ECG circuit design

[mert]

u can use this circuit diagram.. i get nearly original ecg signal.

 

[Arouse1973]

As a PQRST responce that's not bad. The P and Q are a bit low and theT is too high. But very good.
Adam

 

[mert]

it is my ecg signal and it is not extremely good .device was tried on lots of people and there were different PQRST waveforms..

 

[(*steve*)]

And of course you optocoupled the signal to the scope, right?

It would be interesting to see if one of these could be designed using a quad op-amp package (using 3 to make an instrumentation amp).

 

[mert]

no i did not..
ad620 is an instrumentation amplifier so 741 is not for this work.. 741 uses for just increasing gain because ins. amp. gain is not enough to see all waveforms of PQRST..

 

[(*steve*)]

no i did not..

But I assume you know why I said that.

ad620 is an instrumentation amplifier so 741 is not for this work.. 741 uses for just increasing gain because ins. amp. gain is not enough to see all waveforms of PQRST..

True, but you can make an instrumentation amp from 3 op-amps. I was wondering if that could be dome well enough to make this circuit using just jellybean components.

 

[mert]

i couldnt do that just jellybean components because i had not special cables for human body. i used copper cable and -as u can guess- loss is too much if u wanna amplify 1mV.. may be it is possible but i tried to make ins. amp. with "jellybean" components and they could not sense signal.. if u can i wanna learn how it is done..

 

[Harald Kapp]

Stve has a valid point about decoupling the signal from the amplifier to the scope, e.g. by using an optocoupler. Since the amplifier is directly connected to a human body, you need to do everything possible to protect the human from a malfunction and possibly hazardous currents and/or voltages.

i used copper cable and -as u can guess- loss is too much

Could you explain this in more detail? The instrumentation amplifier draws a negligible input current (max. 4nA over the full temperature range). Therefore the losses in the cables leading to the human subject should be negligible, too (e.g. even at 100 Ohm the voltage drop will be <= 400nV, much less than the millivolts you expect to measure).

Here is one article about rolling your own instrumentation amplifier and here is some basic material on ins. amps.

 

[mert]

thanks for your interest and advices

 

[(*steve*)]

thanks for your interest and advices

You have no idea how well timed your thread was...

Thanks for the contribution

 

[(*steve*)]

As an interesting aside, here is a datasheet that describes the use of optocouplers for isolating linear signals.

It is interesting to note that there are two transistors, one of which is used in the feedback loop on the input side.

 

[mert]

You have no idea how well timed your thread was...

Thanks for the contribution

absolutely no idea why this thread is well timed?

 

[mert]

by the way, of course i should have do isolation circuit for this app. but i hadnt enough time and i had not facility to buy something for isolation circuit