Play a file when radio carrier signal drops

gb3py_mon.py

#!/usr/bin/python

# Run this with RTL-SDR connected to Raspberry Pi and Pipe rtl_power to it as follows:
# rtl_power -f 433.175M:433.225M:0.005M -p 42 -g 20 -i 3 | python gb3py_mon.py
# Set the -p (Parts per million calibration) and -g (Gain) as required for your SDR. You may also need to change the threshold for detecting a carrier at line 27

import sys
import datetime
import os
do_run = True
is_qrv = False
is_qso = False
periods_qrv = 0
play_file_next = False
idents_since_file = 0

while do_run:
	i = ''
	line = ''
	while i != '\n':
		# Read a line from rtl_power
		i = sys.stdin.read(1)
		line += i
	if "," in line:
		currentDT = datetime.datetime.now()
		vals = line.split(",")
		# 433.200MHz is the 14th element in the array. 
		# A strength over -25dB is considered a carrier from the repeater
		if float(vals[14]) > -25:
			is_qrv = True
			periods_qrv += 1
			play_file_next = False # Ensures we don't double with a QSO
			print (currentDT.strftime("%H:%M:%S")) + " QRV for " + str(periods_qrv) + " periods"
			# rtl_power sends a line every 5 secs, so we consider a QSO in progress after 100 contiguous secs with a carrier
			if periods_qrv > 19:
				if is_qso == False:
					print (currentDT.strftime("%H:%M:%S")) + " Strength: " + vals[14]
					print (currentDT.strftime("%H:%M:%S")) + " *** NOW IN QSO ***"
				is_qso = True
				idents_since_file = 0
		else:
			# No carrier present 
			if is_qrv == True: # Carrier was there on the last sample
				# The period with a carrier lasted less than 20 seconds, so we assume it was a CW ident
				if periods_qrv <4:
					idents_since_file += 1
					print "Beacon number " + str(idents_since_file)
				if idents_since_file == 4:
					# If this is the 4th CW ident since we last played the wav file, set the wav file to play
					play_file_next = True
					idents_since_file = 0
			if is_qso == True: 
				# There was a carrier last sample and it was part of a QSO (>100 secs of carrier)
				periods_qrv = 0 # Reset the CW idents counter
				play_file_next = True # Play the file now the QSO is over
			if play_file_next == True:
				print (currentDT.strftime("%H:%M:%S")) + " *** QSO ENDED, playing WAV ***"
				# System call to play /home/pi/test.wav on the soundcard with ID 0 (you may need 1,0 for some USB soundcards)
				os.system("mplayer -ao alsa:device=hw=0,0 /home/pi/test.wav")
				play_file_next = False
			is_qrv = False
			is_qso = False
			periods_qrv = 0
		sys.stdout.flush() # Ensures any prints happen immediately