Overview

This project is a Python library for using HopeRF RFM95/96/97/98 LoRa radios with a Raspberry Pi. The design was inspired by the RadioHead project that is popular on Arduino-based platforms. Several handy features offered by RadioHead are present here, including encryption, addressing, acknowledgments and retransmission. The motivation of this project is to allow Raspberry Pis to communicate with devices using the RadioHead RF95 driver along with RHReliableDatagram and RHEncryptedDriver.

Usage

Installation

Requires Python >= 3.5. RPi.GPIO and spidev will be installed as requirements

pip install raspi-lora

Getting Started

Here's a quick example that sets things up and sends a message:

from raspi_lora import LoRa, ModemConfig

# This is our callback function that runs when a message is received
def on_recv(payload):
    print("From:", payload.header_from)
    print("Received:", payload.message)
    print("RSSI: {}; SNR: {}".format(payload.rssi, payload.snr))

# Use chip select 0. GPIO pin 17 will be used for interrupts
# The address of this device will be set to 2
lora = LoRa(0, 17, 2, modem_config=ModemConfig.Bw125Cr45Sf128, tx_power=14, acks=True)
lora.on_recv = on_recv

lora.set_mode_rx()

# Send a message to a recipient device with address 10
# Retry sending the message twice if we don't get an  acknowledgment from the recipient
message = "Hello there!"
status = lora.send_to_wait(message, 10, retries=2)
if status is True:
    print("Message sent!")
else:
    print("No acknowledgment from recipient")
    
# And remember to call this as your program exits...
lora.close()

Encryption

If you'd like to send and receive encrypted packets, you'll need to install the PyCryptodome package. If you're working with devices running RadioHead with RHEncryptedDriver, I recommend using the AES cipher.

pip install pycryptodome

and in your code:

from Crypto.Cipher import AES
crypto = AES.new(b"my-secret-encryption-key", AES.MODE_EAX)

then pass in crypto when instantiating the LoRa object:

lora = LoRa(0, 17, 2, crypto=crypto)

Configuration

Initialization

LoRa(channel, interrupt, this_address, freq=915, tx_power=14,
      modem_config=ModemConfig.Bw125Cr45Sf128, acks=False, crypto=None)

channel SPI channel to use (either 0 or 1, if your LoRa radio is connected to CE0 or CE1, respectively)

interrupt GPIO pin (BCM-style numbering) to use for the interrupt

this_address The address number (0-254) your device will use when sending and receiving packets.

freq Frequency used by your LoRa radio. Defaults to 915Mhz

tx_power Transmission power level from 5 to 23. Keep this as low as possible. Defaults to 14

model_config Modem configuration. See RadioHead docs. Default to Bw125Cr45Sf128.

receive_all Receive messages regardless of the destination address

acks If True, send an acknowledgment packet when a message is received and wait for an acknowledgment when transmitting a message. This is equivalent to using RadioHead's RHReliableDatagram

crypto An instance of PyCryptodome Cipher.AES (see above example)

Other options:

A LoRa instance also has the following attributes that can be changed:

• cad_timeout Timeout for channel activity detection. Default is 0
• retry_timeout Time to wait for an acknowledgment before attempting a retry. Defaults to 0.2 seconds
• wait_packet_sent_timeout Timeout for waiting for a packet to transmit. Default is 0.2 seconds

Methods

send_to_wait(data, header_to, header_flags=0)

Send a message and block until an acknowledgment is received or a timeout occurs. Returns True if successful

• data Your message. Can be a string or byte string
• header_to Address of recipient (0-255). If address is 255, the message will be broadcast to all devices and send_to_wait() will return True without waiting for acknowledgments
• header_flags Bitmask that can contain flags specific to your application

send(data, header_to, header_id=0, header_flags=0)

Similar to send_to_wait but does not block or wait for acknowledgments and will always return True

• data Your message. Can be a string or byte string
• header_id Unique ID of message (0-255)
• header_to Address of recipient (0-255). If address is 255, the message will be broadcast to all devices
• header_flags Bitmask that can contain flags specific to your application

set_mode_rx()

Set radio to RX continuous mode

set_mode_tx()

Set radio to TX mode

set_mode_idle()

Set radio to idle (disabling receiving or transmitting)

sleep()

Set radio to low-power sleep mode

wait_packet_sent()

Blocks until a packet has finished transmitting. Returns False if a timeout occurs

close()

Cleans up GPIO pins and closes the SPI connection. This should be called when your program exits.

Callbacks

on_recv(payload) Callback function that runs when a message is received payload has the following attributes: header_from, header_to, header_id, header_flags, message, rssi, snr

Resources

RadioHead - The RadioHead project. Very useful source of information on working with LoRa radios.

Forked version of RadioHead for Raspberry Pi - A fork of the original RadioHead project that better accommodates the Raspberry Pi. Currently is a few years out of date.

pySX127x - Another Python LoRa library that allows for a bit more configuration.

Adafruit CircuitPython module for the RFM95/6/7/8 - LoRa library for CircuitPython