PDA

View Full Version : Bluetooth module @ 3.3 volts



ardhuru
- 27th October 2011, 14:28
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

Ioannis
- 27th October 2011, 16:00
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

ardhuru
- 27th October 2011, 17:21
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

Ioannis
- 27th October 2011, 17:40
Do these module support audio too?

What class are they?

Ioannis

dhouston
- 27th October 2011, 18:04
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).

ardhuru
- 27th October 2011, 18:06
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.dll?ViewItem&item=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.dll?ViewItemDescV4&item=200520318414&t=1311989106000&ds=0&js=-1&ssid=0&seller=egochina8848&category=4661&bv=mozilla&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

ardhuru
- 27th October 2011, 18:16
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-Bluetooth-RF-Transceiver-Module-RS232-backplane-/260879255730?pt=LH_DefaultDomain_0&hash=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 :(

Ioannis
- 27th October 2011, 18:33
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

amgen
- 27th October 2011, 21:22
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

Demon
- 22nd January 2012, 05:09
Moved from Schematics.

Robert