The amount of light reaching the LDR from the LED decreases as the pipe is bent, and with a simple divider circuit a voltage can be read by an Arduino.

The sensor shown here is essentially two plates mounted side-by-side, attached to an Arduino Nano using the Capacitor library which uses just two pins, one digital and one analog.

Use Arduino to handle sensor input and relay control. Pi runs a Python Flask server with a simple UI to toggle GPIO pins via serial commands sent to the Arduino. Use cron jobs on Linux to schedule ...