librfm95

About

Static avr-libc library providing basic support for RFM95 (SX1276) radio modules. Other RFM9x radios might work as well, but were not tested yet.

I'm impressed how well these radio modules work; the range achieved with simple wire antennas as well as the reliable packet transmission.

This is work in progress. Currently available is (FSK and LoRa):

• Transmit a packet
• Blocking receive a single packet with timeout
• Async'ly receive a packet (MCU sleeps or does something else until reception)

Usage

1. Include librfm.h and librfm.a in the project
2. Implement the _rfm* functions in librfm.h in the application (this is to make the library device and CPU frequency independent)
3. Route interrupts occurring on DIO0 and DIO4(FSK)/DIO1(LoRa) to rfmIrq()

Range

FSK

Transmitting with +17 dBm, reception stopped with an RSSI of about -125 dBm at almost 2.7 km distance - with simple wire antennas, and a low hill in between.

Compared to the RFM69 at +13 dBm, it does make it a few hundred meters further - seems fair enough!

LoRa

With LoRa, reception was stable with an RSSI of -111 dBm and +15 dBm Tx power at over 12 km distance line of sight, with the following configuration (and as well just simple wire antennas):

• LNA highest gain, boost on, 150% LNA current
• Signal bandwidth: 41.7 kHz
• Error correction code rate: 4/5
• Spreading factor: 10
• Low Data Rate Optimization

So, LoRa seems to perform significantly better than FSK - as expected - but FSK certainly can go a lot further than 2.7 km under similar conditions (plain line of sight).

Anyway, these radio modules work very well with both modulation schemes!

Here's the transmitter placed at Mont-Saint-Aubert, with a nice view to Mont de L'Enclus, were the receiver was located: