Electronics > RF, Microwave, Ham Radio

Lora Messenger

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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:

That's pretty neat.
Add a driver for ATAK, and you could probably sell a pile of them.


--- Quote from: Skashkash on July 11, 2021, 12:50:14 am ---That's pretty neat.
Add a driver for ATAK, and you could probably sell a pile of them.

--- End quote ---
Originally, I just intended to design a low power emergency communication system for traveling and hiking, e.g., Death Valley National Park. I planned to design a long range UWB position system as the next project which could help people to find each other. However, I did not know a good APP which could be used as a framework for information integration.
ATAK looks powerful and funny, thank you for your suggestion! I will dig into it, maybe we will finally have a community project on Github~

There is also meshtastic.


But I've not seen any decent hardware implementations for it.

You have a little extra real-estate on your PCB, you could maybe add an optional gps receiver. 
But if the idea is that it'll always be used with a phone that has gps built in, maybe not needed.

Lord of nothing:
Well I want do some similar but just with DMR and PMR446 DMR Radios who can send and receive "SMS" (from Radio to Radio). For that I got a MMDVM_HS_Dual_Hat refuse to work right now.  :popcorn:
The major difference is on PMR446 is no real Transfer Cap. On the "licence free", ISM Bands are just <10% duty Circle that mean after sending a Message you may have to wait 6 Minutes or so until you can send another Message.
Well that sucks...
Another problem is the very low Output Power like <100mw when a PMR446 Radio can transmit with up to 500mw just a view Mhz above the 433Mhz.

How does your System Avoid taht?


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