Utilities to help program the KCX_BT_EMITTER module. Collected here to make them easier to find.

Note: These utilities were developed by me for the Rubber Band Gun (RBG) project https://github.com/Mark-MDO47/RubberBandGun

The KCX_BT_EMITTER Bluetooth Audio Transmitter Module receives line-level (not speaker-level) stereo audio in and transmits to a Bluetooth receiver (speaker, headphones, etc.). Be sure to connect the audio (analog) ground and do not connect audio ground to digital ground. Also due to latency in packetizing/depacketizing the Bluetooth audio, it is best to turn off any parallel wired speaker if using the Bluetooth audio at the same time.

This chip works great! It is not the very latest Bluetooth spec so it doesn't work with every single Bluetooth speaker, but it works with many and then it sounds great. One downside is that it is so small that the soldering is a challenge for me.

This Bluetooth Module uses an "AT" command set to program it to connect to your speaker and not others. Included in this repository is Arduino code (ProgrammingArduino.ino) that is used to program the KCX_BT_EMITTER. This can be used to store information about your Bluetooth speakers and/or headsets that will stay in the KCX_BT_EMITTER even after power off/on; the KCX_BT_EMITTER will scan for the matching speakers/headphones and connect only to items in that list.

Note that the KCX_BT_EMITTER expects 5V inputs for the serial port. I have heard of problems when trying to use an ESP32 as the programming Arduino. The code itself should work on an ESP32, but the ESP32 boards I know of have 3.5 V outputs. As the first document below says: "The Programming Arduino should be a type of Arduino that uses 5 Volt interfaces. For example, an Arduino Uno or an Arduino Nano Classic."

That is why I used a cheap Arduino Uno or Arduino Nano clone, which seems to me to be the simplest. Alternatively (although I have not tried this), you could potentially use the ESP32 by passing the serial transmit to KCX_BT_EMITTER signal through a 3.5 V to 5 V buffer driver and vice-versa for the return signal. If I was doing this alternative method, I would be sure also to provide 5 V power to the KCX_BT_EMITTER.

The following document describes using this capability:

• https://github.com/Mark-MDO47/BluetoothAudioTransmitter_KCX_BT_EMITTER/blob/master/ProgrammingArduino_SerialMonitor_SampleOutput.pdf

Information on the Bluetooth audio transmitter module is found here (along with ordering info)

• https://www.aliexpress.com/item/33058710334.html

Best information on the Bluetooth module I could find is here; need to translate from Chinese (see next link)

• https://item.taobao.com/item.htm?spm=a21wu.12321156-tw.0.0.7e76d1c7xEOcFZ&id=570274835710

Some more usage info on the Bluetooth module, especially English information on controlling with serial AT commands

• https://www.electro-tech-online.com/threads/kcx_bt_emitter-low-cost-bluetooth-bt-audio-module.158156/

Look in the comments in ProgrammingArduino.ino to see my interpretation of the AT commands

• https://github.com/Mark-MDO47/BluetoothAudioTransmitter_KCX_BT_EMITTER/blob/master/ProgrammingArduino/ProgrammingArduino.ino