I designed a Lora Messenger which does not depend on Internet or Cellular network. In other words, users can chat with others by using this credit card size Lora device and a smartphone with Bluetooth without Internet and Cellular network.
For the hardware design, a high efficiency compact Lora PCB Antenna and an ultra-low noise figure amplifier had been designed to maximum the communication range.
For the software design, a simple Lora half duplex communication protocol had been implemented by about 600 lines of C++ code.
Current testing firmware implemented:
Lora half duplex communication protocol with timeout and re-transmitting features
Bluetooth Serial Port Profile (SPP) which provides communication capability between the phone and the Lora device.
Command Parser for executing user commands through Bluetooth.
The coverage of this credit card size Lora device was tested. In the experiment (TX:14dBm, Freq:915Mhz, Spreading Factor:12), 1500m communication distance had been tested, no timeout or re-transmitting occurred. According to the link budget, this system could reach far further than 1500m.
Demo Video
Project Page:
http://uniteng.com/wiki/doku.php?id=loramessenger:project