It is the same principle in ALL Infra-Red proximity sensors. The basic idea is to send infra red light through IR-LEDs, which is then reflected by any object in front of the sensor. Then all you have to do is to pick-up the reflected IR light. For detecting the reflected IR light, we are going to use a very original technique: we are going to use another IR-LED, to detect the IR light that was emitted from another led of the exact same type! This is an electrical property of Light Emitting Diodes (LEDs) which is the fact that a led Produce a voltage difference across its leads when it is subjected to light. As if it was a photo-cell, but with much lower output current.

     Digital Thermostat with LED Temperature Display
     Thermostat Controller with Relay using LM35 and TL431
     Electronic Thermometer using LM35
     PIR Motion Detector
     Temperature Control using a DS1621 Sensor and a ATtiny 2313 Micrcontroller
     Temperature Controlled Fan
     IR Proximity Sensor
     Light / Dark Relay Switch
     Park Assist Circuit
     Homemade Metal Detector

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