Datasheet

CircuitPython for RFM9x LoRa

It's easy to use the RFM9x LoRa radio with CircuitPython and the Adafruit CircuitPython

RFM9x (https://adafru.it/BjD) module. This module allows you to easily write Python code that sends and receives

packets of data with the radio. Be careful to note this library is for the RFM95/96/97/98 LoRa radio only and will

not work with the simper RFM69 packet radio.

Design Considerations

One thing to be aware of before you use the RFM9x series of radios with CircuitPython are some of the limitations and

design considerations for its module. Keep these in mind as you think about projects using the RFM9x and

CircuitPython:

You can only send and receive packets up to 252 bytes in length at a time. The size of the radio's internal buffer

dictates this limit so if you want to send longer messages you'll need to break them into a series of smaller send

calls in your application code.

Receiving packets is a 'best effort' in pure Python code. Unlike the Arduino versions of the RFM9x library there is

no interrupt support which means when a packet is received it must be immediately processed by the Python

code or it could be lost. For your application it will work best to only receive small, single packet messages at a

time. Don't try to receive kilobytes of data or else you'll lose packets. This module is really intended for simple

single packet messages like 'ON', 'OFF', etc.

Sending and receiving packets will 'block' your Python code until the packet is fully processed. This means you

can't do a lot of other things while sending and waiting for packets to be received. Design your application so

the radio usage is the primary scenario and very little other tasks need to happen in the background.

The module is written to be compatible with the RadioHead RFM95 Arduino library. This means by default the

module will setup the radio with the same modulation and configuration for transmitting and receiving at the

maximum distance with LoRa support. In addition the CircuitPython module uses the same packet preamble (8

bytes) and header (4 bytes) as RadioHead. If you want to use different modulations or settings you'll need to

configure the radio yourself after carefully consulting the datasheet.

The CircuitPython module does not support advanced RadioHead features like guaranteed delivery or its internal

node addressing scheme. Only the simple 'raw' RadioHead examples are supported (i.e. broadcasting a packet

to all listening radios).

Encryption and sync words are also not supported by the LoRa radio module. You must perform these

operations yourself in your application code if they're desired.

Wiring With Breakout

First wire up a RFM9x breakout to your board as shown on the previous pages for Arduino. Note that the G0/interrupt

line is not used by the CircuitPython module and can remain unconnected. Here's an example of wiring a Feather M0

to the radio with a SPI connection:

https://learn.adafruit.com/adafruit-rfm69hcw-and-rfm96-rfm95-rfm98-lora-packet-padio-

breakouts

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