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#!venv/bin/python
#
# This script is a very simple APRS-IS LoRa igate that
# runs on a raspberry pi and expects a RFM9x on the SPI bus.
#
# Also, there are two status LEDs on D23 and D24 that count
# the incoming messages.
#
# It is a send-only i-gate that uses the HTTP POST mechanism described
# on http://aprs-is.net/SendOnlyPorts.aspx
#
import datetime
import socket
import struct
import time
import requests
import busio
from digitalio import DigitalInOut, Direction, Pull
import board
# Import the RFM9x radio module.
import adafruit_rfm9x
# For APRS-IS
APRS_IS_SERVER = "france.aprs2.net"
APRS_IS_PORT = 8080
CALLSIGN = "HB9EGM-10"
# See https://github.com/aprsorg/aprs-deviceid/blob/main/ALLOCATING.md
APRS_DEVICEID = "APZEGM"
# 46°23.07' N 6°13.28'
LATITUDE = "4623.07N"
LONGITUDE = "00613.28E"
COMMENT = "RPi RFM98W Python igate, https://mpb.li/git/lora-aprs-hb9egm/tree/python/igate.py"
PASSCODE = "17832"
REPORTING_DISTANCE = "10"
def decode_encoded_position_report(packet):
"""Returns a string with decoded latitude and longitude, or raises ValueError"""
ix = packet.index(b":!/")
gps_packet = packet[ix+3:]
encoded_latitude = gps_packet[:4]
encoded_longitude = gps_packet[4:8]
(y1, y2, y3, y4) = struct.unpack("<bbbb", encoded_latitude)
decodedLatitude = 90.0 - ((((y1-33) * pow(91,3)) + ((y2-33) * pow(91,2)) + ((y3-33) * 91) + y4-33) / 380926.0);
(x1, x2, x3, x4) = struct.unpack("<bbbb", encoded_longitude)
decodedLongitude = -180.0 + ((((x1-33) * pow(91,3)) + ((x2-33) * pow(91,2)) + ((x3-33) * 91) + x4-33) / 190463.0);
return f"{decodedLatitude}N / {decodedLongitude}E"
def send_frame_to_aprs_is(frame):
headers = { "Accept": "text/plain", "Content-Type": "application/octet-stream" }
aprsauth = f"user {CALLSIGN} pass {PASSCODE} vers HB9EGM_lorapy 1.0 filter t/m/{CALLSIGN}/{REPORTING_DISTANCE}\n";
data = aprsauth.encode() + frame
print(data)
r = requests.post(f"http://{APRS_IS_SERVER}:{APRS_IS_PORT}/", data=data, headers=headers)
print(f"{r.status_code} {r.content.decode()}")
r.raise_for_status()
led_yellow = DigitalInOut(board.D23)
led_yellow.direction = Direction.OUTPUT
led_green = DigitalInOut(board.D24)
led_green.direction = Direction.OUTPUT
led_counter = 0
def update_leds():
global led_counter
led_counter = (led_counter + 1) % 4
led_green.value = (led_counter & 0x1) != 0
led_yellow.value = (led_counter & 0x2) != 0
update_leds()
cs = DigitalInOut(board.CE1)
reset = DigitalInOut(board.D25)
spi = busio.SPI(board.SCK, MOSI=board.MOSI, MISO=board.MISO)
baudrate = 5000000
last_beacon_time = time.time()
# see https://docs.circuitpython.org/projects/rfm9x/en/latest/
try:
rfm9x = adafruit_rfm9x.RFM9x(spi, cs, reset, 433.775, baudrate=baudrate, preamble_length=8)
rfm9x.signal_bandwidth = 125000
rfm9x.coding_rate = 5
#rfm9x.tx_power = 23 # default 13
rfm9x.spreading_factor = 12
# Section 4.1.1.6 - Set low datarate automatically based on BW and SF
symbolDuration = 1000 / ( rfm9x.signal_bandwidth / (1 << rfm9x.spreading_factor) )
if symbolDuration > 16:
rfm9x.low_datarate_optimize = 1
else:
rfm9x.low_datarate_optimize = 0
print("Waiting for packets...")
while True:
packet = rfm9x.receive(timeout=4, with_header=True)
if packet is not None:
packet = bytes(packet) # otherwise it's a bytearray
print("{}: {}".format(datetime.datetime.now(), packet))
#print(" {}".format(" ".join(hex(x) for x in packet)))
if b":!/" in packet:
print(decode_encoded_position_report(packet))
try:
# Prefix igate path
path, _, message = packet[3:].partition(b":")
new_frame = path + b",qAO," + CALLSIGN.encode() + b":" + message + b"\n"
send_frame_to_aprs_is(new_frame)
except Exception as ex:
print("Error sending position report to APRS-IS")
print(ex)
print(" RSSI: {}".format(rfm9x.last_rssi))
print()
update_leds()
now = time.time()
if last_beacon_time + 1800 < now:
last_beacon_time = now
packet = f"{CALLSIGN}>{APRS_DEVICEID},qAC:={LATITUDE}L{LONGITUDE}&{COMMENT}"
try:
send_frame_to_aprs_is(packet.encode())
except Exception as ex:
print("Error sending beacon to APRS-IS")
print(ex)
except RuntimeError as error:
print(f'RFM9x Error: {error}')
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