Recently, I bought a pair of really cheap speakers. It took power from USB plug and audio input was through a 3.5mm jack.
After using them for some time I realized that these speakers were limiting freedom of my smartphone.
Solution- Bluetooth speakers.
Lets get started.
Step 1: Short Video
Here is a small video summarizing all steps.
Step 2: Understanding Speaker's Interface
In order to modify any hardware first we need to understand it. With the help of few screwdriver and some muscle I managed to take out PCB of the speaker.
PCB contains 2 audio power amplifier one for each speaker. Towards left, we have pads for VCC and GND. On upper side of audio power amplifier, we have pads for terminals of speaker. Audio power amplifier IC used on this PCB are Texas Instrument's LM4871T 3W audio power amplifiers. Towards right we have pads for audio input. On the back side of PCB, we have volume control knob and a decoupling cap.
Step 3: Bluetooth Stereo Adapter
To add Bluetooth functionality, I bought a Bluetooth stereo adapter. It took power through USB port and outputs audio on a 3.5mm audio jack. I opened it up to look at its PCB. IC used in this module was BEKEN's BK3254 and module was named as BT-163.
Step 4: Figuring Out Connection Between Speaker's PCB and Bluetooth Module
I connected speaker's 3.5mm jack to Bluetooth module and used my multimeter's short functionality to figure out connectivity between pads of speaker's PCB and Bluetooth module.
I marked names of corresponding pads on Bluetooth module using a marker along with Vcc and Gnd pins of USB port.
Step 5: Altering Connections
Now that connections were figured out. I used wire stripper and chopped off wire connecting to audio input of speaker's PCB. Conditioned them a little bit and soldered them to corresponding pads on Bluetooth module.
Next I removed USB connector from Bluetooth module using a desoldering braid and soldering iron. Once it was removed, I connected Vcc and Gnd terminals of BT-163 to Vcc and Gnd terminals on speaker's PCB. With all soldering done. I secured all connections using a glue gun.
Step 6: Putting Back Together
Finally, I tested operation of the circuit and it passed quality check without any problem. So I placed everything back inside the speaker case and that was it.
Speakers converted to Bluetooth speakers.
Thanks for reading.