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Thread: Headunit power-off delay circuit?

  1. #1
    Bannered takai's Avatar
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    Headunit power-off delay circuit?

    With the new OS upgrade for my Android head unit it has started to do weird things when it is rapidly turned on and then off mid boot. Such as when you start the car and the key goes through ACC and starts booting the headunit. So what im after is a circuit to delay the power-off of a headunit, basically to keep a relay latched for 5s or so after the ACC has been turned off. I know this will stop it shutting down for 5s at the end, but at least it will keep it going at the start.

    Before i build my own, i thought there might be something off the shelf out there. Otherwise its probably going to be a diode and capacitor to latch a relay.
    Chris
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    Gas Turbine enthusiast da9jeff's Avatar
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    Turbo timer?

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    What's that whooshing? Aaron's Avatar
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    Jaycar has a couple of different modules you could use - about $40
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    No I'm Not Shonky Shonky's Avatar
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    https://www.amazon.com/PAC-TR-7-Univ...ibutes=desktop
    http://www.pac-audio.com/PACProductD...ons_010505.pdf

    A few on ebay
    https://www.ebay.com.au/sch/i.html?_...c+tr-7&_sop=15

    semi complicated and has a bunch of configurable modes but will do what you want with a configurable timeout without fucking around with kits from electronics stores.

  5. #5
    Bannered takai's Avatar
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    The TR7 seems to do only 3s for time off delay, and yeah, complex as all get out.

    Surely something like this top circuit is easier: http://blog.iharder.net/2010/07/29/r...tart-your-car/
    Chris
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  6. #6
    No I'm Not Shonky Shonky's Avatar
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    3 timers in one should do it, rather than the delayed turn off mode.

    Yep, exactly that kind of circuit was my next suggestion if you're comfortable with the electronics.

    You might be able to run the output of the cap direct to the accessory line. Only issue will be how much the head unit draws on the accessory line. If it's too much, the capacitor might have to be bigger than practical. Got a multimeter you can measure it with?

    Then you'll need to get into having the capacitor driving a transistor to switch a relay or similar like the circuit you linked to. Keep the relay small in or the cap will again likely have to be too big. Standard automotive type relays will be a relatively heavy load I'd say. I'd measure the accessory load first - it might surprise you.

    How long does the delay need to be?

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    Registered User aerobrick's Avatar
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  8. #8
    No I'm Not Shonky Shonky's Avatar
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    Quote Originally Posted by aerobrick View Post
    Close but not what he wants. He wants instant on and delayed off. There's probably a variant that does it.

  9. #9
    Bannered takai's Avatar
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    Actually delayed on would work too, just stop it from starting to boot when the key passes through ACC... I can live with a 1-2s delay if i only want to listen to music in ACC. Hell the headunit has a 30s boot time anyway.
    Chris
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  10. #10
    No I'm Not Shonky Shonky's Avatar
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    Yeah thought of that. But if you had it on accessories and then went to start the car some time later, it would drop out, shutdown and reboot? Or shutdown and stay shut down (would would be a pain in arse). Depends a bit on its logic.

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    http://www.ebay.com.au/itm/DC-12V-Po...IAAOSwnHZYSXvw

    I use one of these to control my roller door.. It will do what you want.
    Last edited by uuheels; 08-06-17 at 10:34 AM.
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  12. #12
    Bannered takai's Avatar
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    Quote Originally Posted by Shonky View Post
    Yeah thought of that. But if you had it on accessories and then went to start the car some time later, it would drop out, shutdown and reboot? Or shutdown and stay shut down (would would be a pain in arse). Depends a bit on its logic.
    Yeah, but that should drop the ACC and reset the circuit. The problem isnt having it reboot on starting, its having it reboot while its already booting the first time. Found one for $1.47, ordered it, will give it a go.
    Chris
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    AE86 race car thread is finally up to date | Supposedly i have a new daily project too
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  13. #13
    No I'm Not Shonky Shonky's Avatar
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    I think you meant "shouldn't drop the ACC..."? Isn't that the whole problem at the moment? It drops ACC temporarily when you start?
    Last edited by Shonky; 08-06-17 at 02:03 PM.

  14. #14
    Bannered takai's Avatar
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    Yeah, but if the ACC never comes on while cranking then it is a non issue. The only issue i can see here is if i put it to ACC and let it partially start before cranking the engine, but that would be an extreme rarity.

    Realistically it only has to delay the signal for 1s while the key moves through ACC.
    Chris
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    I cant get no sleep...
    AE86 race car thread is finally up to date | Supposedly i have a new daily project too
    I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself. - D.H.Lawrence

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