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Thread: delay off circuit? (not for psu)

  1. #1
    MySQL Error scott_fx's Avatar
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    delay off circuit? (not for psu)

    Hey everyone,

    I am going to be installing a rearview cam that will go on automatically when i put the car in reverse but i want to also be able to touch a momentary (qtouch) switch and have the cam turn on for 20-30 seconds. Does anyone know how to do this? I want this switch to be independent of the computer so this will have to be a hardware based solution.


    Thanks,
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  2. #2
    Raw Wave rando's Avatar
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    You should be able to do that with a simple 555 timer circuit. A microcontroller is another option.

  3. #3
    MySQL Error scott_fx's Avatar
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    Quote Originally Posted by rando
    You should be able to do that with a simple 555 timer circuit. A microcontroller is another option.

    Thats what i'm looking into right now, but trying to find what i need is a llittle confusing. I'm pretty new to building with ic's but i'm not that bad at it. Do you know of any sites that have a good schematic and write up?
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  4. #4
    MySQL Error scott_fx's Avatar
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    i think i found it...20 seconds but it uses a 4013 flip/flop ic... still looking for a simpler 555 ic schematic
    http://www.discovercircuits.com/PDF-...ffwtimeout.pdf
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  5. #5
    Maximum Bitrate mushin's Avatar
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    That looks pretty straightforward, I doubt you're going to find much simpler than that.

  6. #6
    Constant Bitrate cbergeron's Avatar
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    Yep, Rando's right. You should use a 555. Look up "monostable one-shot multivibrator" on google and you should get some simple circuits like that. About 8 years ago I built a simple circuit to put my power windows down using a single touch button. It was an old Camaro with power windows, but they were slow and I hated having to hold both buttons down while they slowly came down (I lived in Florida and the car had Glass T-Tops). Anyway, long story short, using a 555, and a Capacitor/Resistor combo (for timing) you can create a simple circuit to do this.

    Kind regards,
    CB
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  7. #7
    Constant Bitrate cbergeron's Avatar
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    Ok, here's what I found via google:

    http://www.uoguelph.ca/~antoon/circ/monovib.htm

    You change the delay time by multiplying R1 and C1.

    Kind regards,
    CB
    DashPC - The Linux Car (since 1999).

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  8. #8
    Constant Bitrate cbergeron's Avatar
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    Edit:

    You'd probably be wise to clean up the input supply at 5-15v by putting the vehicle power through a 7805.

    Also, you'd have to add a simple transistor inline between the pin 3 output and the relay, because the 555 can't source enough current to power a decent relay.

    Finally, you _might_ need to debounce the switch to prevent false triggers. I experienced that only one time though, using the circuit I described (it was a long time ago ~1997). If you power the circuit from an ACCessory line (I would assume), the worst case scenario would be a 20 (or whatever) second rear-view camera view.

    Have fun!
    -CB
    DashPC - The Linux Car (since 1999).

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