Add raspi igate script

2 files changed, 135 insertions, 0 deletions

diff --git a/README.md b/README.md
index 9219919..260cb0b 100644
--- a/README.md
+++ b/README.md
@@ -9,3 +9,18 @@ Try to follow https://aprs434.github.io/
 Contains STM32F103, u-blox NEO-M8N, RFM98W 433MHz LoRa Module and AFT09MS007NT1 PA:
 
 ![3d view](tracker-kicad/20230709-tracker-kicad-3d.png)
+
+## i-gate
+
+`python/igate.py` contains an APRS-IS i-gate that uses a RFM98W on a Raspberry Pi.
+It only forwards position reports.
+
+### Installation
+
+Configuration: Modify the CALLSIGN and PASSCODE inside `igate.py`
+
+    cd python
+    python3 -m venv venv
+    venv/bin/pip install -r requirements.txt
+    ./igate.py
+
diff --git a/python/igate.py b/python/igate.py
new file mode 100755
index 0000000..9466304
--- /dev/null
+++ b/python/igate.py
@@ -0,0 +1,120 @@
+#!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 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
+#APRS_IS_PORT = 14580
+CALLSIGN = "HB9EGM-10"
+PASSCODE = "22681"
+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";
+
+    # Prefix igate path
+    path, _, message = frame[3:].partition(b":")
+    new_frame = path + b",qAO," + CALLSIGN.encode() + b":" + message + b"\n"
+    data = aprsauth.encode() + new_frame
+
+    r = requests.post(f"http://{APRS_IS_SERVER}:{APRS_IS_PORT}/", data=data, headers=headers)
+    print(f"{r.status_code} {r.content.decode()}")
+
+
+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():
+    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
+
+# 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:
+                    send_frame_to_aprs_is(packet)
+                except Exception as ex:
+                    print("Error sending to APRS-IS")
+                    print(ex)
+
+            print(" RSSI: {}".format(rfm9x.last_rssi))
+            print()
+
+            update_leds()
+except RuntimeError as error:
+    print(f'RFM9x Error: {error}')