The great Slashdot effect


First, let me thank everyone who came to visit my web page.  Even though it caused the dreaded Slashdot effect, I appreciate the interest.

Second, let me apologize for the Slashdot effect.   Both to the University of Utah and all the people coming to see my web page.  I underestimated the effect Slashdot users have on servers.  A 100Mb/s bandwidth is not enough to sustain all you great users.  Although I do not know the exact bandwidth we have, I have on occasion downloaded large files off the U's server at near 100Mb/s.  (Locally, on site, but it still had to go through the web server).  My guess is that it was really the server that got bogged down and not the bandwidth.  

Now that I have admitted my stupidity, I need to thank everyone who has sent me emails.  I have paraphrased some of the emails I thought were the most interesting.  I apologize if I did not list yours.  This does not mean I thought your email was stupid, but it either was asked by someone else or didn't think others would benefit as much with it.


The negative peak on your waveform looks normal.  A real industrial EKG uses 12 leads I think, one on each arm, one on each leg, and then a stripe across the chest and a few for extra good measure.  Depending on where you attach the electrodes you'll see different waveforms.

Thanks to all that responded about my negative spike.  I'm a little disappointed that I'm not a mutant, but I guess there's always Batman.
Also, some have suggested some good web sites on how to read ECGs.  Here's a few.

Oh, and I just loved this picture.  I've always been bad at drawing things on the computer, but this guy took the time to draw pretty pictures to try and explain the stuff to me.  Thanks!

Your waveform is screwed up.  P-wave is missing (ie. peak #1 on the example graph).  The T wave is ugly (peak #3)....

Yep, you're right!  This is an ugly waveform.  Part of it is due to electrode placement, and part is due to the interface with the sound card.  I have tried moving the electrodes around and can make the P-wave appear, so my choice during this test was poor.  As for the sound card interface, some of the ugliness went away with my signal processing, however, I didn't include it because everyone's sound card is different and trying to calibrate the math to remove the artifacts are not easy.  If those reasons aren't why my waveform is screwed up, then I guess I'm more of a mutant that I thought.  :)

Try putting two diodes in opposite directions across any two electrodes.

   Great idea!  The more protection, the better.

How about making an EEG (brain wave monitor)?

That would probably be the next thing I work on.  However, I am not sure how easy it would be.  One thing that would make it even cooler is to see if I can use the EEG to control my computer.  :)

KY Jelly makes a great electrode gel. 

Unfortunately, I don't have any of that stuff around, but I'm glad to know it's the same stuff they use on the real electrodes.  One question though: does it leave my chest smooth and touchable like lotion?  :)

You may get better results, and have to use slightly less lotion, by using pennies dated prior to 1982.  Why's this, you ask?  In 1982 the US Mint changed the compostition of the cent.  They started using copper-plated zinc about half-way through the year. Cents dated 1947 - 1981 are 90% copper and 10% zinc.  Cents from before WWII are bronze (various mixes of copper, nickel, and tin. They changed they alloy a few times).  So by using pre-1982 cents, you ought to get better conductivity.

Cool facts.  Do you tend to win all of the trivia games?

Isolate!  Isolate!  Isolate!  You need better electrical isolation!

Yes I do.  In my experiment, I was 99.9999% confident on my safety.  There are no other grounding places within 3 feet of me.  My power supply is electrically isolated.  My house is properly grounded.  The only way that I could create a ground loop is for someone to walk by and touch a 120V line to me.  In which case, I have bigger things on my mind (someone trying to kill me).  Everyone else has a different situation, so PLEASE BE CAREFUL!

For even better safety, consider using an optoisolator, a laptop, or some other means to isolate the 9V source with the computer.

It's been done.  Ramsey Electronics/Scientific American made the same system.

:(  Oh well, I guess I'll just have to be the first man to walk on Mars.

Connect the ECG to a portable cassette recorder.  Then you can record the waveform for later playback.

I love this idea!  Then you get isolation as well as recording capabilities.  You can technically record via the Windows sound recorder, but that takes a ton of disk space.  Yes, you can buy 40GB hard drives for $30 these days, but still......... electrical isolation!

Try doing ___________ to get the lower frequencies.

You guys come up with the best ideas.  I've heard about chopping the signal so that it's interlaced with around 1000Hz.  I've heard to use an intermediate frequency carrier like the way FM works.  I've heard to use an ADC to get the waveform out.  All very good!

Can I use a different op-amp to build this project?

Yep!  But you may need to look at the specifications before you do.  If you go to Radio Shack, I suggest you get the LM324.  It's a quad op-amp and supposedly low power.  Some things to look for is the range of the output (how much of the VDD supply can it operate out of), the input impedance (make sure it has 10^7 or higher), and has low enough noise (50nV/Hz^.5 or lower). 

Someone also informed me I neglected to consider the noise factor.  I used a JFET op-amp which has flicker (1/f) noise.  They were right.  I didn't even think about it.  Basically, 1/f noise is noise that gets worse with lower frequencies.  Since we're dealing with small signals and low frequencies, this noise is significant.  Luckily, I didn't have noise issues because it's low enough, but a better design would use another op-amp such as the LM324.  It has lower power, it's cheaper, it comes with 4 op-amps....I'm beginning to wonder why I chose the LF353. 

 You should try to put the electrodes on your arms, and left leg.  Then you'll get a more "standard" ECG.

I have tried putting the electrodes on both arms and the ground on my leg.  Unfortunately, it didn't get rid of the negative peak.  However, some one else said they have put them on both arms and they also get a negative peak.  So at least I'm not the only freak out there.  :)

Have you tried using a real ECG or read the ECG of someone else?

Not yet.  One of these days I'm going to have to bring a laptop to the local hospital and show off my ECG.  If it's not a busy day, some of the nurses and doctors may get a kick out of my device.  They may even let me compare my waveform with a real ECG. 

Also a great way to meet a cute doctor/nurse.  (It's not only the girls who want to meet a cute doctor).  If this turns out to be a great way to meet a cute (I'll be politically correct) person.  I'll post the results at slashdot.  ;)  Forget the slashdot effect!  Us geeks need to find ways to meet girls!

You loser.  You didn't expect the slashdot effect?

Sorry again.  I'm an idiot.