Portable Bluetooth Speaker

Hi and welcome !

Here i will be sharing how I put together a battery powered Bluetooth speaker with minimum expenditure using a homemade amplifier and spare parts I had.The inspiration for this project was that I found a old speaker without an amplifier and decided to make one and i thought I would make it portable since i had some li-ion batteries from an old laptop.

A simple low power amplifier is used and I will also try to address the common noise problem faced while using cheap Bluetooth audio modules.

I am well satisfied with the outcome as it sounded better than expected and didn't have to spend much.

1. IC : LM386

2. Resistors: 10 k ohm ; 1/4W -2 nos

3. Electrolytic Capacitors: 0.1uf ,10uf, 100uf, 1000uf - 25v

4. Disk capacitors: 470pf

5. Pot : 10k ohm

6. 1w speaker

7. 3.5 mm male audio jack

8. USB Bluetooth audio receiver module

9. Battery: 3.7v li-ion or 9v battery

10. Switch

11.USB and Micro USB connectors

11. Stuff for PCB etching

So as I said I had the speaker first so I had to make a amplifier to match the speaker. The speaker was 1W 4 ohm and since it was going to be powered by a battery without any boosting circuit a low voltage low power amplifier such as the LM386 was best suited. The LM386 can power a speaker using a 12V DC supply to as low as 4V DC but beware the drop in audio quality!.

So I found a said great sounding amplifier circuit from circuit basics (circuit provided above) and wasn't disappointed when i tested it on a bread board. I put together the schematic in Proteus design suit and created the PCB layout for the same.

Then it was on to the etching process for which i recommend watching a YouTube video to better understand the steps to create your own PCB board at home or you can just use a copper dot board.

I finished the PCB and soldered the components onto it and tested it and it was prefect. For the audio input u can use a male mono 3.5 mm audio jack or just cut it off from a old earphone. Since its a mono amplifier you only need the ground (normally golden) and either left or right( red or green wire).

Next thing to do is add the USB type Bluetooth audio receiver which you can get for cheap at amazon ebay or aliexpress for which you can click the link here. Use a USB connector and solder some wire on it to power the receiver it works at 4-5 V DC. Connect the 3.5mm audio input to the amplifier at the other end.

For powering the amplifier as I mentioned i used two li-ion batteries in series to get around 8.3 V which was sufficient. Alternatively you can use a standard 9V battery. I had extra leads from one battery to power the bluetooth and from both for recharging purpose and to connect to a switch to power it on or off.

A problem the sometimes occur when using these kind of bluetooth devices is that it adds an unpleasant noise. It happens only if we use the same ground for both the bluetooth receiver and the amplifier. Adding a disk capacitor for decoupling could help by connecting it in series with the audio input to the amplifier but this also reduces the gain or rather the total volume at the output. One simple way to avoid it is by using separate sources for them. For battery powered projects if adding another battery is not possible another solution is using a isolated dc dc adapter like the B0505s - 1W Module which you can find here.

Finally I check all my connection a determined there was no potential short circuiting of the batteries ( as that can go really bad). Secure all connections with shrinking tubes or tape.

Fortunately enough everything fit inside my speaker case then I screwed it tight and powered it up. Paired the bluetooth with my phone and worked nicely. The audio quality was really good and i could raise the volume pretty high.

And that is just about all