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Need Assistance with design of ECG using AD623

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Evolve

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Hi,

I am working on designing an ECG using the AD623 Op Amp. So far I can input an ECG signal at 20mVPP into the AD 623 from a signal generator and produce a result (I know this is redundant I just wanted to see if it could actually work with low Voltages). When I connected the electrodes to my body and tried to recover a signal I couldn't see anything on the scope. So I used labview and filtered the signal using a low pass filter. I am only picking up a weird 60Hz signal and not my ECG. Any ideas and thought would be much appreciated.

Currently I am in the process of building a low pass filter to see if that will do anything but I have a hunch I am not actually picking up any ECG signal in the first place using my electrodes.
 
hi,
Not knowing your location, I suspect the local mains frequency is 60Hz.??

I expect you are using the AD623 as differential inputs from the pads and is the pad to AD623 wiring screened.?
 
I have a hunch I am not actually picking up any ECG signal in the first place using my electrodes.

The ECG signal is there but with 0.1~0.6mV pk-pk modulated heavily with 60Hz power supply line frequency.

Or should I say, more appropriately, healthy 60Hz signal modulated slightly with 0.1mV ECG signal.
 
Hi there,

You might pick up more signal if you connect the electrodes to the right place
on your body. Did you look into this at all? If i rem right one goes on your
foot.
 
Hi Everyone,

Thanks for the quick responses, I have been playing around with the instrumentation amplifier and managed to burn it thanks in part to a faulty breadboard not to worry the replacements are on their way. I am indeed accounting for 60Hz noise but I am using a bezzel low pass amplifier created using lab view. I am using the wrists as my 2-electrodes because that's my project I could easily use the LA and RL configuration but that wont work within my constrains. My theoretical reasoning has hit a wall though I have been looking at a lot of amatuer ECG circuits and everyone one of them has resistors in the inputs to the instrumentation Amp. ie. from electrode into resistor into inst. Amp input. Why is that? I am wondering if that has something to do with preventing saturation of the op amp. I plan on putting a 47K resistor there as well I would appreciate any thoughts on this.
 
Hi Everyone,
everyone one of them has resistors in the inputs to the instrumentation Amp. ie. from electrode into resistor into inst. Amp input. Why is that? I am wondering if that has something to do with preventing saturation of the op amp. I plan on putting a 47K resistor there as well I would appreciate any thoughts on this.

Consider you have long leads from the pads to the VERY high input impedance of the AD623 non-inv inputs.
Without the series 47K resistors you could get 'heavy' discharge currents flowing into these inputs, which could blow the AD623 inputs.

Use the 47K, they will have minimal effect on the pad signals.

BTW: I always try to use at least a 10K on NI to OPA's, when using external signal inputs to the NI.
 
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