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By Sparkfun Electronics

Wireless Audio Bluetooth Adapter w/ BC127

Courtesy of SparkFun


It all started when my friend and I were running late for a local dance competition. As soon as we arrived, my friend quickly exited the car and grabbed his phone. Without realizing it, he had ripped the audio connector off the cable while it was still connected to his phone. It was at that point that I decided to upgrade my sound system by adding an audio Bluetooth.

Completed project

Required Materials

To configure a BC127, make sure to have these parts:

To build the wireless audio Bluetooth adapter, you will need the following parts. You may not need everything though, depending on what you have and what you want to do. Add it to your cart, read through the guide, and adjust the cart as necessary depending on what you would like.

Note: In this project, I decided to use the BC127 for the audio Bluetooth. The code provided can vary depending on the audio Bluetooth that is used and the firmware version.

You will also need:

  • Speakers w/ 3.5mm Audio Jack
  • 3.5mm Audio Cable
  • 5V Car Adapter
  • Cardboard Box


You will also need:

Suggested Reading

If you aren’t familiar with the following concepts, we recommend checking out these tutorials before continuing.

Configuring the BC127 as Sink

Before I started building the project, I needed to understand the commands to configure the audio Bluetooth. The user manual was a little confusing at first so I decided to test the commands using a USB-to-serial converter and a serial terminal. Through testing, I found that the BC127 would somehow re-configure itself as a source Bluetooth and it would not accept any new connections. I also did not like having HFP profile turned on when there was an incoming call. I decided to use a microcontroller to automate the commands as soon as I was able to configure these settings:

  • Setting the Bluetooth’s Name
  • Setting as a Sink Bluetooth
  • Become Discoverable
  • Auto-connect with a Previous Paired Device
  • Turning off the HFP

Configuring the BC127 with an FTDI

To configure, a USB-to-serial converter was needed to send serial commands. A 1x6 row of the right angle header was broken off and soldered to the pins to the BC127’s FTDI port.


USB-to-serial converter needed to send commands

Note: This is only one way to connect to the device. Keep in mind that the micro-B USB connector on the Purpletooth Jamboree development board is used for firmware upgrades and they are connected to the USB data pins of the BC127.

For advanced users, you can also use a microcontroller with a serial pass-through code to configure.

Once the FTDI was connected to a computer using a mini-B USB cable and the drivers were installed, the commands were tested through a serial terminal set at 9600 baud, 8-data bits, no parity, 1-stop bits, and no flow control.

Restoring the BC127

Just in case, the BC127 was restored to its default state with the commands listed below. In order to send a command, a carriage return was required. Make sure to press “Enter” on a keyboard when typing the commands and the serial terminal was not sending additional characters. The BC127 should respond with an “OK” after each command:

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Naming the BC127

Next up was setting up the audio Bluetooth’s name to make it easier to recognize. I decided to name the Bluetooth “BlueTank1750”. To set the name of the BC127 from the default BlueCreation-XXXXXX to a custom name, the manual indicated that a set command needed to be issued with the configuration parameter equal to the new value. The following commands were issued:

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set name=BlueTank1750

Note: If you add a space between the "=" sign for the command, the BC127 will not recognize the command. It will respond with the "ERROR" notification.

To view if the name has been saved after reset, the following command was issued:

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get name

As a result, the BC127 responded with the configuration parameter and value:

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Setting the BC127 as Sink Bluetooth

To ensure that the BC127 was set to sink, the following commands were issued:

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set classic_role=0

Setting the BC127 as Discoverable

To test the BC127 with a smartphone’s audio Bluetooth, the BC127 needed to be set to discoverable by issuing the following command:

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Connecting a Source to a Sink Bluetooth

To connect, I found it easier to turn on a smartphone’s source Bluetooth and have it scan for Bluetooth signals in range. The BC127 (in this case it was called BlueTank1750) was selected from the list of available Bluetooth signals to pair and connect. Once selected, a 3.5mm audio cable and speaker were connected to the audio jack labeled “Headphone / Line Out”. Using the smartphone’s music player, a track was played. After successfully playing music, I continued on to the next configuration setting.

Setting the BC127 for Auto Connect

To make the Bluetooth auto connect every time it was powered up, the following commands were issued:

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set autoconn=1

After sending the commands, any smartphone with a “source” audio Bluetooth enabled was able to connect to the BC127 as a “sink” as long as it was connected previously. The device will remember the Bluetooth address and connect to the first audio Bluetooth in its vicinity that it remembers.

Since the reset command was issued, the BC127 restarted and automatically searched for the next available Bluetooth that it was able to remember. In this case, it was the same smartphone that was used in the previous test.

Turning Off the HFP

The last feature to implement was the configuration of the HFP. To turn off the HFP the following commands were issued:

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set enable_hfp=off

Hardware Hookup

After configuring the BC127 and testing the BC127, I decided to automate the commands with button presses using a RedBoard programmed with Arduino. The code was written and tested on a breadboard before soldering anything together as shown below:

code written/tested on breadboard before soldering

Soldering the Metal Pushbuttons

Once the code was tested and stable, I decided to use panel mount momentary metal pushbuttons. The momentary push push-button acts like a normal momentary push-button if you connect to the normally open (NO1) and common pin (C1). As a bonus, there are pins labeled “+” and “-” that connect to an LED ring.

Decided to use panel mount metal pushbuttons

I found that the metal pushbuttons also included a built-in resistor from user emc2, so the 330Ω resistor was not included when soldering to the buttons. Testing with a variable power supply, the LED did not appear to act like a short circuit when 5V was applied. The red LED was also removed since the project would always be connected to a power supply.

Component table

To connect the metal pushbuttons to the RedBoard’s female headers, 12" male jumper wires were cut in half and stripped using wire strippers. The exposed wire was threaded and soldered to each metal pushbutton’s pin. To assist in soldering, tape was used to hold down the wire and metal pushbutton.

Exposed wire threaded/soldered to pushbutton’s pin

An intentional solder jumper was added between the “-” and COM1 pin since both pins needed to be connected to GND.

Solder jumper added between “-” and COM1 pin

After testing the connections and LED with a multimeter, the solder joint was sealed with heat-shrink using a hot air rework station.

Solder joint sealed with heat-shrink


Once the parts were soldered together, I wanted to make a quick enclosure. I decided to use a red SparkFun cardboard box to hold and secure the parts.

Using the metal pushbutton's provided hex nut, two circles were drawn on the top of the box.


two circles were drawn on the top of the box

Using a coin, an additional hole was drawn for the power and audio cables.

Additional hole drawn for power and audio cables

Using a hobby knife, the holes were carefully cut. There was not a lot of tolerance available for the metal pushbutton's flange. A smaller hole was cut within the circle and adjusted as necessary when installing the metal pushbutton.

Using a hobby knife, the holes were carefully cut

Next up were the mounting holes for the RedBoard and Purpletooth Jamboree. I planned the location for each component and made sure that the components did not interfere with each other when the box was closed. Holes were drawn for the mounting hole locations and created using the “+” side of a mini screwdriver.

Next, mounting holes for RedBoard/Purpletooth

Two screws and a standoff were used for each mounting hole. The mini screwdriver was used to secure the hardware.

Two screws and a standoff used for each hole

After braiding the wires and wiring the components together, the metal pushbuttons were mounted and secured with their respective hex nut. This was a good time to add the mini-B USB and audio cable.

metal pushbuttons were mounted and secured

Before closing the box, I made sure that the wires and components had enough room and were not causing any stress to the connections.

I made sure that wires/components had enough room

For power, I decided to use a 5V car adapter with a USB port. I made sure to label the buttons and the Bluetooth's name before connecting it to my car.

I decided to use a 5V car adapter with a USB port

Example Code

Note: This example assumes you are using the latest version of the Arduino IDE on your desktop. If this is your first time using Arduino, please review our tutorial on installing the Arduino IDE. If you have not previously installed an Arduino library, please check out our installation guide.

The code to automate the features requires the SparkFun BC127 Arduino Library. Make sure to download it here:


The example code used for the wireless audio Bluetooth adapter can be found here:


The code is currently using “BlueBlock1750” as the BC127’s name and the auto-connect was disabled. Make sure to adjust the custom name and auto-connect in the bluetoothReset() function. For my car, I adjusted the name to BlueTank1750 and made autoconn=1. Once the code was adjusted, I uploaded the code to the Arduino.

Connecting Your Source Bluetooth

With the wireless audio Bluetooth adapter built, any audio Bluetooth set as a source should be able to connect and stream music. Here are some general notes to connect your source’s Bluetooth since each device can have different instructions. Most of the time, a smartphone (with an Android and iPhone) is used to connect. Any smartphone or laptop that has an audio Bluetooth should be able to connect. In this case, a smartphone was used.

General Steps to Connect

  • Press the “Discoverable” button on the BC127.
  • Turn on your device’s source Bluetooth.
  • Scan for the wireless audio Bluetooth adapter from your settings.
  • Select the BC127’s and begin pairing.
  • Once paired, connect to the BC127.
  • Open your music player app.
  • Choose your favorite track or mixtape and hit play.
  • Turn the volume up to safe levels on the speaker and phone once the music starts!

Stress Tests in the Field

After the first build, I decided to build two more adapters! Here are some quick notes on the different builds using the initial connection diagram.

High Volume of Users and Range

One of the adapters was donated to a local dance studio called Block 1750 to make it easier for users to connect to the studio speakers. A blue, big dome pushbutton replaced the blue metal push button as shown in the image below. The auto-connect seemed to cause confusion users connecting throughout the day so I decided to disable the feature in the Arduino’s code. Depending on the smartphone being used, the range varied for the Bluetooth connection. Some would work as far as the other end of the studio (about 40 feet line of sight). Other devices would work within a few feet. The BC127 seemed more reliable when it was within 4 or 5 feet away. The image below shows a user streaming music to the wireless Bluetooth adapter.

a user streaming music to wireless Bluetooth adapter

The big dome pushbutton installed on the wireless Bluetooth adapter and a user streaming music from his smartphone.

Going Portable

Since I also teach dance at different locations, I decided to make it a portable wireless Bluetooth adapter. In addition to the original design, a 1000mA rechargeable LiPo battery was included to make use of the BC127's LiPo charging feature. A red latching metal pushbutton was also connected between the battery and VIN so that power could be removed when not in use. I had a 5V step-up converter attached to the 5V Arduino Pro Mini and solderable breadboard. With this setup, the adapter can stream music for about 3 hours before the next charge.

Adapter can stream music for about 3 hours

Note: To save power and reduce the amount of parts used, the 5V step-up converter can be removed from the circuit and the microcontroller can be replaced with a 3.3V Arduino Pro Mini. Since the logic level of the Arduino Pro Mini is 3.3V, the Arduino's software serial pins can bypass the Purpletooth Jamboree's logic level converters

Jam On!

Since 2016, all three Bluetooths have been working great with amazing quality! The cardboard boxes holding the electronics have also withstood the test of time.

all three Bluetooths are working great


There were some issues that I ran into when trying to configure the BC127 and testing the BC127 initially. Below are a few tips for those that are using a BC127 audio Bluetooth in a project.

BC127 Output Error and Not Connecting to a Source Bluetooth?

If you are seeing this error with your BC127:

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It’s possible that the BC127 has somehow been set to source mode instead of sink mode. This can happen randomly or if you press and hold the momentary pushbutton labeled VREGEN “long” on the Purpletooth Jamboree. BlueCreations defines a long as holding it down for 1000ms or more. Resending the commands should fix the issue:

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set classic_role=0

Auto-Connect After the BC127 is Turned on

If the BC127 has been turned on before your smartphone’s Bluetooth is enabled, try hitting the RESET button to power cycle the BC127 so that it can re-scan through its saved list of previously paired devices. You can also power cycle or send the reset command.

Resources and Going Further

For more information on the Purpletooth Jamboree and the BC127 module, check out these documents:

Key Parts and Components

Add all Digi-Key Parts to Cart
  • 1568-1103-ND
  • H342-ND
  • 36-1547B-ND
  • 1568-1768-ND
  • 1528-1684-ND
  • SMDSW.031 1OZ-ND
  • 1691-1037-ND
  • 243-1005-ND
  • S1311EC-40-ND
  • 1568-1814-ND