LoRa physical layer python example

This is for hobbyists or students who wish to create simple point-to-point link using LoRa physical layer.
This is not LoRaWAN.

LoRaWAN is a MAC layer (and network infrastructure) which runs on top of LoRa physical layer.

This driver operates SX1272 or SX1276. The chip type is detected on startup, meaning this driver works with both devices. This driver requires py-spidev, because LoRa radio chip operates over SPI. GPIO pin access is required for DIO0 pin and antenna switch pin (if RF switch isn't already controlled by radio chip). DIO0 pin from radio chip indicates when TX is complete or RX packet received. GPIO pin's are operated completly from user application, to allow python driver to operate on any platform which py-spidev works. In the case of raspberry pi, examples are provided using RPi.GPIO.

Installation, RPi example:

Enable SPI on RPi

py-spidev installation

sudo apt-get update

sudo apt-get install python-dev

git clone https://github.com/doceme/py-spidev

cd py-spidev

sudo python setup.py install

RPi pin connections to LoRa radio

	Pin#	Pin#
+3.3v	1	2	+5v do not use
	3	4	+5v do not use
	5	6	gnd
	7	8
gnd	9	10
	11	12
	13	14	gnd
	15	16
+3.3v	17	18	(dio0 in example)
MOSI	19	20	gnd
MISO	21	22	(ant SW in example)
SCLK	23	24	NSS-0
	25	26	NSS-1
	27	28
	29	30	gnd
	31	32
	33	34	gnd
	35	36
	37	38
gnd	39	40

Dragino board connects SPI-NSS to pin 22, requiring software controlof SPI chip select (example not provided). If you want spidev control of NSS, connect pin 24 to LORA-NSS. Dragino uses pin 7 for DIO0. Hope RF doesnt require antenna switch control from CPU, this is done on Hope RF board.

This code was tested with SX1276 Shield.

Fixed RPi pins: MOSI, MISO SCLK, NSS. Variable pins: DIO0, antenna switch LORA-RESET pin should be left floating for normal operation. On some boards, antenna switch could be driven by radio chip. On others it could be driven by CPU pin. Other boards might have antenna switch requiring more than one pin to control.

Pay close attention to schematic of your LoRa RF board for selection of RFO or PABOOST pin for transmit operation. PaSelect must be configured to match RF connection on your board (PaSelect = 1 for PABOOST). PABOOST can offer up to 100mW of transmit power, or RFO can provide 20mW at lower current consumption. If antenna switch is not correctly controlled, approximately 25dB signal loss will result. If PaSelect is not configured correctly, RF output can be practically non-existant.

Example Programs

Configuration is done by accessing properties. tx_dBm is for accessing transmit power. If your board is using PA_BOOST for TX, you can set to 20dBm. Receive mode is started by calling rxCont(), transmit is started by calling tx(<python list>)

test.py

Program demonstrating LoRa physical layer transmission and reception. Simple text command interface is provided for testing: '?' to see list of commands.

crc.py

Using PyCRC for LoRa message integrity check.

regulatory compliance

Sub-GHz rules vary of country to country for unlicensed bands. In USA, FCC rules permit operating on 902 to 928MHz band. LoRa complies with DSSS rules when when operating at 500KHz bandwidth configuration, with up to +20dBm TX power from within 902 to 928MHz, while staying on the same radio channel. Alternately using a lower bandwidth LoRa signal (125Khz/250KHz/etc) requires limiting TX duration to 400ms while randomly selecting a different frequency after that 400ms (FHSS rule). In other countries, the unlicensed RF channels can be different, in some cases requiring listen-before-transmit, or duty cycling limiting.

(edited using https://dillinger.io/)