ECG Circuit

[kiwan]

Hi

I have been trying to build this circuit but i have a few problems ...so any help is grateful

I am using battery to power the circuit ...two 9 v batteries in series but connected to ground

I am confused as i dont understand VSS and VDD.....as in what is the difference and how can i appply it..

also when you look at the circuit most of the +- 9V VSS VDD are connected to ground

abit confusing

I am just a hobbyist any help or knowledge would be helpful ....

http://www.cisl.columbia.edu/kinget_group/student_projects/ECG Report/E6001 ECG final report.htm


that is a link to the project i am building ....

I am getting the ECG signal butt when i connect my right leg to ground i lose the signal....


:-/

 

[davenn]

Hi Kiwan
welcome to electronics Point

I am confused as i dont understand VSS and VDD.....as in what is the difference and how can i appply it..

also when you look at the circuit most of the +- 9V VSS VDD are connected to ground
a bit confusing

with your two 9V batteries connected in series, the VDD goes to the positive terminal of one battery, the VSS goes to the negative terminal of the other battery.
The ground ( 0V) goes to the positive and negative termanials that are connected together

this is called a split supply

cheers
Dave

 

[kiwan]

thank u

thank you

that makes sense

i am now assuming my right leg connects to this ground but i am not getting results i am expecting

 

[davenn]

not sure what you mean by "right leg" ?

 

[(*steve*)]

not sure what you mean by "right leg" ?

It's the thing that your right knee is in the middle of

ECG machines have a number of connections around your chest, and a reference connection as far away from your heart as you can get, That's typically your right ankle.

Yeah, depending on the circuit, the ground connection probably goes there.

 

[davenn]

It's the thing that your right knee is in the middle of

well I was thinking that but wasnt sure LOL

Dave

 

[OLIVE2222]

with both sides of the optocoupler sharing the same power supply, how the isolation is provided? Is the optocoupler linear?

 

[kiwan]

to OLIVE2222

you have a good point there .....maybe if i placed a transfomer to provide the isolation.....???? what do you tink ??? or use two more optocoupler to provide isolation because a transfomer wud kinda be to big

is there a way i can make the optocoupler linear ????

this is the ones i am using

http://docs-europe.electrocomponents.com/webdocs/0f9a/0900766b80f9a553.pdf

 

[kiwan]

to davenn

I understand what you are saying but my circuit diagram doesn't make sense to me

im confused so vdd + 9 v will also be connected to the common ground at same time

wen doing pin 4 of the opto coupler???

 

[OLIVE2222]

A transformer,can be used but you need a circuit to drive it.
An isolation amplifier can be used too, see here:
http://www.ti.com/lsds/ti/amplifiers-linear/isolation-amplifier-products.page
The used optocoupler (or equivalent) can't be make linear. However linear optocouplers exist like the IL300.
http://www.vishay.com/docs/83622/il300.pdf
http://www.vishay.com/docs/83708/appn50.pdf
What do you mean by "use two more optocoupler to provide isolation" ?

 

[davenn]

to davenn

I understand what you are saying but my circuit diagram doesn't make sense to me

im confused so vdd + 9 v will also be connected to the common ground at same time

wen doing pin 4 of the opto coupler???

0V the connection between the 2 batteries is the Ground connection
There are actually only 2 connections to the GND shown and that's in the bandpass filter on the output
The output signal will also be between the output terminal and ground

they really did confuse the issue by showing the same GND symbol for all the power connections as well
that is poor circuit drawing !!
I can understand what they are doing with the symbols there, but for a newcomer its confusing

Dave

 

[kiwan]

hi

"with both sides of the optocoupler sharing the same power supply, how the isolation is provided? Is the optocoupler linear?"

what is wrong with them sharing same power supply .......

the purpose of the optocoupler is to provide isolation for the patient and the instrumental amplifier .......


I am a newbie to electronics so willing to learn by applying knowledge

wat i am trying to do is improve this circuit and add on to it........but i must understand it first and get it to work .........i want to add protection circuits and ADC

eventually make it a 12 lead ecg

 

[OLIVE2222]

The aim of the optocoupler is to isolate the user from the measurement equipment, here the scope.
If you use the same power supply on both isolation sides the isolation is bypassed and the user can be exposed to electrical shocks.

You project is hosted by a college of engineering, assuming we talk about a school assignment all we can do is point you to the right direction . Google a bit with ECG schematic, ECG circuit, ECG isolation and you will find handy information's to go further. By the way better to do it step by step.Starting with the front stage without isolation, then add the inputs protection, then the isolation then think about 12 leads version.
Olivier

 

[kiwan]

Thank you for the help

I am going to take a week and do some research on how i can improve the circuit bit by bit