Sample program for printing QR barcode with Unitech bluetooth printer. Tested with Unitech SP319 and SP419.
Service UID: 49535343-fe7d-4ae5-8fa9-9fafd205e455
Characteristic UID: 49535343-8841-43f4-a8d4-ecbe34729bb3
ble.js based on WebBluetoothCG printer sample app.