Write hex value to a characteristic?

Thanks for checking that - it looks likely that's the issue then.

The opcodes aren't the ones I send to the BLE stack (eg. BLE_GATT_OP_WRITE_REQ vs BLE_GATT_OP_WRITE_CMD) but I suppose it's likely that the Bluetooth stack would use its own enumerations anyway.

If you're able to compile yourself, you could change the opcode used in jsble_central_characteristicWrite and see if it makes any difference.

Otherwise it looks like I need to add code to the BLE_GATTC_EVT_CHAR_DISC_RSP handler to store whether 'write with response' is available for a specific characteristic, and then to check that when writing to see which write should be performed.

I've just filed a bug for it here: https://github.com/espruino/Espruino/iss­ues/1059