Two way opto-isolators using ONLY LEDs

I mentioned on a previous post that there are few projects that involves using LEDs as light detectors – well I searched in google and well “I take that statement back!”.

This doesn’t actually really involve a microcontroller – it explains how to use LEDs as both emitters and detectors of light thus by using two LEDs we can build a two way opto isolator. By using a LED as a detector and a 4011 NAND gate to drive another indicator LED this tutorial takes you to the concept behind LED based communications – the 4011 has schmitt trigger inputs thus eliminating the undefined regions in the response of the detector LED. It also pulls down to ground one of the pins of a LED indicator through a current limiting resistor to indicate that the detector received data from the sending LED.