Reflection Detector

Project Number: 51

OBJECTIVE: To detect if a mirror is present.

Description: Build the circuit on the left. Place it where there won't be any light hitting the photoresistor (RP) (such as in a dark room or under a table), and then turn it on. The 2.5V lamp (L1) will be bright, but there should be no sound. Take a small mirror and hold it above the lamp and photoresistor. You should hear sound now. You have a reflection detector! You can also use a white piece of paper instead of a mirror, since white surfaces reflect light.