librfm95

About

Static avr-libc library providing basic support for RFM95 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 about -125 dBm at almost 7 km distance somewhat line of sight, with the following configuration (and as well just simple wire antennas):

• Carrier frequency: 868.6 MHz
• Output power: +17 dBm
• LNA highest gain, boost on, 150% LNA current
• Signal bandwidth: 62.5 kHz
• Error correction code rate: 4/5
• Spreading factor: 9
• Preamble length: 12 symbols
• Explicit header mode
• CRC on
• Low Data Rate Optimization

So, LoRa seems to perform significantly better than FSK - as expected - but I'm quite sure FSK can go further than 2.7 km under similar conditions.

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