Microcontroller which runs at 5v
The Sonoff I'm using uses the PSF-B85 (esp8265) which is 3.3v
I have located the transistor on the intercom circuit board that connects to the microcontroller doorbell detect pin.
This pin is 0v normally and goes to 5v when the doorbell is pressed
I'm using GPIO5 on the ESP module and want that to detect as a "Button Press" when the doorbell is pressed.
I know I can't put 5V into the ESP module or the magic smoke will escape.
From what I can see at the moment GPIO5 is usually 3.3v and detects a "button press" when it's shorted to ground.
What is the best way to interface this 0v / 5v signal to the esp to read as a button press?
Would a simple resistor to reduce the 5v to 3v work? or do I need a little more circuitry?
Disclaimer: I have a little electronics knowledge but not a lot, and I'm learning as I go.