This tutorial assumes that you have some basic electronics experience, can experiment with Arduino, and have some basic ... Here, a standard light-dependent resistor (LDR) is used as an analog input ...

[Gord Payne] has one with an elegant sensor ... 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.

You can even build yourself something simple based on an Arduino Uno! The build uses Panasonic’s cheap “Grid-EYE” infrared array as the thermal sensor, in this case, a model with an 8×8 ...