Datasheet

CircuitPython for RFM69

It's easy to use the RFM69HCW radio with CircuitPython and the Adafruit CircuitPython

RFM69 (https://adafru.it/BjE) 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 RFM69 radio only and will not work with the

RFM9X LoRa radios!

Design Considerations

One thing to be aware of before you use the RFM69 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 RFM69 and

CircuitPython:

You can only send and receive packets up to 60 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 RFM69 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 RFM69 Arduino library. This means by default the

module will setup the radio with the same GFSK, 250kbit/s, 250khz deviation, and bit whitening radio

configuration so it can send and receive data with itself and other RadioHead-driven modules. In addition the

CircuitPython module uses the same sync word and packet preamble (4 bytes) as RadioHead. If you want to use

different modulations or settings you'll need to configure the radio yourself (see the initialization

code (https://adafru.it/BjF) for the registers and bits to access, however you will need to consult the datasheet for

the necessary values).

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). You can however enable encryption and set an AES encryption key just like with the

RadioHead library. If you need guaranteed delivery or other advanced features you'll need to implement them in

your application code, or design your application be resilient to failures or missed messages.

Wiring With Breakout

First wire up a RFM69 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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