PhotoSense Driver Board

Discussion in 'General Electronics Chat' started by amirsami, Dec 21, 2013.

  1. amirsami

    Thread Starter New Member

    Dec 19, 2013
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    Dear All
    I have a packing machine which uses a photo-sensor to detect a black mark on the packing paper to drive a motor for advancing the paper roll. The relay driver board for this sensor stopped working and I am unable to make it to work. So I traced out its layout and through a little effort was able to reconstruct its circuit diagram. The board uses a simple 555 timer to process the input signal from the photosensor and drive a relay which in turn drives a contactor which drives the advancing motor. Looking at the circuit, it appears to be a complicated version of a monostable one-shot (the process is repetitive; everytime the sensor detects the black spot, it runs the motor to advance the packing paper).

    Can someone please look at the circuit and let me know how the 555 is functioning for my better understanding.

    Thanks
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,813
    1,105
    I think there must be errors, particularly component values, in the above circuit. The circuit as shown doesn't work in simulation. I'm assuming the photo-sensor provides a negative pulse to ground when activated? Check the values of the resistors linking the sensor to pin 2 of the 555. Are the 555 pins 2 and 8 really linked together?
     
  3. amirsami

    Thread Starter New Member

    Dec 19, 2013
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    0
    Hi Alec_t,
    Thanks for the reply. You are right, there are errors in the diagram. Sorry my mistake. When I hacked this circuit, I simply drew the PCB on paper and mirrored all the components on to it. The problem started when I used a schematics drawing program and went about placing everything like in a proper schematic. I am retracing all points and will post the correct diagram as soon as I get it done.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,073
    3,846
    I would guess that the black line causes a negative going pulse.
     
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