ECG project. Building the right leg circuit. Help!

[czmark]

Hi all, im enrolled in biomedical engineering and in last year. Our year long project is to build and design our own ECG. So my group is in the early stages of building.

My question this week is with building of the Right leg circuit. We are using the AD620 because it complys with all AMII standards.

We are thinking of using a AD705J but dont know abouts hooking it up.

We also have to build a notch filter and thinking of using a UAF42 chip.

If anyone has any information or schematics to follow for me to help me get the ball rolling for this project it would be much appreciated.

 

[czmark]

I was wondering if this OP97 is a good chip to use ? I found this schematic on this here.

Thank you Mark

 

[audioguru]

The OP97 opamp will work perfectly in that circuit.

 

[czmark]

Thank you!

When looking at the notch filter to eliminate the 60hz noise the book shows 2, OPA2111BM.

Is there any better components that can be used for a notch filter?

 

[audioguru]

Thank you!

When looking at the notch filter to eliminate the 60hz noise the book shows 2, OPA2111BM.
Is there any better components that can be used for a notch filter?

I don't know which book you are talking about.
The circuit with "a right knee" uses shielded audio cables to the person and the right knee has common-mode signals fed to it with opposite phase for cancellation of the common-mode signals. The common-mode signals include DC changes produced by the person's muscles and 60Hz mains hum picked up by the person. A notch filter might not be needed.

 

[czmark]

so i built the exact circuit. i tried plugging a patient simulator using the schematic and all it shows is noise with or without the patient simulator.
also used as little and short cables as possible to reduce noise. what could be the issue ?

 

[audioguru]

Did you use shielded audio cables?

 

[czmark]

Alligator clips. Been in the lab now for a week trying to get some sort of signal out of this AD620 i even ditched the right legt circuit to try and get the signal working by just changing the gain by different resistance between pin 1 an 8 and inputing the LA and RA into the inputs of the ad620. Also tried putting a low pass and high pass after to see if the ecg was covered with noise but still couldn't get the signal.

Anyone have any other suggestions i should try or other schematics. I've search many schematics online and still no luck.

Thank

 

[audioguru]

Are the 220k input resistors connected very close to the circuit?
Do you have shielded audio cable from the 220k resistors to the sensor pads with the shields connected to 0V at the circuit and not connected to anything at the sensor pads?

Please explain the noise. Random hiss? Mains hum?