Bluetooth module @ 3.3 volts


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  1. #1
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    Default Bluetooth module @ 3.3 volts

    Please excuse me if this should have been in the Bluetooth section.

    I just picked up some generic bluetooth modules off Ebay, at what I think is a good price (7.50 USD, free shipping). These are rated at 3.3 volts operation. I am wondering if its safe to get the 3.3 by simply dropping the 5 volts bus via a red LED? Would I need a filter cap after the LED? Also, while interfacing with TTL level circuits, such as a pic with VDD being 5, can I just use a resistor between the pic tx and the bluetooth module rx?

    I know these might not be the most elegant ways of doing things, but I'd love to start playing around with the module right away.

    Regards,

    Anand

  2. #2
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    Default Re: Bluetooth module @ 3.3 volts

    I would use a regulator for the 3.3 volts, since the drop on the LED will vary and also current on the module (Data?) may exceed the 20mA of the LEDs normal working.

    About the interface lines,, use a resistor voltage divider and you will be fine.

    Ioannis

  3. #3
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    Default Re: Bluetooth module @ 3.3 volts

    Thanks for the tips, Ioannis. I was afraid there would be no avoiding the regulator.

    In the meantime, more confusion. I did not get any documentation with the module, and the same (looking) module from different vendors have at least 2 different versions. At least the power, Tx and Rx pins are the same, but the activity LEDs and the mode control are on different pins. I suspect its absolutely the same hardware, but the firmware levels are different. Since this is such a breadboard-unfriendly module, I'd rather have the right data before I proceed, so I've written back to the vendor for the right documentation. Hopefully should get it soon.

    Regards,

    Anand

  4. #4
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    Default Re: Bluetooth module @ 3.3 volts

    Do these module support audio too?

    What class are they?

    Ioannis

  5. #5
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    Default Re: Bluetooth module @ 3.3 volts

    I agree that a regulator is the best way to go.

    If the current isn't too high, the MAX6349 LDO is SOT23-6 and only needs one 1F cap (available in 805 SMD).

  6. #6
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    Default Re: Bluetooth module @ 3.3 volts

    You know, Im not very sure, which is why I've called for the documentation. Although these are generic, depending on which one you buy, the same module might, or might not support audio. For example, min ( http://www.ebay.com/itm/ws/eBayISAPI...m=260697768531 ) shows pinouts for only power, ground, tx, rx, status LED and the mode. BUT, the same module at http://vi.ebaydesc.in/ws/eBayISAPI.d...&sd=3&caz.html has documentation available on the page that does show audio support. Another interesting feature is what they call the wireless RS232 mode, where its a drop-in replacement for serial connections, without any pairing required

  7. #7
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    Default Re: Bluetooth module @ 3.3 volts

    Quote Originally Posted by dhouston View Post
    If the current isn't too high, the MAX6349 LDO is SOT23-6 and only needs one 1F cap (available in 805 SMD).
    Right Dave, the MAX LDO looks just right, the current doesnt go beyond 20ma. In retorspect, I should have ordered these instead http://www.ebay.com/itm/Serial-Bluet...item3cbd9d88b2 ; 5v ready, and come mounted on a breakout PCB with standard 0.1' pins.

    Still might, but then I'll have to endure a 20 day wait till they arrive

  8. #8
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    Default Re: Bluetooth module @ 3.3 volts

    If you have the a 317 do it your self with 2 resistors or one resistor and a trimmer.

    Even cheaper and easier, a serial pass transistor with a bias to control the output.

    Ioannis

  9. #9

    Default Re: Bluetooth module @ 3.3 volts

    Think the BT module is about 100 MA in Xmit, also, need the SPP (serial port profile mode) on PC which just adds serial ports in Devices-ports (sort of virtual serial port). Sometimes comes with BT drivers.
    Don

  10. #10
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    Default Re: Bluetooth module @ 3.3 volts

    Moved from Schematics.

    Robert

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