Using USB Bluetooth receiver with speaker

Discussion in 'The Projects Forum' started by tjohnson, Jan 27, 2016.

  1. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    The speaker I'm talking about is the one I posted in the completed projects collection:
    [​IMG]

    I want to add Bluetooth support to it (usually after I think I've completed a project I decide I want to add something :rolleyes:), so I bought this cheap USB Bluetooth receiver. My plan was to remove the plastic casing and the USB plug and add it to my circuit, but I found out that this doesn't work. When the speaker and the Bluetooth receiver are plugged into the same power source, there seems to be a ground loop, because no sound comes out of the speaker.

    The instructions on the plastic packaging for the Bluetooth receiver say:
    • For speakers without a USB port, connect the 5V USB plug to a charger, then connect the speaker's AUX port.
    • For speakers with a USB port, connect the device to the speaker's USB port, then connect the speaker's AUX port.
    So basically I have two options for how to power this Bluetooth receiver. I can either connect it to a cellphone charger or USB power bank, or I could add a USB port to my speaker which would require a DC-to-DC converter to prevent the ground loop. I think I would also need to use a voltage regulator for this second option because it might be problematic to supply 9V to a 5V USB device, but I'm not sure how to design a circuit to do all this.

    The first option is certainly simpler than the second one, but it's not as practical as I want. I don't like having to carry around a charger or power bank to use Bluetooth with my speaker. What do you think is the best way to power both the Bluetooth receiver and the speaker from a single power source? Is there some way I'm not thinking of?
     
    Last edited: Jan 27, 2016
  2. sailorjoe

    Member

    Jun 4, 2013
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    You are missing a voltage regulator to power the Bluetooth. Place the regulator between the battery and SW1A, pin 3, of your speaker circuit. Then which ever way the switch is set, you'll have 5 Volts at SW1A, pin 2. Wire that pin to the power input of the Bluetooth, and ground to ground. If this is done correctly, there shouldn't be a ground loop. Then wire the audio out from the Bluetooth to the audio in of your speaker.
    Here's an easy regulator for you.
    https://www.sparkfun.com/datasheets/Components/LM7805.pdf
     
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  3. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    Thanks for the helpful answer. Would an LM7805 output 5V to the Bluetooth receiver with either a 9V or a 5V input?

    If so, I'll want to order one. I was thinking of ordering from AliExpress, since I don't like having to pay shipping for such a cheap item and I don't have much access to electronics locally. Are they reputable enough that you wouldn't discourage buying simple ICs like this from them?
     
  4. sailorjoe

    Member

    Jun 4, 2013
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    The regulator is only between the battery and the switch. When you switch to 5 V, you don't need the regulator. And the 5 V is powering your speaker and your Bluetooth.
    You can order from AliExpress, but it usually takes a month to get the parts, and you will pay shipping, usually. I've used them a few times, and except for delivery time, I've always received what I ordered.
     
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  5. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    That makes sense. It seems like I'm going to need to add a DC blocking cap as well (I asked this question on Stack Exchange).
     
  6. sailorjoe

    Member

    Jun 4, 2013
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    I think they suggested two blocking caps, one for left, one for right. That's a good idea. Not sure it's needed, but it can't hurt.
     
  7. tophericks

    New Member

    Jan 29, 2016
    5
    0
    you don't need the regulator.
    [​IMG][​IMG]
    [​IMG]
     
  8. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    Are you sure that 9V will not harm a 5V USB device?
     
  9. sailorjoe

    Member

    Jun 4, 2013
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    Well, yes, I think you need the regulator to run off of your 9 V battery. Your Bluetooth device is clearly designed for 5 Volts from its USB connection.
     
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  10. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    It makes sense to me that I should use a voltage regulator, but there's still an additional problem. It definitely seems like a grounding problem, because even when I use a 9V battery to power the speaker, there is still no audio if the USB cable is plugged into the same power source as the Bluetooth receiver.

    I was told the following on StackExchange:
    and this diagnosis seems accurate to me, but I still have some questions about it. What uF value would you recommend using for this circuit? And would I need to use a resistor along with it like this? (I asked these questions there as well, but they seem to have gotten lost in the comments.)
     
    Last edited: Jan 30, 2016
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