I suspect there was some other problem with the software I installed in the Heltec tracker first time round. It was, as I’ve mentioned previously, not the smoothest of processes.
Burrowing into the code, I find that values of 0 and 2 for bluetoothType indicate BLE, while 1 indicates “classic” bluetooth. For type 0, messages go through an AX25_Utils class, while for type 2 they’re left un-touched. In the menu code 0 is “BLE iPhone”, 1 is “BT Android” and 2 is “BLE Text” while anything else is “no BT”.
My second install attempt has been a little less fraught, and this time round the phone sees the Heltec. Neither APRSdroid nor Serial Bluetooth Terminal will actually talk to the Heltec, but at least they admit that it exists, which is progress. Serial Bluetooth Terminal complains “Connection failed: no serial profile found → use long click on device to define a custom profile”. That long click opens up a menu with a Custom option which requires three things, a “Service UUID”, a “Read characteristic UUID” and a “Write characteristic UUID”. At the moment I have no clue what these should be…