ESP8266 Community Forum

Just a simple sensor you can build yourself.
Examples on my weblog with an PNP and a NPN transistor, a resistor and a capacitor.
Very sensitive and easy to build, for just a few dollars. Maybe you even have the electronics already in stock.

Can be attached to an ESP8266 or ESP32 for remote surveillance of your washing machine, water tank, aquarium, plant soil monitor etc. etc. etc.

Prototype (on breadboard), schematics and build instructions on my weblog:
http://lucstechblog.blogspot.com/2021/1 ... level.html



Have fun
Luc

This type of sensor is useful.

However, I think you want to ensure there is a defined emitter load resistance otherwise the Iceo leakage current has nowhere to go and could be a seen as a high with a high impedance input like a raw GPIO. I would ensure there is always an emitter load resistance less than say 100K.

In your example you connected to D8 (GPIO15) which does have a 10K resistor to ground providing a path for the leakage current so that's OK but other GPIOs don't have a built in load or even worse have a pull up resistor.