Hello Forum !!!

I have just joined the forum and i feel i wont waste anything here. I am really Exited. OK, to get to the point, I am in a project which is my senior project, and i will be making a wireless ECG (Electrocardiogram). I know this has been done but we aim to work on to improve on it and so on.

I tried to start with the first step of getting an analogue output from 2 electrodes, using an instrumentation amplifier with gain around 500. We just connected the 2 electrodes and simply wanted to see if we got anything on the Oscilloscope. I have tried a lot but it seems we r not doing something right. I wanted to know if there r some suggestions, to simply obtain an ECG signal or at least something resembling.

Waiting for any help

Thanks all,
Faisal

 

http://forum.allaboutcircuits.com/showthread.php?t=34443&highlight=ekg

Here is a link to a thread about your subject. It shows the opamps use and other important steps.

There is more info about EKG/ECG here. Use the search function for the forums and search for EKG and ECG.

 

Hello guys,

The wires connected to the electrodes are shielded as shown in figure 10 of this data-sheet. May i know what is the significance of this shielding ??

Thanks,
Faisal

 

The shielding is to keep stray signals from interfering with the signal you want to read.

 

I have another question. We r currently using 2 electrodes on the left and right arms. This is giving us a signal, but with some noise. If we have another electrode acting like a reference, the waveform gets smoother.

My quesiton is how can i juse use 2 main electrodes and get a smooth signal without using the 3rd reference electrode.

Another question is regarding filtering. Since we have to use both low and high pass filters, what is the frequency that would give us a proper signal. For, e.g if i have a bandpass filter with ranges 0-100 Hz, would that serve the purpose ??

Thanks for the help,
Faisal

 

Can you post your schematics?

 

The circuit is very similar to the one in this link:

http://www.nbb.cornell.edu/neurobio/land/PROJECTS/preamp2/index.html

We do have some capacitors for filtering, etc.

We also have a DC restoration stage at the output of the Instrumentation amplifier.

Now, the only thing is that we r trying to get rid of the 3rd electrode, which is held in one hand and its other end is grounded.

 

Have you asked yourself:


"Self, What frequencies are important to ECG monitoring?"

Once that has been answered, you can start choosing which filters you want/need.

And yes, a schematic would be nice.

 

Sigh! You have to post your schematics if you want any any discussion around your circuit. And for the filtering. We apply filtering in order to block unwanted signal. As an example a .5 Hz highpass filter may remove something called baseline wandering. The ECG complex has a certain bandwidth. So filtering may be useful to block signal outside this bandwidth, hence these signals will not give any useful information.
I will also recommend that you read up on this topic, as it will help you in this project. Try Google books http://books.google.com/ and search for "ecg amplifier"

 

The datasheets for many instrumentation amp ICs like the AD620A show a detailed ECG circuit that feeds an AC and DC signal out-of-phase to the patient's right leg to cancel common mode interference. The text for the circuits discuss frequencies.