While working to improve the python-based frequency activity logger I wrote a couple of entries back, I greatly increased its accuracy. I won’t go into the details other than saying that it simply polls the sound card a few times a second to listen for when a transmission begins and ends. The new data file format appears like this…

1245316480,5
1245316803,3
1245316839,6
1245316848,11
1245316867,5
1245316875,12
1245316893,13

The major change is that the date and time is recorded as seconds since epoch (Unix time) and the duration of the transmission is given after the comma. This greatly simplifies post-processing. Here is the revised python code to poll the sound card and generate such a log file:

##################################
##### UPDATED CODE IS IN A NEWER ENTRY #####
### CHECK THE PYTHON AND RADIO CATEGORIES ###
##################################
import time, random, alsaaudio, audioop
inp = alsaaudio.PCM(alsaaudio.PCM_CAPTURE,alsaaudio.PCM_NONBLOCK)
inp.setchannels(2)
inp.setrate(1000)
inp.setformat(alsaaudio.PCM_FORMAT_S8)
inp.setperiodsize(100)
addToLog=""
lastLogTime=0

testLevel=False ### SET THIS TO TRUE TO TEST YOUR SOUNDCARD

def getVolEach():
        # this is a quick way to detect activity.
        # modify this function to use alternate methods of detection.
	while True:
		l,data = inp.read() # poll the audio device
		if l>0: break
	vol = audioop.max(data,1) # get the maximum amplitude
	if testLevel: print vol
	if vol>10: return True ### SET THIS NUMBER TO SUIT YOUR NEEDS ###
	return False

def getVol():
        # reliably detect activity by getting 3 consistant readings.
	a,b,c=True,False,False
	while True:
		a=getVolEach()
		b=getVolEach()
		c=getVolEach()
		if a==b==c:
			if testLevel: print "RESULT:",a
			break
	if a==True: time.sleep(1)
	return a

def updateLog():
        # open the log file, append the new data, and save it again.
	global addToLog,lastLogTime
	#print "UPDATING LOG"
	if len(addToLog)>0:
        	f=open('log.txt','a')
        	f.write(addToLog)
        	f.close()
        	addToLog=""
	lastLogTime=time.mktime(time.localtime())

def findSquelch():
        # this will record a single transmission and store its data.
	global addToLog
	while True: # loop until we hear talking
		time.sleep(.5)
		if getVol()==True:
			start=time.mktime(time.localtime())
			print start,
			break
	while True: # loop until talking stops
		time.sleep(.1)
		if getVol()==False:
			length=time.mktime(time.localtime())-start
			print length
			break
	newLine="%d,%d\n"%(start,length)
	addToLog+=newLine
	if start-lastLogTime>30: updateLog() # update the log

while True:
	findSquelch()

To test the functionality of the code visually, you can use this quick and dirty method of graphing the log files output by this program. Keep in mind THIS IS NOT INTENDED TO BE USED other than to simply test the program.

##################################
##### UPDATED CODE IS IN A NEWER ENTRY #####
### CHECK THE PYTHON AND RADIO CATEGORIES ###
##################################
import pylab
import time, datetime
f=open('log.txt')
raw=f.read()
f.close()
raw=raw.split("\n")
pylab.figure()
for line in raw:
        if len(line)<5:continue
        line=line.split(",")
        sec=datetime.datetime.fromtimestamp(int(line[0]))
        dur=int(line[1])
        sec2=datetime.datetime.fromtimestamp(int(line[0])+int(line[1]))
        pylab.fill([sec,sec,sec2,sec2],[0,1,1,0],'k',lw=0,alpha=.5)
pylab.show()