Light Gate Circuit

Discussion in 'The Projects Forum' started by bambicomp, Dec 3, 2008.

  1. bambicomp

    Thread Starter Member

    Sep 23, 2008
    I have got to laser beams / receivers working correctly. When beam is split i get 5 volts very clear and 0v when beam is in tact.

    I want to use one of the beams as my starting point so when it is broken it starts a counter etc.

    Then when the second beam is broken it stops the counter.

    I have put this on the forum before but didnt have much luck. Can someone give me a circuit diagram for this or explain it to me. I have heard about using flip flops etc so all help appreciated.
  2. SgtWookie


    Jul 17, 2007
    You could use your first beam sensor to SET a 4013 flip-flop. The Q output of the 4013 could be used to control the enable input of a 4518 dual decade counter that has a free-running clock input.

    Use your 2nd beam sensor to RESET the 4013 flip-flop. When the Q output falls, the 4518 will stop counting.
  3. bambicomp

    Thread Starter Member

    Sep 23, 2008
    Thanks SgtWookie. That sounds good.

    So can I then feed the output of the 4518 counter to a seven segment display?

    If so what is the maximum time length I can get? Will it be seconds or longer?

    Also how accurate will the system be? Or if I used crystals would that be better? Can I use crystals with this system to make it more accurate?