Warning: This post is several years old and the author has marked it as poor quality (compared to more recent posts). It has been left intact for historical reasons, but but its content (and code) may be inaccurate or poorly written.

Here’s a schematic of the prime number calculator I’m working on. Last night I finished wiring all 12 shift registers for the primary display, so now it’s time to start working on software. Notice that we have a lot of pins free still. This will be advantageous if I decide to go crazy adding extraneous functionality, such as fancy displays (LCD?, 7-segment LEDs?, VFD?, all 3?!) or creative input systems (how about a numerical keypad?).


After feeling the stink of paying almost $15 for 100′ of yellow, 24 gauge, solid-core wire from DigiKey I was relieved (and a little embarrassed) to find I could score 1,000′ of yellow, 24 gauge, threaded wire for $10 at Skycraft! Anyway, here’s the current schematic:

Last weekend was field day, a disaster simulation / competition for amateur radio operators. In a sentence, people are encouraged to make as many contacts as they can around the world (earning points) using emergency radio preparations (battery and solar powered radios, temporary antennas, etc) for a full 24 hours (2pm to 2pm). I spent the time with the UCF Amateur Radio Club who set up big antennas in a grassy field on campus. It was a fun experience, and the first time I ever got to see a HF rig in operation. A representative for the UCF newspaper showed up, took some interviews, and I ended-up being quoted in the article. I can also be seen in the photo, if you look close enough (yellow square).


Being that amateur radio was something I got into independently (I didn’t know anyone else with a license) I was (and still am) very isolated in the hobby. I’m really thankful I found the UCF ARC, even though it wasn’t until I’d already been going to UCF for 2 years and was already on my way out. Seeing (and actually get to use) a HF rig was an eye-opening experience for me, and one I’m a little regretful I participated in. Before yesterday, I had already come to terms with my situation (going to dental school in a few weeks and virtually dropping all of my hobbies) and was content with my summer accomplishments so far. My summer goal was to get into radio, and before yesterday I felt I had. I studied for my exam, got my license, learned how to use repeaters on VHF to easily make local contacts, and I was satisfied. I knew HF was out there, and that it allowed communication over thousands of miles, but I ignored it knowing I wouldn’t get into it this summer (the equipment is just too expensive for me to justify purchasing). Now, after sitting in front of a rig for several hours, I wish I had the time to upgrade my license, earn a little cash to blow on a HF radio, and spend a few weeks sitting in front of it scouring the waves for random voices around the world. I know it’s a little morbid, but I’d probably have to compare the feeling I’m experiencing with what an old person feels like when they realize their end is near and that they won’t be able to do the things they always dreamed they would. Oh well, at least I’ll be able to fill holes in teeth soon. [smiles convincingly]


After the tents, antennas, and radios were mostly set up, everyone was exhausted. I was ready to make some contacts! I fired-up my ‘ol netbook and tried communicating over 40m using psk (a digital mode), a mode I’ve never used, with software I’ve never used, on a band I’ve never used. It wasn’t working either. I spent the first several hours in frustration because what I was trying to do wasn’t working, and I couldn’t figure out why. This photo was taken at the height of my frustration.

Bitwise programming techniques (manipulating the 1s and 0s of binary numbers) are simple, but hard to¬† remember if you don’t use them often. Recently I’ve needed to perform a lot of bitwise operations. If I’m storing true/false (1-bit) information in variables, it’s a waste of memory to assign a whole variable to the task (the smallest variable in C is a char, and it contains 8 bits). When cramming multiple values into individual variables, it’s nice to know how to manipulate each bit of a variable.

y = (x >> n) & 1; // stores nth bit of x in y.  y becomes 0 or 1.

x &= ~(1 << n); // forces nth bit of x to be 0.  all other bits left alone.

x &= (1 << (n + 1)) - 1; // leaves lowest n bits of x; all higher bits set to 0.

x |= (1 << n); // forces nth bit of x to be 1.  all other bits left alone.

x ^= (1 << n); // toggles nth bit of x.  all other bits left alone.

x = ~x; // toggles ALL the bits in x.

Warning: This post is several years old and the author has marked it as poor quality (compared to more recent posts). It has been left intact for historical reasons, but but its content (and code) may be inaccurate or poorly written.

Update: this project is now on GitHub https://github.com/FredEckert/pySquelch

I’ve been working on the pySquelch project which is basically a method to graph frequency usage with respect to time. The code I’m sharing below listens to the microphone jack on the sound card (hooked up to a radio) and determines when transmissions begin and end. I ran the code below for 24 hours and this is the result:


This graph represents frequency activity with respect to time. The semi-transparent gray line represents the raw frequency usage in fractional minutes the frequency was tied-up by transmissions. The solid blue line represents the same data but smoothed by 10 minutes (in both directions) by the Gaussian smoothing method modified slightly from my linear data smoothing with Python page.


I used the code below to generate the log, and the code further below to create the graph from the log file. Assuming your microphone is enabled and everything else is working, this software will require you to determine your own threshold for talking vs. no talking. Read the code and you’ll figure out how test your sound card settings.

If you want to try this yourself you need a Linux system (a Windows system version could be created simply by replacing getVolEach() with a Windows-based audio level detection system) with Python and the alsaaudio, numpy, and matplotlib libraries. Try running the code on your own, and if it doesn’t recognize a library “aptitude search” for it. Everything you need can be installed from packages in the common repository.

import time, random, alsaaudio, audioop
inp = alsaaudio.PCM(alsaaudio.PCM_CAPTURE,alsaaudio.PCM_NONBLOCK)


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.
	while True:
		if a==b==c:
			if testLevel: print "RESULT:",a
	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:

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

while True:

The logging code (above) produces a log file like this (below). The values represent the start time of each transmission (in seconds since epoch) followed by the duration of the transmission.

1245300044,5 1245300057,4 1245300063,16 1245300094,13 1245300113,4 1245300120,14 1245300195,4 1245300295,4 1245300348,4 1245300697,7 1245300924,3 1245301157,4 1245301207,12 1245301563,4 1245302104,6 1245302114,6 1245302192,3 1245302349,4 1245302820,4 1245304812,13 1245308364,10 1245308413,14 1245312008,14 1245313953,11 1245314008,6 1245314584,4 1245314641,3 1245315212,5 1245315504,6 1245315604,13 1245315852,3 1245316255,6 1245316480,5 1245316803,3 1245316839,6 1245316848,11 1245316867,5 1245316875,12 1245316893,13 1245316912,59 1245316974,12 1245316988,21 1245317011,17 1245317044,10 1245317060,6 1245317071,7 1245317098,33 1245317140,96 1245317241,15 1245317259,14 1245317277,8 1245317298,18 1245317322,103 1245317435,40 1245317488,18 1245317508,34 1245317560,92 1245317658,29 1245317697,55 1245317755,33 1245317812,5 1245317818,7 1245317841,9 1245317865,25 1245317892,79 1245317972,30 1245318007,8 1245318021,60 1245318083,28 1245318114,23 1245318140,25 1245318167,341 1245318512,154 1245318670,160 1245318834,22 1245318859,9 1245318870,162 1245319042,57 1245319102,19 1245319123,30 1245319154,18 1245319206,5 1245319214,13 1245319229,6 1245319238,6 1245319331,9 1245319341,50 1245319397,71 1245319470,25 1245319497,40 1245319540,8 1245319551,77 1245319629,4 1245319638,36 1245319677,158 1245319837,25 1245319865,40 1245319907,33 1245319948,92 1245320043,26 1245320100,9 1245320111,34 1245320146,8 1245320159,6 1245320167,8 1245320181,12 1245320195,15 1245320212,14 1245320238,18 1245320263,46 1245320310,9 1245320326,22 1245320352,27 1245320381,15 1245320398,24 1245320425,57 1245320483,16 1245320501,40 1245320543,43 1245320589,65 1245320657,63 1245320722,129 1245320853,33 1245320889,50 1245320940,1485 1245322801,7 1245322809,103 1245322923,5 1245322929,66 1245323553,4 1245324203,15 1245324383,5 1245324570,7 1245324835,4 1245325200,8 1245325463,5 1245326414,12 1245327340,12 1245327836,4 1245327973,4 1245330006,12 1245331244,11 1245331938,11 1245332180,5 1245332187,81 1245332573,5 1245333609,12 1245334447,10 1245334924,9 1245334945,4 1245334971,4 1245335031,9 1245335076,11 1245335948,16 1245335965,27 1245335993,113 1245336107,79 1245336187,64 1245336253,37 1245336431,4 1245336588,5 1245336759,7 1245337048,3 1245337206,13 1245337228,4 1245337309,4 1245337486,6 1245337536,8 1245337565,38 1245337608,100 1245337713,25 1245337755,169 1245337930,8 1245337941,20 1245337967,6 1245337978,7 1245337996,20 1245338019,38 1245338060,127 1245338192,30 1245338227,22 1245338250,15 1245338272,15 1245338310,3 1245338508,4 1245338990,5 1245339136,5 1245339489,8 1245339765,4 1245340220,5 1245340233,6 1245340266,10 1245340278,22 1245340307,7 1245340315,28 1245340359,32 1245340395,4 1245340403,41 1245340446,46 1245340494,58 1245340554,17 1245340573,21 1245340599,3 1245340604,5 1245340611,46 1245340661,26 1245340747,4 1245340814,14 1245341043,4 1245341104,4 1245341672,4 1245341896,5 1245341906,3 1245342301,3 1245342649,6 1245342884,5 1245342929,4 1245343314,6 1245343324,10 1245343335,16 1245343353,39 1245343394,43 1245343439,62 1245343561,3 1245343790,4 1245344115,3 1245344189,5 1245344233,4 1245344241,6 1245344408,12 1245344829,3 1245345090,5 1245345457,5 1245345689,4 1245346086,3 1245347112,12 1245348006,14 1245348261,10 1245348873,4 1245348892,3 1245350303,11 1245350355,4 1245350766,5 1245350931,3 1245351605,14 1245351673,55 1245351729,23 1245351754,5 1245352123,37 1245352163,21 1245352186,18 1245352209,40 1245352251,49 1245352305,8 1245352315,5 1245352321,6 1245352329,22 1245352353,48 1245352404,77 1245352483,58 1245352543,17 1245352570,19 1245352635,5 1245352879,3 1245352899,5 1245352954,4 1245352962,6 1245352970,58 1245353031,21 1245353055,14 1245353071,52 1245353131,37 1245353170,201 1245353373,56 1245353431,18 1245353454,47 1245353502,13 1245353519,106 1245353627,10 1245353647,12 1245353660,30 1245353699,42 1245353746,28 1245353776,29 1245353806,9 1245353818,21 1245353841,10 1245353853,6 1245353862,224 1245354226,4 1245354964,63 1245355029,4 1245355036,142 1245355180,148 1245355330,7 1245355338,23 1245355363,9 1245355374,60 1245355437,142 1245355581,27 1245355609,5 1245355615,2 1245355630,64 1245355700,7 1245355709,73 1245355785,45 1245355834,85 1245355925,9 1245356234,5 1245356620,6 1245356629,12 1245356643,29 1245356676,120 1245356798,126 1245356937,62 1245357001,195 1245357210,17 1245357237,15 1245357258,24 1245357284,53 1245357339,2 1245357345,27 1245357374,76 1245357452,28 1245357482,42 1245357529,14 1245357545,35 1245357582,74 1245357661,30 1245357693,19 1245357714,38 1245357758,11 1245357777,37 1245357817,49 1245357868,19 1245357891,31 1245357931,48 1245357990,49 1245358043,24 1245358082,22 1245358108,17 1245358148,18 1245358168,7 1245358179,6 1245358186,19 1245358209,17 1245358229,5 1245358240,9 1245358252,10 1245358263,6 1245358272,9 1245358296,26 1245358328,49 1245358381,6 1245358389,38 1245358453,19 1245358476,24 1245358504,21 1245358533,76 1245358628,24 1245358653,10 1245358669,105 1245358781,20 1245358808,14 1245358836,6 1245358871,61 1245358933,0 1245358936,44 1245358982,11 1245358996,25 1245359023,15 1245359040,32 1245359076,19 1245359099,13 1245359117,16 1245359138,12 1245359161,33 1245359215,32 1245359249,14 1245359272,7 1245359314,10 1245359333,36 1245359371,21 1245359424,10 1245359447,61 1245359514,32 1245359560,42 1245359604,87 1245359700,60 1245359762,23 1245359786,4 1245359791,8 1245359803,6 1245359813,107 1245359922,29 1245359953,22 1245359978,86 1245360069,75 1245360147,22 1245360170,0 1245360184,41 1245360239,15 1245360256,34 1245360301,37 1245360339,1 1245360342,28 1245360372,20 1245360394,32 1245360440,24 1245360526,3 1245360728,3 1245361011,4 1245361026,35 1245361064,137 1245361359,5 1245362172,11 1245362225,21 1245362248,51 1245362302,20 1245362334,42 1245362418,12 1245362468,7 1245362557,9 1245362817,3 1245363175,4 1245363271,4 1245363446,3 1245363539,4 1245363573,4 1245363635,1 1245363637,3 1245363740,5 1245363875,3 1245364075,4 1245364354,14 1245364370,19 1245364391,49 1245364442,34 1245364478,23 1245364502,80 1245364633,15 1245364650,8 1245364673,16 1245364691,47 1245364739,53 1245364795,39 1245364836,25 1245365353,4 1245365640,11 1245365665,5 1245365726,8 1245365778,7 1245365982,4 1245366017,13 1245366042,6 1245366487,4 1245366493,4 1245366500,4 1245366507,3 1245366622,5 1245366690,5 1245366946,4 1245366953,16 1245366975,8 1245366996,7 1245367005,7 1245367031,6 1245367040,9 1245367051,7 1245367059,23 1245367084,76 1245367166,158 1245367740,4 1245367804,3 1245367847,4 1245367887,9 1245369300,10 1245369611,12 1245370038,10 1245370374,8 1245370668,5 1245370883,5 1245370927,7 1245370945,9 1245370961,16 1245370978,414 1245371398,135 1245371535,252 1245371791,238 1245372034,199 1245372621,4 1245372890,5 1245373043,7 1245373060,9 1245373073,6 1245373081,68 1245373151,10 1245373162,49 1245373212,79 1245373300,12 1245373313,38 1245373353,20 1245373374,59 1245373435,28 1245373465,94 1245373560,11 1245373574,53 1245373629,22 1245373654,6 1245373662,334 1245373998,169 1245374176,41 1245374219,26 1245374246,51 1245374299,31 1245374332,57 1245374391,55 1245374535,4 1245374759,7 1245374769,200 1245374971,215 1245375188,181 1245375371,81 1245375455,59 1245375516,33 1245375552,19 1245375572,56 1245375629,220 1245375850,32 1245375884,26 1245375948,7 1245375964,114 1245376473,4 1245376810,13 1245378296,10 1245378950,12 1245379004,3 1245379569,4 1245379582,4 1245379615,6 1245380030,3 1245380211,4 1245380412,14 1245380727,4 1245380850,4 

This log file is only 7.3 KB. At this rate, a years’ worth of log data can be stored in less than 3MB of plain text files. The data presented here can be graphed (producing the image at the top of the page) using the following code:

print "loading libraries...",
import pylab, datetime, numpy
print "complete"

def loadData(fname="log.txt"):
	print "loading data...",
	# load signal/duration from log file
	raw=raw.replace('n',' ')
	raw=raw.split(" ")
	for line in raw:
		if len(line)<3: continue
	print "complete"
	return signals

def findDays(signals):
	# determine which days are in the log file
	print "finding days...",
	for signal in signals:
		day = signal[0].date()
		if not day in days:
	print "complete"
	return days

def genMins(day):
	# generate an array for every minute in a certain day
	print "generating bins...",
	for i in xrange(60*60):
	print "complete"
	return mins

def fillMins(mins,signals):
	print "filling bins...",
	for signal in signals:
		if not signal[0].date() == dayToDo: continue
		prebuf = sec.second
		if dur+prebuf<60: # simple case, no rollover seconds
		else: # if duration exceeds the minute the signal started in
			while (dur>0): # add rollover seconds to subsequent minutes
				if dur< =0: break
				if dur>=60: vals[minOfDay]=60
				else: vals[minOfDay]=dur
	print "complete"
	return vals

def normalize(vals):
	print "normalizing data...",
	for i in xrange(len(vals)):
	print "complete"
	return vals

def smoothListGaussian(list,degree=10):
	print "smoothing...",
	for i in range(window):
	for i in range(len(smoothed)):
	while len(list)>len(smoothed)+int(window/2):
	while len(list)>len(smoothed):
	print "complete"
	return smoothed

for day in days:
	pylab.title("147.120 MHz Usage for "+str(day))
	pylab.xlabel("time of day")
	pylab.ylabel("fractional usage")

This morning I woke up at 4:45am, hopped out of bed, and raced to the university parking lot for field day. It’s pretty much a flea market with an emphasis in ham radio and associated electronics. This is a panorama of the parking lot the tailgate was held in, taken from the roof of a parking garage at about 9am. The UCF ARC (the amateur radio club which sponsored the event) is stationed under the white tent.

My goal was to purchase a [working] oscilloscope, and I lucked-out. I ended-up purchasing two, and I’m glad I did! The 1st one (the one with the green circular screen) crapped-out on me after literally 1 minute. (By crapped-out I mean it started spurring thick gray smoke and made my whole apartment smell like a burned marshmallow). At $5, I’m not crying over it. The second one is a 1969 Tektronix 561A 10 MHz oscilloscope. Just think, these things just started started being produced the same year Neil Armstrong walked on the moon. I tested it and it seems to be functioning well. At $10, I’m very happy!

Here you can see it attached to my prime number generator described in agonizingly-boring detail over the last several weeks’ posts. It’s attached to one of the microcontroller pins responsible for multiplexing the LED display. Finally, a way to assess high speed power output as a function of time. The output of the microcontroller isn’t performing like I expected, and since it’s a series of pulses I can’t use a volt meter to measure its output. Thus, the need [more like desire] for an oscilloscope.

Warning: This post is several years old and the author has marked it as poor quality (compared to more recent posts). It has been left intact for historical reasons, but but its content (and code) may be inaccurate or poorly written.

I’m often drawn toward projects involving data analysis with Python. When I found out a fellow ham in Orlando was using his computer to stream a popular local repeater frequency over the internet I got excited because of the potential for generating data from the setup. Since this guy already has his radio connected to his PC’s microphone jack, I figured I could write a Python app to check the microphone input to determine if anyone is using the frequency. By recording when people start and stop talking, I can create a log of frequency activity. Later I can write software to visualize this data. I’ll talk about that in a later post. For now, here’s how I used Python and a Linux box (Ubuntu, with the python-alsaaudio package installed) to generate such logs.

We can visualize this data using some more simple Python code. Long term it would be useful to visualize frequency activity similarly to how I graphed computer usage at work over the last year but for now since I don’t have any large amount of data to work with. I’ll just write cote to visualize a QSO (conversation) with respect to time. It should be self-explanatory. This data came from data points displayed in the video (provided at the end of this post too).


And, of course, the code I used to generate the log files (seen running in video above): Briefly, this program checks the microphone many times every second to determine if its state has changed (talking/no talking) and records this data in a text file (which it updates every 10 seconds). Matplotlib can EASILY be used to graph data from such a text file.

import alsaaudio, time, audioop, datetime
inp = alsaaudio.PCM(alsaaudio.PCM_CAPTURE,alsaaudio.PCM_NONBLOCK)

squelch = False
lastLog = 0
dataToLog = ""

def logIt(nowSquelch):
 global dataToLog, lastLog
 timeNow = datetime.datetime.now()
 epoch = time.mktime(timeNow.timetuple())
 if nowSquelch==True: nowSquelch=1
 else: nowSquelch=0
 logLine="%s %dn"%(timeNow, nowSquelch)
 print timeNow, nowSquelch
 if epoch-lastLog>10:
 #print "LOGGING..."
 lastLog = epoch

while True:
 l,data = inp.read()
 if l:
 vol = audioop.max(data,2)
 if vol>800: nowSquelch = True
 else: nowSquelch = False
 if not nowSquelch == squelch:
 squelch = nowSquelch

To use this code make sure that you’ve properly calibrated it. See the “vol>800” line? That means that if the volume in the microphone is at least 800, it’s counted as talking, and less than it’s silence. Hopefully you can find a value that counts as silence when the squelch is active, but as talking when the squelch is broken (even if there’s silence). This is probably best achieved with the radio outputting at maximum volume. You’ll have to run the program live with that line un-commented to view the data values live. Find which values occur for squelch on/off, and pick your threshold accordingly.

After that you can visualize the data with the following code. Note that this is SEVERELY LIMITED and is only useful when graphing a few minutes of data. I don’t have hours/days of data to work with right now, so I won’t bother writing code to graph it. This code produced the graph seen earlier in this page. Make sure matplotlib is installed on your box.

import pylab

def loadData():
 #returns Xs
 import time, datetime, pylab
 for line in raw:
 if len(line)<10: continue
 line = line.strip('n').split(" ")
 t=line[0]+" "+line[1]
 thisDay=time.strptime(t[0], "%Y-%m-%d %H:%M:%S")
 if timeStart==None: timeStart=e
 if line[-1]==1: stat=True
 else: stat=False
 if not lastOn and line[-1]=="1":
 return onTimes

times = loadData()
for t in times:
pylab.title("A little QSO")
pylab.xlabel("Time (minutes)")

Warning: This post is several years old and the author has marked it as poor quality (compared to more recent posts). It has been left intact for historical reasons, but but its content (and code) may be inaccurate or poorly written.

Now that I’ve worked-out the software side of the microcontroller-powered prime number generator, it’s time to start working on the hardware. I want to make a prototype which is far smaller and simpler than the final version but lets me practice driving lots of LEDs (30). I expect the final version to have around 80. Also, the heart of this project is an ATTiny2313 microcontroller, and for the full version I’d like to use an ATMEega8. I picked up an unfinished wooden box with a magnetic latch from Michaels. It’s delicate and tends to chip when you drill it, but moving slowly I’m able to make nice evenly-spaced holes.

This is the circuit concept. The chip is an ATTiny2313, sourced with 5V, where the left pins control the columns (by providing current) and the right pins control the rows (by providing ground). The “holes” at the top of the circuit represent where I hook up my PC and external power for testing purposes.

Thoughts from Future Scott (10 years later, August, 2019)

A+ for enthusiasm and construction but your design is… just no!

Why are you using an external crystal?

The schematic for the crystal is wrong: those capacitors should be to ground not in series!

You made the circuit diagram in InkScape!

You shouldn’t drive current directly out of the microcontroller pins.

The majority of the microcontroller CPU cycles will go into managing multiplexing of the display (not calculating primes).

After a little more work I have a functional device and it looks better than I expected. There are a few more features I want to add, and I want to work on the code some more, but I hope to be done tomorrow. The coolest part is that I’ve included an internal button which drives a pause/resume and speed-controller menu based upon the length of button presses! There’s a lot of awesome stuff I want to write, but once again, I’ll save it for the completed project page.

I rendered the cover sticker wrong and all the LEDs are mislabled. The first LED should be 2^0 (1), and the second should be 2^1 (2), etc. Also, 2^22 and 2^23 are mislabeled – oops! But the thing really does generate, differentiate, and display [only[ prime numbers. Once again, videos (including demonstration of the menus and the programming options) and source code will be posted soon.