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Thread: Small 12v Auto circuit for on/off switch for PDC switch

  1. #1
    Regular Member markm's Avatar
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    Default Small 12v Auto circuit for on/off switch for PDC switch

    Not sure if this is even possible, I have the PDC swtich that I wanted to add to my Siggy , (just because LOL ) the PDC swtich needs the factory PDC controller to work thou .

    On its own its just a press button switch.
    IE press the button and it completes a circuit (continuity tested) and same test to light the LED. I only need 4 of the 10 wires working so basciall feed in and out, and led ,

    basicall it has four wires that I need to use

    2 pairs for the in and out feed
    2 pairs for the LED circuit

    I am looking for a small circiut that will act as a on/off switch and power the LED,

    Hope this makes sense,

    press the button in and it turns a 12v feed off ,cutting the 12v output to the PDC feed and switching on the LED light,

    Press the button again and it swtiches off the LED light and then allows the 12v output to pass through again,

    it also needs to auto reset once all power has been switched off ready to start again as I have a can bus unit cutting out at 6mph ?

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    Full Member Z80's Avatar
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    Hi,

    I just drew a sketch for you, as I may need it (though I'd rather use a mechanical latching relay rather than a D latch, as I want my settings to survive engine turbing off).



    You'll need a C-MOS (because it allows the necessary 12V - or more - power supply) D latch (CD 4013) and a couple of transistors :

    - One PNP to reverse the command signal (as Vectra console buttons work by shunting the output wire to the ground)

    - One NPN to drive an automotive relay if needed (if you're driving a digital intput, then you can directly connect to either the Q or /Q signal)

    You can light the button's LED by connecting its input to the Q output (it will then be lit when the device is "on").The button contains a serial current limitation resistor already, so you can connect it directly.

    The first resistors and capacitor network are a debounce device followed by a polarisation resistor to ensure the transitor is blocked when you don't push the button.

    The second resistor and capacitor network (connected to the latch) is the reset signal you requested. It will trigger only when turning the car's power on and last while the capacitor is charging through the resistor, then the capacitor will be fully charged and will block the current, leaving the "R" input to the groud potential. The "set" (S) input is grounded to avoid oscillations (C-MOS components are very sensitive to static electricity).

    The /Q output is looped back to the "data" (D) input so the Q output (the /Q output too, BTW) will revert each time you push the button.

    You'll need to get some ignition voltage somewhere. The cigarette lighter (black wire) should just comme handy. Its brown wire is an usable ground, BTW.

    You can drive two buttons with the Cd 4013 IC, as it contains two independant latches. If your not using the second one, then connect its "Set" (S) and "Reset" (R) pins to the +12 V and "Clock" pin to the ground to avoid oscillations.

    Please ask if you want a resizeable WMF picture instead.
    Last edited by Z80; 7th October 2012 at 12:21.

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    Im thinking what you want is a 12v relay board with push button inputs (its what i used to make the dash buttons work my headrest screens). See this thread http://www.vectra-c.com/forum/showth...62-How-would-I should help you out abit. this is my thread see post 61. http://www.vectra-c.com/forum/showth...e-thread/page2
    Last edited by MiniVauxhall; 7th October 2012 at 15:49.

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    Regular Member markm's Avatar
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    Quote Originally Posted by Z80 View Post
    Hi,


    - One PNP to reverse the command signal (as Vectra console buttons work by shunting the output wire to the ground)

    .
    I missed most of that LOL, I did notice you mentioned the switch outpots to ground, not sure if it will make any difference, the Can bus trigger wire is infact outputting to ground, I've then got this through negative to possitive relay ?

    but the rest is double ductch LOL, I'll fish out the details Ive been given to look for .

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    Regular Member markm's Avatar
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    Quote Originally Posted by cliomjh 102 View Post
    Im thinking what you want is a 12v relay board with push button inputs (its what i used to make the dash buttons work my headrest screens). See this thread http://www.vectra-c.com/forum/showth...62-How-would-I should help you out abit. this is my thread see post 61. http://www.vectra-c.com/forum/showth...e-thread/page2
    Ohh yeah, that looks good, thats the sort of thing I need,

    I'll get some of the info up in a bit . see if this makes sense

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    Regular Member markm's Avatar
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    this is what i've been given so far ? very much double dutch but kind of makes sense , I've slowly learning what it all means lol

    "What you describe is known as a holding circuit How does that work. Here is what you have:
    2 – SPST push button switches {single pole single throw} One needs to be normally on the other normally off. Or 2 SPDT {single pole, double throw}
    1 – 12 Volt relay DPDT {double pole double throw}
    One bottom energies the relay across the 12V. One set of contacts on the relay, normally off is in parallel with the push button contacts. So when you push the button, relay turns on, shunts the push button contacts, and when the push button is released the relay stays on, circuit is energized.
    The 2nd push button is in series with the 1st push button and relay coil to complete the circuit. This push button is normally on. When you push this button, it breaks the relay coil circuit and the relay turns off.
    The relay’s second set of contacts would control your external circuit, what ever that is.
    So the relay contacts, one set controls the holding circuit and LED ststus indicators. The other set of contacts control the external load you want to control & any LED ststus indictors.
    This is known as a holding circuit, or set & reset.
    This can be done with transistors as well. Also this can be done with two toggle switches (DPDT), two wires in, three between the switches, and two wires out.
    I don’t have a scanner at home so I can’t send you a schematic. If it can wait till then.
    But this is real simple two wire system. Push to turn on (one button) push to turn off, second button. If you want a single button to do both, that’s possible too using a toggle flip flop.
    "
    http://www.bowdenshobbycircuits.info/page9.htm.

    “Relay Toggle Circuit Using a 555 Timer” on “page9” should do what you want — if the 555 reset doesn’t force this circuit into the same state on every power up, then I would, instead of connecting the reset line directly to 12V, I would add a “reset delay” circuit: a resistor from Reset to +12V and a capacitor from Reset to Ground. Something like 15K for the resistor, and 0.047uF (47nF) cap"

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    Full Member Z80's Avatar
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    You can't generally control a classical relay with only one button, that's why you need a flip-flop.

    Now you also need it to be bistable. The complex capacitors/resistors/transistors setup here does it : http://www.bowdenshobbycircuits.info/page9.htm

    Fortunately, it needs the switch to trigger to the ground, so you can use it.

    The CD 4013 does all this circuit does in one IC (you even have two of them inside the same chip).

    As I said, I was looking for a latching relay to do this, as I did NOT want the state to be reset afer cutting ignition off, and I finally found a schematics doing it. The one I gave you is much simpler, as it can be resetted to always the same starting state, its power consumption is negligible (apart from the relay) and it won't heat.

    The only difficulty is to revert the signal, because the CD 4013 works in positive logic, so the clock input waits for a raising edge to trigger data input, while the Vectra button will send a falling edge, hence the transistor inverter (we could have used a CMOS inverter, but a single transistor is cheaper and takes less room).

    The resistor and capacitor are always required or you'll send a burst of signals when you'll press the button instead on just one neat signal. The resistor and capacitor then absorbs the bounces to make the button depressing more precise. You can decide not to use them, but you'll regret it...

    And the "reset on power on" cell made out of the second resistor and capacitor is required too, or no circuit whatever will ensure you always start in the "reset" state. Without it, it will just start in a random state. Is it what you really want ?
    Last edited by Z80; 8th October 2012 at 04:24.

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    Cheers All

    I would say I know what your talking about LOL but it sounds good !

    how much would something like this cost to make and where is the best place to get it made ? I have both ends to the circuit (the switch) (the Trigger wire, either Positive or negative)

    I've got a new IDC plug coming and wires as my test subject was just a standard printer IDC plug and ribbon cable which would only take 1amp at best, the new plug should be here in a day or so and new cable has also been shipped so I can finish this part, just got to find the correct wire for the illumination to the switch which I can feed from the Can Bus interface ,

    Just need the bits in the middle LOL

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    The current flowing in the switch or LED will be very low here, so you can just use a strip of used flat cable. IDC connector are self-crimping (use a small vice or a flat plier if you don't have one).

    A CD 4013 will cost something like £1.5 by 5 pieces or even by 10 on eBay... Other components will be cheaper (but will aslo probably be sold by 10, 20, 50, 100 pieces)...

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