librfm

About

Static avr-libc library providing basic support for RFM69 radio modules.

This is work in progress. Simple Tx-Rx with response works so far.

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

TODO

• Add support for RFM9x (LoRa)

Usage

1. Include librfm.h and librfm.a in the project
2. To make the library device and CPU frequency independent, the _rfm* functions in librfm.h must be implemented in the application

Range

Setting RegPaLevel to 0x5f, which gives +13 dBm with PA1, indoor range is very good and in an actual "field" test, packet reception was still reliable with an RSSI of about -90 dBm at about 2.2 km distance - with simple wire antennas. What would be the range with +20 dBm and decent antennas?

Susceptibility to Temperature Changes

With the default frequency deviation of 5 kHz and receiver bandwidth of 10.4 kHz, packet transmission is very unreliable and fails completely for me; when the temperature of the transmitter is below 10°C and above 40°C, while the receiver temperature is at 20°C. The receiver does not seem to be prone to temperature changes.
Increasing frequency deviation to 10 kHz and receiver bandwidth to 20.8 kHz, temperature susceptibility is eliminated; when testing with transmitter temperature from -20°C to 50°C, packet transmission is perfectly reliable.

Frequency Deviation = 10 kHz (transmitter)
RegFdevMsb = 0x00
RegFdevLsb = 0xa4

Receiver Bandwidth = 20.8 kHz
RegRxBw = 0x54