A couple of month ago I Bluetooth enabled my second Tinytrak 4 using a HC-06 module. It turned out this failed after a few weeks and the HC-06 is not usable for APRS.

The HC-06 started to exhibit some weird behavior. Everything being sent by the Tinytrak 4 was sent back to it by the HC-06. This caused the Tinytrak to be stuck in some sort of never ending transmit loop as it thought the frame sent back were coming from my cell phone.

I use my Tinytraks alternatively in my car when I want to test other parameter sets. Thankfully the HC-06 equipped TT4 was not the one I had in the car when this behavior started and I experienced it in the shack.

I am not sure what caused this behavior, but here is my best guess :

  • The HC-06 is in AT command mode until it gets connected by a Bluetooth device
  • As a matter of fact it will try to interpret any data sent to it over the serial interface as AT command.

My conclusion is that at some point when the TT4 was running not paired to the phone a received frame put it in some sort of undocumented mode where it just sends everything back it receives on the serial port back.

Eventually I found in a drawer a similar HC-05 Bluetooth module (I always thought I donated them to someone) I used for my first Tinytrak 4, configured it and mounted it.

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