Help with latching switch circuit?

Discussion in 'The Projects Forum' started by apqo1, Oct 6, 2008.

  1. apqo1

    Thread Starter Well-Known Member

    Oct 5, 2008
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    I'm working on a custom car and I need a switching circuit. I'm more mechanically minded than electical, so I've been unable to work it out myself. I'm hoping someone here would be willing to take a stab at it. Here's what I need:

    - Constant +12V input.
    - Two switched +12V outputs, A & B.
    - One momentary contact pushbutton switch.

    First push/release of the switch latches output A to +12V (B remains zero V). Second push switches output B to +12V only as long as the switch is held closed (output A remains +12V). Third push/release unlatches output A; circuit returns to original state.

    I would prefer to accomplish this with discrete components and relays if possible. I'm sure it could be done with a digital logic circuit, but that's way beyond my capabilities.

    Many thanks!
     
    Last edited: Nov 25, 2013
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Here is one version . Relays used are Potter & Brumfield R 10-E 1-W2,V700 24 V DC, 2P2T to select caps & desistor. Operation is : Push once[ <1 sec ],RY A latches giving continous +12 V at Output A. Second continous push closes RY B & latching RY C; output 12 V now at A & B. Releasing sw opens RY B allows third push toclose RY D releasing all latched relays except D . Releasing switch returns all to initial conditions.
    Time delay , 1+ sec. ,on RY B allows a short pulse to close A and not close B , latching D prevents inavertant re triggering. Well at least it's mostly relays . Must be a bug or in there , who can find them _no prizes.
     
    Last edited: Oct 19, 2008
  3. Bernard

    AAC Fanatic!

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    Suggestion: Add a wire or small resistor from top of RY B coil to NO contact near top of RY D; to dump charge on 2200 μ F cap. Cap 220 not needed ?
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    ' connected 4 miscelaneous relays, substitutrd a diode for 220 μF cap. & adjusted R & C values to fit relays & wala_it works. Note: no supression on coils, @ low power a little arc keeps the contacts clean.
     
  5. Bernard

    AAC Fanatic!

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    To simplify timing added transistor T
     
  6. apqo1

    Thread Starter Well-Known Member

    Oct 5, 2008
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    Great, thanks! A couple more questions...

    If I used a 20kΩ pot and a 220μF cap, the delay would be adjustable from 0 to ~4.4 sec, right?

    I'm learning schematic drawing at the same time... Could you take a look at this and see if it looks right? I added D2 to protect Q1 from RLY2's field collapse.

    Thanks again for all your help!
     
    Last edited: Nov 25, 2013
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Looks great, wire as shown on your drawing + new addition. Base dischagre current measures 3 ma, so no problem. On breadboard max R was 19 k, min 680, so your pot has it well covered. My Q is 2N3566 a distant cousin to 2N2222 so results should be similar.
     
  8. apqo1

    Thread Starter Well-Known Member

    Oct 5, 2008
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    3
    Great, I'll order up some parts and give it a try, and I'll let you know how it goes.

    Thanks again.
     
    Last edited: Nov 25, 2013
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Great. apqo1 bought parts, assembled and it works.
     
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