This repo implements more than basic SX1276 operations while Learn_SX1276 shows all the basics.

SX1276

MicroPython Library for SX1276 LoRa radio modem

Features

• MAC layer (half-duplex).
  • One SX1276 can send a "REQ" packet (in a blocking way) and expect a specified SX1276 to respond with an "ACK" packet. This process is handled by this library.
  • One SX1276 can send a "BRD" packet (in a non-blocking way) and expect no "ACK" reply.
• Implement FHSS (first?)
  • FCC mandates frequency hopping if dwell time is above the threshold 400ms.
  • Large spreading factor and narrow bandwidth can significantly prolong the dwell time so that freq hopping is necessary for transmiiting large packet.

Usage

• Upload lora.py to MCUs (Heltec WiFi LoRa 32 V2)
• Run sender.py and receiver.py on two separate MCUs

My dev environment

• Two MCUs with SX1276 (ESP32: Heltec WiFi LoRa 32 V2)
• Flash MCUs with MicroPython
• Connect two MCUs to a Linux Machine with VSCode via USB
• Install Pico-W-Go extension for VSCode
• Open sender/receiver folders in two VSCode windows
• Configure sender/receiver projects for Pico-W-Go
• Specify the "Manual Com Device" in Pico-W-Go and restart the Pico-W-Go
• Play with Pico-W-Go commands

Console Output of sample code

FHSS

• To prove the point of frequency hopping, I use a RTL-SDR to monitor the spectrum. In following waterfall diagram, we see the signal hops between 914 and 916MHz as I programmed it to be.
• FHSS is not necessary if the message is short. For example, a 29Bytes packet can be transmitted under 400ms, given parameters {SF:10, BW:125kHz, CR:4/5, Header: Explicit , Preamble: 6}.
  Download the above air time calculator

Note

• FHSS feature can be turned off by only specifying one frequency in channels2Hopping / FHSS_list.
• It is meaningless to do Channel Activity Detection (CAD) before Tx because SX1276 only match elusive preambles which last few milliseconds. No good solution to do Listen Before Talk or CSMA.