[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.

This solar tracker system uses the Arduino ... the LDR are connected as INPUTs and position the servo motor at 90° then wait for a 2 seconds before the code execution inside the loop(). In the loop() ...

Here is the diagram of my Arduino infrared close proximity sensor. As you can see, the core part of my experimental setup is an Arduino UNO, but other compatible microcontrollers can also be employed.

you can just build it a custom sensor with an Arduino Uno. This paper shredder bin monitor is an easy Arduino project for beginners to get into. It uses an ultrasonic sensor, which is placed ...