KCX BT Emitter V1.1 does not reconnect

[saeugetier]

I have a KCX BT Emitter Version 1.1 (PCB says KCX BT Emitter V1.4). The BT emitter does not reconnect to the BT audio devices after connection got lost or bt emitter was reset. Is that behaviour normal?

Things I have done to reproduce the behaviour:

1.) Power BT Emitter: status is disconnected. The bt emitter prompts "ALL_DEVICES=0"
2.) Test current firmware version: "AT+GMR" --> V1.1
3.) Put bt audio device into pairing mode (tested with Sennheiser HD 4.50BTNC and Jabra Elite 75t headsets)
4.) issue "AT+SCAN" commands. The bt emitter finds a new device and connects to it.
5.) Copy the mac address into the "AT+ADDLINKADD=0x" command.
6.) Test with "AT+VMLINK?" if connection was saved: Success
7.) Turn off power of bt emitter
8.) Turn off audio device
9.) Turn on power of bt emitter
10.) Turn on bt audio device
11.) Test saved audio devices. Valid MAC Address was saved.
12.) Wait for 10 minutes for bt audio device to connect. No connection is established.

[Mark-MDO47]

When I read your description, it sounds to me as if the chip got damaged somehow or was defective or something like that. I know this is not very helpful, but that would be my best guess at what happened.
Of the 10 or so KCX_BT_EMITTERs I have had in intermittent use, I have had only one lock up on me (a version 1.7), seemingly for no reason. It was working fine then it quit and wouldn't respond and won't connect to the device it was already paired with. I assume I must have damaged it with ElectroStatic Discharge or perhaps my poor soldering skills damaged it by overheating. I have not been able to determine for sure what the problem is. Fortunately they are not very expensive and when I order them I get two or three extras to have some on hand.
Sorry I am not able to diagnose the issue any better than that.
Good luck!

[z-l-p]

I have this problem with multiple v1.7 boards in TX mode. It connects to my sink OK if I press the CONNECT button (or add MAC via Arduino), but if I let it connect automatically after a power cycle, it will seem to connect (PCB LED flashes twice, BT speaker stops searching for devices) but no audio will flow until I press CONNECT (which forces a brief disconnect / re-connect).
One clue: If I have the module's UART connected to an Arduino running the "Programming Arduino" sketch then re-connection works fine (with no interaction). But the module can't do it without the Arduino. Maybe the serial communication during setup convinces the module to re-connect? Or maybe the assertion of the Arduino TX pin as OUTPUT (low)? Very confusing.
EDIT: I tried grounding the module's RX pin (to simulate the Arduino setting this pin to OUTPUT) but it didn't change anything. As far as i can tell, the 1.7 boards are not useful unless being actively managed by a micro-controller.

[saeugetier]

I had no solution for that. My solution was to use ESP32-A1S modules with a custom code implementing audio in and Bluetooth audio transmitter. You can find my code here: https://github.com/saeugetier/audio_bt_emitter
I wrote down my thoughts here: https://timmedia.de/2024/03/27/IpodClassicMods.html