would like to develop a simple 3 lead ECG monitoring system using NI ELVIS hardware

[Joaana]

I would like to develop a simple 3 lead ECG monitoring system using NI ELVIS hardware.

I have  to measure lead configuration II and record the readings(samples) over 1 hour duration.

My project is related to time domain maesures of Heart Rate Variability for which i need long term readings.

 In short i need to accquire real time ECG samples but i am unable to get a good circitry.

Pleasse help me if possible and If you have developed this sort of a 3 lead monitoring system before please

email me. thanks

[Ali84]

Hello Joanna. I used a NI USB DAQ for acquisition when implementing my ECG, but the circuitry I used should be of help. Here's the reference,

It´s an articel in Scientific American, I used the INstrumentation amplifier mentioned there (AD624AD) and it worked fine. As for the  electrodes, I did have to buy disposable ones used in actual medical aplications (the quarters didn't work for me):

"Home is where the ECG Is"

Scientific American Magazine

By Shawn Carlson

Section: The Amateur Scientist

Page 86

If you can't get it, I have some scans that may help.

Cheers.

Ali

[Joaana]

hii Ali,

 Thanx for the help. Can u plz send the scans coz the site shows just one picture and its not clear. Actually i hav already built a basic ECG amplifier stage and it is sort of working with a gain of 700. But hav not yet tried it on the NI Elvis protyping board. I hav to  even try it on a human subject. I jus needed a better but simple circuit to try.

   Am attaching the model of my circuit. Can u tell me if it will work out?

[Ali84]

Hello again. I had a look at your circuit and the datasheet of the opamp you're using. When I first tried to implement my circuit, I also used an opamp (TL084), and used a configuration of an instrumentation amplifier (Microelectronic Circuits, Sedra/Smith). Nevertheless, there was too much noise interfering with the readings. I therefore had to buy the *more expensive* amplifier mentioned in the article. The LF411 you are working with is also an opamp, but not an instrumentation amplifier. Since you tell me you'd already got some readings, I suppose your circuit IS working, just make sure what you're getting are TRUE readings and not noise. I myself tried filtering the signal from the Opamp using a Sallen Key Low Pass Filter, but still didn't work.

Anyway, the circuit in the article is way simpler, though I suggest you try another filter than the passive one suggested there should you still have noise problems. What are you using as electrodes?