A type of timer circuit for motorcycle lights

Discussion in 'The Projects Forum' started by confused_scooter_guy, Sep 3, 2009.

  1. confused_scooter_guy

    Thread Starter New Member

    May 14, 2006
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    I want to put strobing auxiliary stop lights on my motorcycle. They make a self-contained set that is powered by the brake light circuit of the motorcycle. The problem is as long as the brake light is lit (like at a stop light), the strobes keep going. Certain states have rules about how long stop lights can strobe. I was wondering if I could find a circuit that could allow the strobes to flash for a pre-determined time limit and then stop even though the circuit still had power. The timer would start again when the 12 volt stop light power is stopped and started again. It would be nice to be able to vary the length of the duty cycle. Thanks.
     
  2. jj_alukkas

    Well-Known Member

    Jan 8, 2009
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  3. confused_scooter_guy

    Thread Starter New Member

    May 14, 2006
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    I don't need the flasher. The flasher is built into the LED lights. What I need is a circuit the only passes the 12 volts through to the LEDs for a short period of time and then stops. I want the auxiliary strobe LEDs to stop strobing even though the brake light circuit still has 12 volts on it. When the brake light goes off, I want the circuit to reset and go on again the next time the brake is applied.
     
  4. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Oh, sorry then. So when you brake, you need to switch off the light after a few seconds even though it is applied, right?

    Use a 555 in monostable mode and wire the HIGH output to the lights.You can vary the duty cycle with a variable resistor. BTW what is your LED load current?
     
  5. confused_scooter_guy

    Thread Starter New Member

    May 14, 2006
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    Thank you JJ. Yes, that's exactly what I want to do.

    I don't know the LED load current, but I can get a hold of the people selling the unit and ask them. Is there a limit to what the 555 can handle?

    So if I search on "555 monostable" here on the Forum, I should find a circuit diagram, right? Thanks again.
     
  6. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Knowing the load would help decide which transistor driver to using without jumping directly to a heavy one using guesswork. The 555 can handle only 200mA, but that not a problem. I can draw up a circuit if you state how many seconds of output and how much adjustment in time you need with the LED load. Of you have a multimeter, stick it out and check how much current it draws.
     
  7. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
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    Could another approach be to get a signal that is related to either the speedometer or the rotational speed of a wheel and only flash when the bike is not stopped? That might satisfy your goals. Maybe you could find one of those bicycle speedometers that detect wheel motion with a magnet and Hall sensor if you can't utilize the bike's speedometer directly.
     
  8. bennettdan

    New Member

    Sep 7, 2008
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    Check out this websight on the 555
    http://home.cogeco.ca/~rpaisley4/LM555.html#20
    look at the Two Stage Time Delay Circuit
    You will need to add a mosfet or a solid state relay to handle the load of the light in between the output of the second 555 and the light.
     
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