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Thread: Convert a flashing signal to a constant signal?

  1. #21
    Constant Bitrate Nobias's Avatar
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    Give this a try for the flasher..

    http://www.the12volt.com/relays/page5.asp#pts

    Use the output to drive a relay.

  2. #22
    Raw Wave god_of_cpu's Avatar
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    Awesome site!

    Anyone know how to calculate how big of a capacitor I'll need to overcome the 2.5s off.5s on though? The biggest capacitor I have is only 5000uf and the wiring diagram calls for 10k uf.

    Quote Originally Posted by Nobias
    Give this a try for the flasher..

    http://www.the12volt.com/relays/page5.asp#pts

    Use the output to drive a relay.
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  3. #23
    Variable Bitrate
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    What you REALLY need is an optocoupler. This is exactly what they are designed for. An optocoupler takes just enough voltage and current to light an LED and converts it to what is basically a closure. You can then use this closure to run a 12 volt line with relay to contol whatever you would like. Coverting the flashes to a constant signal is similar to using an optocoupler as a telephone ring detector. I'm currently unable to find the schematic lying about, but you basically need a cap, resistor, and the optocoupler. Do a google and you'll probably find it.
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  4. #24
    Constant Bitrate Nobias's Avatar
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    I think 1000uf is rough .5 seconds at 12v, so if that's accurate you'd be good.

  5. #25
    Constant Bitrate P4_2.66GHz's Avatar
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    Quote Originally Posted by SAScooby
    I thought about the LED, and alarm and then the door locks, then I come upon the same pitfalls as you have, the door locks are no good either as they lock automatically on my car after starting the car, then it hit me, install a seperate door open/closed switch on the drivers door, wire it up with the ignition switch and a relay or two and bang you open the door with ignition off pc begins booting, close door with ignition off no effect, ignition on no effect, then work out what you want it to do when shutting down (and also what power supply you have etc) you will need some other circuit that if the ignition is on and door is open nothing happens to the pc, I think three relays, a door switch and some wires will see you done

    Hope this helps
    You could've solved the auto locking doors issue by adding a relay that would trigger and stay on when the car is on and break the logic circuit.

  6. #26
    Constant Bitrate
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    Quote Originally Posted by god_of_cpu
    My car doors don't lock automatically after I start moving, so I'll probably just hook into them with a single relay or so if I can't get the alarm armed thing working...

    I was just talking to an engineer at work about this and he wasn't too optimistic about being able to do it with a capacitor since the on time is like only .5s and the off time is 2.5s. He did have what seems to be a very good seemingly simple idea... Use a timer circuit that would be triggered and to stay on for more then 2.5s (the flash interval of the alarm) it would be retriggered everytime a flash was recieved, so the only time it should go off is if the car is in the disarmed state and so off for more then 2.5s. This seems like the most practical idea so far, but I have yes to find some hardware to do it. Any suggestions? Pitfalls?
    You can use a monostable or one-shot circuit for this. With the proper circuit, it would give you a constant high output as long as the LED is pulsing. The output will drop to 0V after a short delay when the LED stops pulsing.

    You can use the popular 555 IC for this. There are lots of sample circuits for using the 555 as a monostable on the net. The time constant is 1.1RC so a 100 kohm resistor and a 33 uF capacitor will work as long as the trigger pulse occurs at least once every 3.63 seconds. Couple the 555 input pin (pin 2) to the LED via a small cap (0.1 uF) and a 10k pullup resistor to Vcc. Make sure you tap the correct lead of the LED - the one that has a fluctuating voltage on it (the 2.5V swing needed to light the LED should be sufficient to trigger the 555 if Vcc is 5V). The output of the 555 is the wrong polarity for your use, so you need to add a transistor to invert it (0V when the LED is pulsing, +12V when the LED stops pulsing). Check out this link for more info on the 555.

  7. #27
    Raw Wave
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    Yes the 555 is possible but you need to add more circuit to it to work properly.

    From what I can remember 555 :

    Its not retrigerable, you need a retrigerable monostable for your application.
    Its triggered by a falling edge, you need a rising edge trigger.
    The trigger voltage need to be lowered down to 2V or less.

    I done a quick design and a simulation and it does work...based on a diode/cap/res/transistor.

    Problem (or not) is you need a relay but that can be redesigned all depend what the OPUS trigger requirement are.

    Hmm cant post pics

  8. #28
    Constant Bitrate P4_2.66GHz's Avatar
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    I just thought of something.
    Does your car have a dome light that comes on for a certain period of time when you unlock your car?
    If it does, solution to your problem may be very simple.

  9. #29
    Raw Wave god_of_cpu's Avatar
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    I played around with the capacitor way yesterday night and potentially got it to work using the 12 DC power supply that came with my xenarc. I built the same circuit that was mentioned on the12volt.com, but I used a 4700uF capacitor. To test it I just disconnected the power manually and the capacitor seemed to keep the relay on for a couple seconds. I don't know if its good enough to last through the 2.5 off .5 on interval, but I assume that I could always add another capacitor if its not.

    Ricky327, I already have one of these and plan on playing around with it tonight:
    http://www.radioshack.com/product.as...Fid=276%2D1718
    Any chance you could e-mail me pics of your circuit diagram? [email protected]



    Quote Originally Posted by Ricky327
    Yes the 555 is possible but you need to add more circuit to it to work properly.

    From what I can remember 555 :

    Its not retrigerable, you need a retrigerable monostable for your application.
    Its triggered by a falling edge, you need a rising edge trigger.
    The trigger voltage need to be lowered down to 2V or less.

    I done a quick design and a simulation and it does work...based on a diode/cap/res/transistor.

    Problem (or not) is you need a relay but that can be redesigned all depend what the OPUS trigger requirement are.

    Hmm cant post pics
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  10. #30
    Raw Wave god_of_cpu's Avatar
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    Yeah it has a dome light, but problem is they dont just come on when arming the car. They come on in a similar way when you enter and exit not to mention i'd have to rip off my headliner to get to it. They also fade slowly off so they look real cool, but I'm sure it would make it harder to get it to a constant 12v.

    Quote Originally Posted by P4_2.66GHz
    I just thought of something.
    Does your car have a dome light that comes on for a certain period of time when you unlock your car?
    If it does, solution to your problem may be very simple.
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