This build is inexpensive, effective, and a great way to learn basic sensing with an analog input. In some systems, a simple LED or laser diode is used to create a light source to provide illumination, however, even with initial calibration the light source will degrade with time. If it is desirable to. A photoresistor (also known as a light-dependent resistor, LDR, or photo-conductive cell) is a passive component that decreases in resistance as a result of increasing illuminance (light) on its sensitive surface, in other words, it exhibits photoconductivity. A photoresistor can be used in. Laser Tripwire: This project is a laser tripwire utilizing a lot of cardboard, a laser diode, and an photoresistor with a Particle Argon microcontroller. When something breaks the beam, the Arduino triggers a buzzer alarm.