Bluetooth Speaker System (Audio Blobs) – B2P19

Published by frenoy on

Building a Bluetooth speaker from the ground-up is a challenging task, but thankfully, we have pre-programmed modules that can be used to make it much simpler. We will use one such Bluetooth audio module to build a Bluetooth speaker.

The BBox 2 contains two modules called blobs, which further simplifies the building process. One consists of a pre-programmed Bluetooth audio module and the other consists of two class D amplifier ICs. The Bluetooth audio blob consists of a CSR8645 Bluetooth receiver that handles all the Bluetooth related tasks and gives us the audio output.

The Bluetooth audio blob is represented as U$1 in the schematic. We connect the power pins, two status LEDs along with the volume control switches.

The MFB pin acts like an enable pin and the RC circuit consisting of R3, R4 and C3 creates a short delay which is needed as per the design spec for the CSR8645 module. The audio output is sent to the two individual amplifier ICs after passing through a capacitor which is used to block any DC component contained in the signal.

The amplifier ICs themselves are extremely simple. All they need is power and a bypass capacitor to produce an output. We add some filtering and reservoir capacitors to absorb any surges in the current, particularly at high volumes. The control pin can be used to mute the audio output and we connect this to a switch. The output from the audio amplifiers is fed directly to the speakers.

The PCB also contains 4 probe points that can be used to extract the audio signal from the Bluetooth receiver and use it in external circuits. We will be using these in the next project which creates a visual effect from the audio signal.

Assembling the PCB is not difficult but please ensure that the capacitors are placed with the correct polarity. You will also need to solder the header pins to the two blobs. Please ensure that you insert the blobs with the correct orientation and there are hints on the main PCB to help you with this. The Bluetooth audio blob requires 3.3V while the amplifier uses 5V, so ensure that you have connected the correct voltages to each of the screw terminals.

When the PCB is powered ON, the two LEDs will start to flash quickly indicating that no device has been paired with the receiver.

Head over to your Bluetooth device and select the receiver which would either show up as CSR8645 or F-3188. Once paired, the LEDs will stop flashing continuously. You will now be able to play audio from your Bluetooth device and this should playback on your speakers.

One thing to keep in mind is that the speaker enclosure plays a huge role in determining audio quality. Leaving them on your table is certainly not going to give you the best sounding audio. In fact, simply holding them with your hands and rotating them will change the way they sound. We recommend placing them in an enclosure to enhance the audio quality.

There are many ways by which you could create a DIY enclosure, you can even cut a few holes in the box and add the speakers, PCB and battery inside to create a portable Bluetooth speaker.

Alternatively, you can add the speakers to either end of a can for a better-looking system.
With that being said, lets now work on the final project which helps us create a visual effect.

Categories: BBox 2