Multi Room Audio Streaming Wireless Speaker

Ashwini Kumar Sinha

321
 

Many times we did wish to stream the same song in multiple locations simultaneously. Audio streaming can be done on all speakers while connecting a single audio source to another speaker wirelessly. Multi-room audio casting devices are quite expensive. They work on WiFi and sometimes face a latency issue. Devices like Airplay M U2Stream services range from Rs.7k-Rs.20k. 

This DIY project uses a hack and achieves multiroom audio streaming at an economical cost. Multiple transmitter chips are stacked with a BT receiver chip. This chip is connected to a phone or laptop from which the original audio source is played. Upon receiving the audio signal the BT chip transmits it to multiple transmitters. These transmitters are connected to other Bluetooth speakers, which stream the original audio. Thus audio latency will not take place and the original audio will be played simultaneously. 

All these audio devices can be controlled from one casting device. Since the range for bluetooth is only 100-200metres, the distance between the speaker and reciever should technically be within this range. However, this range can be expanded in this project by using an audio repeater device. The audio repeater acts as an intermediate device between the main bluetooth and target devices. It first connects to bluetooth from the main source and then connects to the target device for audio transfer.

KCX BT Emitter is a good transmitter chip, however any other relevant chip in the market can also be used. 

Fig 1 . Prototype device without PCB
Fig 2. PCB design of device

Bill Of Material 

Designing 

The original audio is obtained from the phone/laptop that connects to the main streaming device over Bluetooth and then is sent to multiple BT transmitter chips. From these transmitter chips, the audio is streamed over multiple speakers. 

The repeater device should be set up between the source and target devices. The repeater device will first connect to the main bluetooth audio source and then using the emitter chip will repeat the connection to the target speaker, thus extending the range of BT audio transmission.

Main multi stream device

For the main multistream device, the number of BT emitter chips is directly proportional to the number of connectable devices. The repeater can add up to 4 more devices. The KCX BT emitter chip is used for reference. From the datasheet and figure 3, the KCX BT003 chip is used for connecting and receiving the audio from the original source(phone/laptop etc.). The pinouts of KCX BT 003 chip gives the DAC, audio output pins.

Fig 3. KCX BT emitter chip datasheet pinout
Fig 4. KCX BT 003 datasheet pinouts

To combine multiple BT Emitter chips, the L input of the chip has to be connected with all the other BT emitter chips. This should be further connected to the output DAC L pin of BT KCX 003 chip. The same process should be followed for the R pins, connecting it to the DAC R pin. The Vcc of all the KCX BT emitters are connected to the Vbat pin of KCX BT 003 pin header, for powering the chip. The same process is repeated for the other GND pins of all chips.

Circuit design of multiroom bluetooth streaming device
Fig 5. Circuit design of multiroom bluetooth streaming device

If a PCB is needed, the circuit design can be converted into PCB by downloading the Gerber file attached. The shape and size can be customised, here a round rectangular shape of PCB is chosen. The right footprints of other components used should be set in PCB, eg. LED bulb etc. Here the footprints of the SMD LED bulb and power header are set. The power header powers the device. After all the connections are thoroughly checked, the PCB can be sandwiched accordingly. The PCB design is shown in figure 6.

Fig 2. PCB design of device
Audio streaming device pcb
Fig 6. PCB design of the device 
Fig 7. Final design of PCB

The Gerber file can be exported to the manufacturer to order the PCB board online. Relevant layers can be selected. Aluminium generally costs less. The rate by the manufacturer also varies with respect to the colour of PCB. Do not forget to select the appropriate thickness needed.

NOTE:- The PCBs are still in the shipping process. So testing could not be done using a PCB. However, the PROJECT is FULLY TESTED without the PCB by connecting individual chips and components.

Audio Repeater Device 

An audio repeater is needed only when the streaming exceeds the Bluetooth range of the device. To make an audio repeater, the KCX BT emitter chip and KCX BT 003 chip should be  connected  as in the following circuit diagram.(Refer figure 11)

Fig 10.Audio repeater chip
Fig 11, Audio Repeater PCB
Fig 12 . Audio Repeater PCB design

Connection 

If the device is not being made into a PCB, refer figure 14 for proper connection of the components.

Fig 13.Connection

 

The chips are soldered together with thin wires, but because these are SMD chips, proper micro soldering has to be done. The LED indicator is soldered to the KCX BT 003 chip. The SMD LED is used here, however any other relevant can also be used. A small solder is placed at the terminal. Refer to figure 15.

Fig 14. SMD LED
Fig 15. SMD LED Soldered

The complete circuit now has to be powered. This can be done using the USB connection or any 5V battery with a switch. Here a hexagon shaped case is used for placing the components in. The case has been printed using a 3D printer. The LED will indicate the power of the chip and its connection with bluetooth devices and speakers. An acrylic cover on the top of the casing is used to indicate if the audio is being streamed. The BT Emitter chips are connected in triangular pattern, such that the LED indication of Emitter chip is visible. The KCX BT 003 chip is fixed on top of the triangular pattern, to receive the audio over bluetooth and transfer it to all the KCX BT emitter chips.

A transparent acrylic sheet of the same shape is cut and closed over the casing. This helps us view the LEDs from all the chips to know their relevant status.

Fig 16.Fixing the components inside the case
Fig 17.Fixing the transparent acrylic cover on case
Fig 18.Acrylic cover fixed and BT chip fixed on the acrylic cover
Fig 19.Final device

Testing 

Fig 20.Acrylic cover fixed and BT chip fixed on the acrylic cover
Fig 22. Multiple Bluetooth chips with the same name appear to pair with speaker stream to multiple speakers at same time.

The device should be powered and connected to the bluetooth receiver chip.It should be paired with the KCX BT 003 chip for the audio signal to start playing over. When the multiple bluetooth speaker is brought near to this device and powered on, the speaker will automatically connect to the device and start playing audio simultaneously. Figure 22 is a screenshot of the Alexa app that scans for bluetooth. The multiple similar names of bluetooth are devices that are ready to stream audio to multiple speakers at same time

An affordable multi speaker audio streaming device is now ready.

 

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