IR beam proximity sensor

Discussion in 'The Projects Forum' started by optimus9, Oct 18, 2009.

  1. optimus9

    Thread Starter New Member

    Sep 15, 2009
    Here's my problem:

    I want to make a simple IR beam barrier proximity sensor with a range of about 15cm.
    I've bought the TIL78 IR receiver (phototransistor) & TIL32 IR emitter (IR LED), but the problem is that ambient light (& probably CFLs as well) interferes with it.
    I've also tried to cover the phototransistor & protect it with IR filters (floppy disk magnetic disk), but it doesn't help a lot.

    One possible solution is to modulate the IR LED at 38Khz & use an infra-red receiver module to decode the signal. Unfortunately, these IR modules aren't sold in my country.
    So, can anyone suggest a simple circuit whereby I can encode a signal with the IR LED & decode it with phototransistor? For the encoding, I've found circuits using 555 timers, but no decoding circuit.

    Btw, I'm using these sensors with an automated curtain system which is activated using an LDR & timer. Motor is controlled via an H-bridge I designed because I couldn't find any on-chip H-bridges. (That's the simulation circuit, contains redundant parts because some of them weren't available for sale.)