Bluetooth LE Troubleshooting

Intro

Bluetooth classic is easy. Pair a device, then use it.

Bluetooth LE is a bit more difficult. The standard (4.0, 4.1, 4.2) offers different security features and bluetooth device use different subsets. Succesful connection with Bluetooth LE devices highly depends on the combination of your Bluetooth device and Android version.

The Bluetooth LE standard uses the terms pairing & bonding differently than Android, where you get a pairing request for bluetooth bonding. For simplicity I use the term pairing.

Bluetooth LE vendors

Most of the Bluetooth LE devices offering a serial service are based on these two SoC: The Bluetooth LE standard does not define a serial protocol, so each vendor defined their own GATT service + characteristic UUIDs. This app knows both and allows custom UUIDs.

Common issues

There are various complaints about the Android Bluetooth stack, e.g. here about random disconnects. In case of connection errors there are only strange error codes without description

HM-10 clone (CC41-A, BT05, ...) issues

There are different clones of the HM-10 device, typically sold under the original name. The original device uses AT commands without line feed, whereas the clones use line feed and have less and slightly different AT commands. Here you can find a comparison and the data sheets. Somewhere i read that these devices use an outdated TI library causing pairing problems.

Successfully using the clones is a game of luck, as there are several issues:

Security mode AT+TYPE1/2/3 for pairing with Pin

Stricter SCAN filter in Android 8.0

Other Devices?

If you have results for other devices, please contact me at mail@kai-morich.de