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how to make the stereo stay on with key out?

Posted by 92gsxbafaro, Jul 6, 2012

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  1. 92gsxbafaro

    92gsxbafaro Proven Member

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    So on newer cars i like how you can have the key out of the ignition and have the stereo stay on untill a door opens, so i figure why not do it on a 1g.. im just looking for advice about how to do this. any help would be awesome thanks! :rocks:
     

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    1992 Mitsubishi Eclipse GSX
    13.721 @ 102.05 · 1G DSM
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  2. bryanwheat

    bryanwheat DSM Wiseman

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    Newer cars have a body control ecu that controls things like that. You would have to build some kind of custom electronic board to make this possible.
     
  3. 92gsxbafaro

    92gsxbafaro Proven Member

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    any insight on building the board to do that? i think the work would be worth it
     

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    1992 Mitsubishi Eclipse GSX
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  4. crazyquik22023

    crazyquik22023 Proven Member

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    Just curious, what would be the advantage of this. Why not just keep the key in the ignition?
     

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  5. Colt4G63 also

    Colt4G63 also Proven Member

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    I would like to know how/why this would be worth any amount of work too.
     

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  6. 92gsxbafaro

    92gsxbafaro Proven Member

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    I just think its nice it brings a hint of modern to an older car. makes it seem nicer and yes you never know when you will need your keys for something.. haha
     

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    13.721 @ 102.05 · 1G DSM
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  7. Groundation

    Groundation Proven Member

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    You can connect the acc (I think thats it) wire on the head unit to a 12v constant on source. That way the stereo will stay on even if the key is out of the ignition. If you do that though you will have to turn the head unit off manually every time. It will take some creativity if you want to have the head unit turn off when you open the door, I have no idea how to do that.
     
  8. 91-GS

    91-GS Proven Member

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    Radioonuntilldoorisopen.gif

    When key is turned, it switches a relay (or a transistor) to ON. Now said relay is in closed loop and will stay ON indefinitly regardless of key position. Since it is ON, so is the radio. Whn the door is opened and a door switch completes the circuit for the lights (grounds it) and also grounds the relay loop. The relay looses power and switches to OFF, turning off the radio. The capacitor in the grounding circuit prevents sparks and the diode prevents back-feed from lighting circuit so lights/radio don't stay on all the time.

    This is a very BASIC circuit that will get the job done, although if the key is left ON when the door is opened it will blow a fuse since it will be a constant dead short. One of ways around it to have a pushbutton instead of the "key" switch. Will turn off when a door opens.

    Hope this helps to get you started. *I am not responsible for any potential damages* so do this at your own risk and test it with something like a test light or a volt meter first.
     
    Last edited: Mar 3, 2013

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    1991 Mitsubishi Eclipse N/T
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  9. 92gsxbafaro

    92gsxbafaro Proven Member

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    How could I have it so I dont bloe a fuse with the door open and key on
     

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  10. 91-GS

    91-GS Proven Member

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    Radioonuntilldoorisopen2-1.gif

    This should do!
    In this version when the key is ON, the door switch is disconnected and will not ground the system. When the key is turned OFF, the system stays in the loop and the radio is ON. When a door is opened with key OFF, the system exits the loop and shuts down the radio. With the key ON opening the door does nothing and the radio stays ON. :thumb:
     

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    1991 Mitsubishi Eclipse N/T
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  11. Sullbren17

    Sullbren17 Proven Member

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    You could run a wire from your battery to a fuse block, then just run your power wire on your stereo to that fuse block then hook it up to a switch or something? Idk why you would want to do that when all you have to do is turn the key... My freind has his stereo like that in his 66 mustang but I think it's pointless.
     
  12. luv2rallye

    luv2rallye DSM Wiseman

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    Seems to me you've got a problem with your design:

    1) Once the key is turned on it trips both relays which then has the battery feeding back to keep both relays (and radio) on forever regardless of what is then done with the key or door switch.
     

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  13. VR4 Kev

    VR4 Kev Proven Member

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    RadioOnwithKeyOff-RelaySetup_zps8fe1d1f6.png

    This should work for you.

    - Key provides direct power to radio like factory and also energizes the left relay.
    - Left relay load side feeds +12V to second relay load side and out through 87a (normally closed terminal).
    - 87a then feeds radio power and also feeds power back to first relay switch side. When key is turned off this keeps left relay energized.
    - To kill the radio the right relay is energized by the door switch thus killing power to the 87a terminal and killing power to the left relay and radio.

    I have not had a door switch out on a DSM but on a 3000gt they are 2 terminal.
    - One terminal is connected between both doors for interior lights and the other is separated between doors for the body computer.
    - You can use either wire but I would recommend using the common wire so if a passenger is sitting in vehicle, removes keys and opens the door the radio dies without having to go open the driver door.
     
    Last edited by a moderator: Jul 10, 2014
  14. luv2rallye

    luv2rallye DSM Wiseman

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    VR4 Kev: One thing about this circuit is that if the key is left on while door is opened, all the radio power is going through the diode. This is not advisable as the diode would have to be a high current carring one (expensive) and there would be a voltage drop across it reducing voltage at the radio. And this is a valid case as doors can often be opened while car is running. Also the diode would burn out if it's not a high enough current rated one.
     
    Last edited: Mar 3, 2013

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  15. 91-GS

    91-GS Proven Member

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    Radioonuntilldoorisopen2-2.gif

    Added another diode to prevent the backfeed issue that Luv2rallye pointed out.

    VR4 Kev, factory door and hatch swithces on a DSM (at least on 1G) are single wire. The wire becomes grounded when a door is opened. "Hatch open" switch is in the latch itself, but works the same way.
     

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  16. luv2rallye

    luv2rallye DSM Wiseman

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    91-GS: You still have some of the same problems:

    1) Your diodes are reversed biased so nothing is going to happen other than the left relay activating (diodes were also backwards in post 13 and 15 too).

    2) Even if you turn the diodes around, the right relay once activated will stay activated forever because pin 87 is connected to pin 85 which holds it. And then removing the key would deactivate the left relay which would cause a short through the diode on it when the door is opened.
     

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  17. 91-GS

    91-GS Proven Member

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    :ohdamn:

    Looked up the diode diagram, it showed that electricity flows opposite of how triangle points. Will double check.
    I'll keep thinking about the setup, hopefully will think of something better.

    Edit: Would adding a resistor between "Key" and Pin 30 on left relay help? Thinking that since electricity flows through pass of least resistance, it will go into the relay (and flip it) instead of shorting out through a resistor.
     
    Last edited: Mar 3, 2013

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    1991 Mitsubishi Eclipse N/T
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  18. VR4 Kev

    VR4 Kev Proven Member

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    RadioOnwithKeyOff-RelaySetupRev2_zps1b8a7412.png

    Revision 2! Now without diode on the 12V key wire.
     
    Last edited by a moderator: Jul 10, 2014
  19. luv2rallye

    luv2rallye DSM Wiseman

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    No, current flows the direction the arrow points when the arrow side is at least 0.7v
    more positive than the vertical bar side (0.7v for silicon diodes which is the most common type). So for a diode to be turned on (forward biased), it's easiest to think of it as needing positive on the arrow side (aka anode) and negative on the vertical bar side (aka cathode which is a band on the end of the diode). And current can never go the other way (against the arrow).
     

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  20. luv2rallye

    luv2rallye DSM Wiseman

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    VR4 Kev: BTW in your diagrams you have your relay pins 85 and 86 reversed. The cathode of the relay's internal flyback protection diode is on pin 85, not 86. Just reverse the numbers and you'll be ok.
     
    Last edited: Mar 6, 2013

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  21. Colt4G63 also

    Colt4G63 also Proven Member

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    I have a system like this wired up in my winter beater to keep the power supply to my laptop dock in the trunk on after I turn the key off. I used relays and a light emitting diode (so I know when it's on), but I don't recall all the specifics right now.

    I do remember that I used pin 87a to keep the other relay locked in a loop mode, and when the shutoff relay grounds, it pulls the switch off pin 87a, breaking the loop.
     

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  22. luv2rallye

    luv2rallye DSM Wiseman

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    VR4 Kev: Your relay on the right does absolutely nothing since pin 87 has +12v whenever the key has +12v. You can just replace that entire relay with a red vertical line from key +12v and have the same thing.

    The rest of your circuit is the same as your post 18 one, just without the series radio diode and looks off hand like it should work (kind of a set/reset flip-flop with two relays. :D) - I'll think about it some more but so far looks good. However pins labels 85 and 86 still need to be reversed.
     
    Last edited by a moderator: Jul 10, 2014

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  23. luv2rallye

    luv2rallye DSM Wiseman

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    Yes, that's exactly what VR4 Kev does in his.
     

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  24. Colt4G63 also

    Colt4G63 also Proven Member

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    Ok well I'm way too tired to examine the diagram, but I can say the theory is sound; it's been working in my car for with two relays years.
     

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  25. 91-GS

    91-GS Proven Member

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    Radioonuntilldoorisopen2-3.gif
    Have revised the diagram one again. The diode is pointing the right way now.

    In this version the key turns ON left relay so the door does not affect anything, the key also turns ON the right relay, making it go into a loop while turning ON the radio. With the key OFF the radio and right relay will stay ON untill a door is opened, grounding the right relay and braking the loop, turning everything OFF. Key overrides the door so if a door is open and the key is turned, the radio will be turned ON.
    The resistor in the circuit "persuades" the power from the key to go through right relay instead of doing into the radio. Also give the radio more juice, limiting flow throught right relay.
     

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    1991 Mitsubishi Eclipse N/T
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