distance detector using 555 timer

Discussion in 'The Projects Forum' started by cvrider, Dec 3, 2007.

  1. cvrider

    Thread Starter New Member

    Dec 3, 2007
    I am trying to make a distance detector using IR emitter/detector. I want this application to work outdoors so I have implemented a 555 timer in the emitter circuit to create a frequency of about 4kHz. I then created the detector circuit with the photodetector and put the output into a high pass filter using an op amp with a frequency of 3kHz.

    For some reason, the detector circuit does not seem to work with the photodetector. If i hook the output of the 555 into the input of the high pass filter then the output goes high, showing the circuit works and detects the frequency. If I connect +5V to the input of the high pass filter, the output is 0V, showing the filter works again. If I test the photodetector using a resistor and power supply, it detects the IR from the emitter, so I know both emitter and detector work fine. It only does not work when I have the detector in series with the high pass filter circuit to detect the correct frequency.

    I simply hooked the collector of the photodetector to +5V and the emitter pin of the photodetector to the input of the high pass filter.

    Does anyone have any good troubleshooting steps I can take?

    The Emitter GIF attached is how my 555 is hooked up. I have a IR emitter and 470 ohm resistor in series off the output. The JPG attached is my detector circuit.
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    Is it possible that your photo-detector is so sensitive that it is being saturated by the ambient light and so it is unable to respond to the pulses from you emitter?

    You could rule this out by testing your setup in a dark room to see how it behaves.

  3. cvrider

    Thread Starter New Member

    Dec 3, 2007
    I tested this in the dark with the same result. Also, the detector works if I don't use the high pass filter (I just use a resistor to turn on an LED) in the same lighting conditions. Does my detector circuit look like it should work?