Fall back in case of low audio

record_iss.py

@@ -0,0 +1,105 @@
+#!/usr/bin/python3
+import urllib.request
+import subprocess
+import math
+import socket
+import ephem
+import time
+import sys
+import ssl
+import os
+import signal
+import datetime
+
+LATITUDE = "52.219308"
+LONGITUDE = "4.419926"
+ALTITUDE = 20
+
+MODE = "fm"
+FREQ = "145.8M"
+RATE = "48k"
+
+FILE_FMT = "%Y_%m_%d-%H-%M-%S.raw"
+
+rtl_cmd = ["rtl_fm", "-M", MODE, "-f", FREQ, "-s", RATE]
+
+class tle_reader(object):
+    """
+    For keeping ephem two line element sets up to date
+    """
+    def __init__(self,
+                 tle_name="ISS (ZARYA)",
+                 tle_file="https://celestrak.com/NORAD/elements/stations.txt",
+                 tle_max_age=3600):
+        self._tle_name = tle_name
+        self._tle_file = tle_file
+        self._tle_max_age = tle_max_age
+        self._tle = None
+        self.reload()
+
+    def build_index(self, tle_lines):
+        index = {}
+        for i in range(0, len(tle_lines), 3):
+            index[tle_lines[i].strip()] = (tle_lines[i + 1], tle_lines[i + 2])
+        return index
+
+    def reload(self):
+        print("Loading: %s" % self._tle_file)
+
+        try:
+            ctx = ssl.create_default_context()
+            ctx.check_hostname = False
+            ctx.verify_mode = ssl.CERT_NONE
+            with urllib.request.urlopen(self._tle_file, context=ctx) as response:
+                tle_lines = response.read().decode("utf-8").splitlines()
+            index = self.build_index(tle_lines)
+            tle_data = index[self._tle_name]
+            self._tle = ephem.readtle(self._tle_name, tle_data[0], tle_data[1])
+        except Exception as e:
+            print(e)
+
+        self._tle_age = time.time()
+
+    @property
+    def tle(self):
+        return self._tle
+
+    @property
+    def tle_expired(self):
+        return time.time() - self._tle_age > self._tle_max_age
+
+
+iss = tle_reader(tle_name="ISS (ZARYA)", tle_max_age=5520)  # 92 minutes
+
+if iss.tle is None:
+    sys.exit(0)
+
+myloc = ephem.Observer()
+myloc.lon = LONGITUDE
+myloc.lat = LATITUDE
+myloc.elevation = ALTITUDE
+
+running = True
+
+while running:
+    myloc.date = time.strftime('%Y/%m/%d %H:%M:%S', time.gmtime())
+    iss.tle.compute(myloc)
+    alt = math.degrees(iss.tle.alt)
+    
+    if alt > 0:  # iss is flying over our location
+        fn = datetime.datetime.now().strftime(FILE_FMT)
+        f = open(fn, "wb")
+        proc = subprocess.Popen(rtl_cmd, stdout=f)
+        while alt > 0:
+            myloc.date = time.strftime('%Y/%m/%d %H:%M:%S', time.gmtime())
+            iss.tle.compute(myloc)
+            alt = math.degrees(iss.tle.alt)
+            time.sleep(10)
+        f.flush()
+        os.kill(proc.pid, signal.SIGTERM)
+        proc.wait()
+        f.close()
+    elif iss.tle_expired:
+        iss.reload()  # we could be running for days / weeks
+    else:
+        time.sleep(10)  # do nothing, wait for iss to arrive