IR phototransistor detector

Discussion in 'The Projects Forum' started by NZMikeV, Sep 4, 2010.

  1. NZMikeV

    Thread Starter New Member

    Jun 18, 2010
    Hi There
    I am currently having a bit of a fight with an IR photo-transistor.
    The schematic is simply a 555 running as a one-shot with an LED indicator and triggered by the photo-transistor when I fire a TV Remote at it. I am using the one-shot as a sort of debounce as I am not decoding the series of IR flashes I just need to detect a signal. The Red LED lights up for about 1s when the 555 is triggered. It works fine, except the maximum range is about 1 meter. What is odd though is that if I create a series phototransistor, resistor, LED circuit. The phototransistor will respond to a remote (red LED flashes brighter) from several metres away. The other odd thing is that the 555 circuit is sensitive enough to be triggered by indirect sunlight. So amplifying the sigal from the photo-transistor will simply increase false-triggers (I believe).
    If would be grateful if anyone could point out what I am doing wrong.

    I have labelled R1 on the schematic. Increasing the value of R1 increases the sensitivity of the trigger. I am using the two-legged version of a IR phtotrans that looks like an LED.
  2. eblc1388

    AAC Fanatic!

    Nov 28, 2008
    Don't use a photo-transistor. It will be sensitive to all lighting conditions and not just the IR lights as you have found out. Perhaps you can reduce this by placing an infrared filter over the photo transistor to block off visible light.

    The other better option is to use one of the dedicated 3-pin IR detector modules and you can avoid all the noise and false triggering problem. The connection to the existing circuit is the same except that you have to connect 5V to the remaining pin. Also they work to a max. of 5.5V so you will need to place a diode in series with the 6V battery to drop the voltage down a bit.

    Try looking for 38KHz IR detector in Google. The TOS17xx series is good.


    Jul 13, 2010
    I've suffered by the same problem while developing similar project..
    As solution i've used IR PAIR, so to avoid false triggering...
    Last edited: Sep 4, 2010
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
    Just be careful, a lot of the TOS series has logic circuitry incorporated in it and does not output anything unless it "sees" what it's expecting. The last one I used in a project required 10 pulses followed by a rest of at least two pulses before it would output anything at all. It was also frequency dependant, the pulses had to be at 30 KHz.

    Likewise your TV (or whatever) remote is also going to be transmitting a pulse train and may do so only for a short amount of time until the button is pressed again.
  5. Dyslexicbloke

    Well-Known Member

    Sep 4, 2010