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Thread: Accesory power on head unit?

  1. #1
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    Accesory power on head unit?

    Hi all,

    I want to install a bluetooth adapter to the accessory port of my 2005 Mazda5 head unit and run into a problem: I can't get it to work on the ACC power pin of the head unit, while it works perfectly on the B+ power pin. (But it then stays powered all the time, which I don't want to prevent the battery from draining)

    The schema I used to install the adapter is this one:



    I have a 12V to 5V power-converter to power the bluetooth adapter. When I connect this adapter to pins 2A and 2P, it works fine.
    But when I connect it to 2A and 2O (which I assume is a switched 12V output), the power converter does not work: it outputs about 1V instead of 5V.

    Any help would be greatly appreciated!

    Stefan.

  2. #2
    Registered Member Silentnoise713's Avatar

    2008 Mazda5 Grand Touring; 2009 Honda Fit Sport/Nav MT

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    I was bench testing my HU to hardwire a BT dongle. 2P reads 11.52 Volts and 2O reads 11.14 volts (I forgot to take amperage)... 2O would not power up the device either, not sure.

    Alternatively, you can re-pin the main harness and use 1J (Amp control, OEM config pin is not avail but the output works) or splice into 1R (ACC).
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    Flex Innovation 5 wire grounding Kit (for manual owners reduce drive-by-wire throttle lag)
    https://www.mazdas247.com/forum/show...56#post6532656



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  3. #3
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    Thanks for this info! I suppose it means that 2O is not a "real" switched 12V, but more like a 12V trigger signal. I'll try to measure at which amperage the voltage starts dropping.
    As a solution, I guess I will just try to fit the Xcarlink adapter that I've been using for years now in the head unit (where the cassette player could go)

  4. #4
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    I did some measurements. Without load, the voltage reads 12.12V. With a load of 100Ohm, it reads about 1V and so does it with a load of 1kOhm (for some reason the voltage is not stable under these loads)
    I guess this makes the ACC pin useless for powering anything at all. I'm very curious how it is used, since there are devices that are clearly triggered by it.
    Unfortunately my XCarLink adapter died somehow, so I have to find another solution. Maybe I'll just buy one of the ready-made bluetooth adapters (like http://www.carinterface.nl/mazda/16-...oradios_bt-maz)
    Are you sure that 1J does deliver enough power? (2.5 watts must be enough for my bluetooth adapter as it works on a regular USB port)

  5. #5
    Registered Member Silentnoise713's Avatar

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    Quote Originally Posted by deisz001 View Post
    I did some measurements. Without load, the voltage reads 12.12V. With a load of 100Ohm, it reads about 1V and so does it with a load of 1kOhm (for some reason the voltage is not stable under these loads)
    I guess this makes the ACC pin useless for powering anything at all. I'm very curious how it is used, since there are devices that are clearly triggered by it.
    I'd like to know too b/c this harness is also used to power the SAT radio adapter. This lead me to see if I can trick it to use SAT for power and input (no go ). As you stated, the ACC could just be a trigger and the powered device (such as the SAT receiver) internally switches to B+ for power.


    Unfortunately my XCarLink adapter died somehow, so I have to find another solution. Maybe I'll just buy one of the ready-made bluetooth adapters (like http://www.carinterface.nl/mazda/16-...oradios_bt-maz)
    I would recommend tread carefully with these. I reached out to a seller about them in the past. 1) These do NOT provide AD2P control, it is a pure Aux-in pass through via Bluetooth connection 2) you would still need to physically touch it to enable Bluetooth pairing (where would you put the ugly box?). On-top, it does not have manual controls, like the Kivino type BT unit provides (Siri/Google, play/pause/ FF/RW). One unknown is how this unit deals with ground loop buzz. I was hoping that grounding 2D, 2F, and 2G would eliminated the ground loop, but it still buzzes without the aux ground loop isolator. I was really disappointed.


    Are you sure that 1J does deliver enough power? (2.5 watts must be enough for my bluetooth adapter as it works on a regular USB port)
    Yes. But again, the stock connector is not pinned for 1J, which really SUCKS b/c this is suppose to control amps.... The connector looks like it is rebuildable so you can open it to see what type of pin is used and add it
    Last edited by Silentnoise713; 10-20-2017 at 12:19 PM.
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  6. #6
    Booga Booga? phunky.buddha's Avatar

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    Tap the 12v power port under the shifter?

  7. #7
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    Quote Originally Posted by phunky.buddha View Post
    Tap the 12v power port under the shifter?
    That could indeed be a solution, but previously I've had terrible ground-loop noise while powering an MP3 player connected to the aux-in from that 12V outlet. This noise disappeared when I powered the MP3 player via the USB port of the XCarLink (which somehow is also powered via the accessory connector of the head-unit)
    For this reason, I prefer to draw power from the head-unit itself...

  8. #8
    Booga Booga? phunky.buddha's Avatar

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    Put a noise filter on the 12v power? Use 1:1 transformer isolators on the audio outputs?

  9. #9
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    That's what I tried first, but somehow the groundloop isolator I used did not improve things much. Powering the bluetooth adapter from the head-unit immediately removed the noise.

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