I'm having a brain freeze...

Discussion in 'General Electronics Chat' started by bluebrakes, Mar 11, 2010.

  1. bluebrakes

    Thread Starter Active Member

    Oct 17, 2009
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    I'm making a delay timer for my camera.

    However, i'm having a trouble coming up with a circuit to sort my problem out.

    Basically, I need a circuit, where the output is low.
    Once a a trigger signal has been recieved, it waits for the delay period (adjustable from 1ms to 1 second) to elapse, then puts the output to high for a period of 20ms.

    I have thought about using a 555 timer in monostable mode, but I can't get my head round the fact it needs to be low, once triggered, still low until the delay period has elapsed.

    ideally, I need it to be simple as possible. Although using a PIC microcontroller is looking more suitable solution.

    Any advice?
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    ...LED is off...
    Button pressed
    ...user preset time elapses...
    ...LED lights for 20ms...
    ...LED is off...

    There has to be an easier way to do this, but a 556 (or 2 555s),
    One for the user delay to trigger the other to hold the line high for 20ms

    If you were to go that route, you may consider a PIC. That way it can all be handles via software.
     
  3. bluebrakes

    Thread Starter Active Member

    Oct 17, 2009
    245
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    that's exactly it.

    Now to make something.

    Still, with an 556, how would you do it?

    If you had the first timer, for the off period and then the second timer for the 20ms. you still have the problem of the first timer being on when it's supposed to be off. I think?
     
  4. creakndale

    Active Member

    Mar 13, 2009
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    CD4538 or CD4098

    creakndale
     
  5. retched

    AAC Fanatic!

    Dec 5, 2009
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    The first 555 would hit and reset. So it will pulse the second 555 then reset to its original state waiting for the next trigger.
     
  6. bluebrakes

    Thread Starter Active Member

    Oct 17, 2009
    245
    7
    ok... i managed to find a circuit on the net that roughly did what i wanted it to do... and played about with it in multisim.

    It seems to work great in simulation mode.

    Does it look ok to everybody else?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you connect the low sides of C2 and C5 to Vcc instead of ground, that should keep the circuit from triggering when power is first applied. Then for C3 and C4, use 10nF.

    Pay attention to cap polarity. If you move the cap, connect the + side to Vcc, and the other side to where the + was previously connected.

    If you keep the low sides of C2 and C5 connected to ground, you'll need the large caps for C3 & C4.
     
  8. bluebrakes

    Thread Starter Active Member

    Oct 17, 2009
    245
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    thanks wookie.

    When you say move the caps, do you mean just swapping them to infront of R10 and R2?
     
  9. bluebrakes

    Thread Starter Active Member

    Oct 17, 2009
    245
    7
    I've found a circuit, which has been tried and tested (on a few websites)...

    Although I'm unsure which are supposed to be electrolytic capacitors.

    I'm fairly sure 10uf is supposed to be electro cap. But I would have thought there would be two.
     
  10. bluebrakes

    Thread Starter Active Member

    Oct 17, 2009
    245
    7
    ah i guess "C" would be the other one.
     
  11. bluebrakes

    Thread Starter Active Member

    Oct 17, 2009
    245
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    I built it tonight...

    tested it on the oscilloscope and it seems to work a treat...

    variable from 1 second to roughly to a 1ms. The truth will be when I come to try it out with the camera trigger. oh... and make it presentable in a box.

    A few pics so far...

    need to cut down the pot shaft, place in a module box and find a suitable knob.
     
  12. bluebrakes

    Thread Starter Active Member

    Oct 17, 2009
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    It clearly works very well! :D

    have a look at the attached picture.
     
  13. hondabones

    Active Member

    Sep 29, 2009
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    1
    Nice Job! The photo is very awesome. The circuit is quite interesting as well.
     
  14. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    Beautiful. Far-eekin beautiful.
     
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