1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Help on LM358 based Infrared Beam Detector

Discussion in 'General Electronics Chat' started by biboymusic, Mar 11, 2018.

  1. biboymusic

    biboymusic Member

    Joined:
    May 23, 2010
    Messages:
    89
    Likes:
    2
    Location:
    General Santos City
    sensor circuit.jpg

    Can someone help me remove the delay on the circuit above? It is a infrared beam cut detector, much like a burglar alarm. It works fine except for one thing, delay on the relay.

    I'm trying to use this on a race beam-cut system and delay is causing problems. The Red LED reacts in realtime with the beam cut but the relay doesn't. I've tried removing caps but still the problem persist.

    The circuit works this way:

    1. If the beam is present, the relay is powered, meaning it is always on the Normally Closed position. If the beam is cut, power is taken off the relay. This part has no delay, relay click is instant.

    2. Delay comes when the beam is back again, it takes roughly around 1 second before you hear the relay click again.

    Since on a race, the starting line beam is reverse of everything. The beam is cut normally, and the beam comes back as you move out of the starting line (reaction time). This is the reason why I need to remove the delay. On the other beams like, midway, or finish line, the delay is not a problem since beam-cut is in realtime.

    Thank you!
     
  2. dknguyen

    dknguyen Well-Known Member

    Joined:
    May 6, 2006
    Messages:
    7,545
    Likes:
    161
    Where to the coils on the relay go to? They dissapear onto the other side of the board.

    It probably runs to the one of the Q components which would be a transistor that is being controlled. The stuff connected to the gate pin of that component is what you're interested in.

    Pine 2 on the LM358 seems unconnected. Does it go through a via or somethign to the other side of the board?
     
    Last edited: Mar 11, 2018
  3. biboymusic

    biboymusic Member

    Joined:
    May 23, 2010
    Messages:
    89
    Likes:
    2
    Location:
    General Santos City
    Thank you for replying dknguyen, the board is not double sided and Pin 2 is the trace that runs below Q8 going to C16. I suspect that it is thru the Qs and they are not labeled.

    About the relay coils, 1 pin goes to +12V source, the Ground trace goes to Q7 passing thru the Flyback diode.

    Do you think If I try removing every capacitor in the circuit one by one I would be able to find it?
     
    Last edited: Mar 12, 2018
  4. dave miyares

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    2
    Likes:
    -10


     
  5. dr pepper

    dr pepper Well-Known Member Most Helpful Member

    Joined:
    Oct 6, 2008
    Messages:
    5,077
    Likes:
    301
    Location:
    North west UK
    If you have an analog meter, try measuring the voltage on the electrolytic while interrupting the beam, if the voltage goes up & down when the relay clicks then you know its involved in that part of the circuit.
     
  6. dknguyen

    dknguyen Well-Known Member

    Joined:
    May 6, 2006
    Messages:
    7,545
    Likes:
    161
    Do a connectivity test. Find the cap connected to the pin of the Q component that the relay coil goes to.
     
  7. biboymusic

    biboymusic Member

    Joined:
    May 23, 2010
    Messages:
    89
    Likes:
    2
    Location:
    General Santos City
    I just did what you said and I got it. The smaller electrolytic cap discharges as the relay clicks. I removed it and delay was gone. Thanks.
     
    • Like Like x 2
  8. dave miyares

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    2
    Likes:
    -10


     
  9. dr pepper

    dr pepper Well-Known Member Most Helpful Member

    Joined:
    Oct 6, 2008
    Messages:
    5,077
    Likes:
    301
    Location:
    North west UK
    Super, well done.
    Glad to have been of assistance.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice