There are lots of bluetooth speaker on the market today. But if you have an old mini component or a sound system that is still working and sounds good, why won’t you just upgrade it and put a bluetooth functionality? There are lots of audio bluetooth receiver on the market today.
Bluetooth Module
I used ALM-A01 bluetooth module that I bought from ALIBABA. This bluetooth module is compatible with latest bluetooth v4.0 and has aptX technology that enables you to have CD quality sound with low latency.
This module has a built-in battery charger with up to 200mA charging current but since we won’t be using a battery, we will not use this feature. To turn it on simply connect a 5V supply to the VCHG pin and PWR_ON pin.
Here’s the complete schematic of the bluetooth module without the 5V supply:
Just in case you want to use the buttons so I include it there. For this particular project I didn’t use it so I can’t guide you on using the buttons. The resistor and capacitor connected to the PWR_ON pin acts as a delay circuit for the PWR_ON pin to go high after the device is powered up. I placed this delay because sometimes the unit is not powering up. You do not need this if you will use the power button of the module. For my application didn’t use the power button because the main switch will also turn on the amplifier and the bluetooth module.
Amplifier Module
The amplifier module is a class D TPA3110 amplifier by SURE Electronics. It is capable of delivering 8W x 2 with up to 90% efficiency. Perfect for battery applications for longer battery life.
The Circuit
Since I have no much time to make my own PCB, I just order an ready made amplifier board and bluetooth module and put it in a bread board PCB. The bluetooth module I used is a ALM-A01 bluetooth module bought from Alibaba. It is a bluetooth v4.0 audio module with aptX technology which is cool! The amplifier board is a SURE Electronics TPA3110 amplifier board.
GETTING RID OF NOISE
Perhaps the biggest problem of every Audio engineers and hobbyist is getting rid of noise or hum. Working on bluetooth modules will give you more headaches because it will introduce another noise which the noise coming from the digital circuits of the module. In case you don’t know. The digital noise coming from a bluetooth module sounds like a morse code. The easiest way to get rid of noise is to use separate power source but this is not advisable because it will cost higher. The best way to solve it is via proper layout of ground connection. A star connection on the main filter capacitor is a big help in reducing noise. I will make a separate post on that if I have time.
Another headache on bluetooth audio module is the popping noise occurs between songs and also on power up. This was solved by using the balanced output of the bluetooth module to be connected on the balanced input of the amplifier. This simple means connecting the INN of the amplifier to the OUTN of the bluetooth module rather than connecting them to ground. The main reason behind it is still unknown. I will investigate further when I have time. 🙂
PCB Design
This PCB design is for a particular Customer so I wont be sharing the design files with you. Sorry folks. The photo below is the complete PCB of the bluetooth speaker project. It has a 2A USB charger, Aux input, and a Low Voltage protection circuit.
