ECG device

[zelin]

Hi guys

i need a bit help if anyone can i am making an ecg amplifier using this circuit mentioned in elektor

http://www.soa-world.de/echelon/wp-content/uploads/2008/12/elektor.jpg


according to journal the right/left arm signals are amplified with 201 gain and feedback signal is amplified 31 times and then attached to right leg to provied better CMRR and should neutralize the common mode signal between them

ic4 merely is used to set CMRR by changing potentiometer

the problem i am facing is my signal when comes out of ic 1 and ic 2 is saturating its a 50hz noise signal if i am right... the feedback purpose was to remove this saturation but i cant get it right i have made exact circuit and just this modification that instead OF 24K9 resistors i got 24k3 but i added 600 resisters to them


if anyone can help me over that ASAP pls

 

[OldTechie]

Questions to ask yourself:
Are you using the battery power supply as indicated on the schematic?
Is the instrument connected in any way to 50Hz mains?
Are the signal leads shielded?
Is the circuit supposed to be mounted inside a metal shielded case?
How are you connecting your test equipment? Is it introducing the 50Hz signal into your circuit?
Does the Elector article indicate how to connect test equipment so it doesn't affect the operation?

Cheers,
Dave M

 

[zelin]

yes sir i am using exact configuration how ever my voltage levels are 17 volts .. its battery problems, thy are nvr idealy 9 v
THE only instrument attached to it is an oscilloscope but i tried a computer based ossiloscope too >.<. this guy who made it nvr sheild the whole circuit however i will today test with coaxial cables. and regarding to elktor article it just tells wht i told u above just one page article.


i got this guy he had the same problem but dono how he resolved it he nvr mentioned

https://www.electro-tech-online.com/threads/ecg-device.28243/

 

[audioguru]

Most students who cannot obtain modern intrumentation amplifier ICs make an ECG circuit with opamps that does not work.
Make the circuit that is shown in the datasheet for an instrumentation amplifier IC. It has built-in resistors that are very well matched so that the circuit works perfectly. the input cables are shielded (coaxial0 and the gain of the instrumentation almplifier iC is kept low enough that it doesn't clip the signal then the right leg driver IC cancels most of the common-mode hum so that another opamp can filter the signal and add a lot of gain.

 

[zelin]

this circuit is not bad it is mentioned in elktor and is not a normal opamp with CMRR of 80db if this guy at soa did it why cant i

 

[audioguru]

The resistors in the differential amplifier at the input of an ECG circuit must be extremely well matched. They are extremely well matched inside an instrumentation amplifier IC.

 

[SABorn]

why cant i

Well you can, but as AG tried to tell you if you want a "A grade circuit" than there is better ways, but if you are happy with a "B grade circuit" than by all means carry on.

Pete.

 

[koolguy]

Hi, good post....!!

 

[zelin]

i got it but the ics are not avaliable in third world country so i have to live with it . i am using shielded copper wires and have attached shield with ground too ... today i got some hints of ecg beats when i attached these wires i was much happy but now its the same again . ( i am using real ecg electrodes)


well AG i didnt got any 249 resistor but its 250-251 sometimes this cause problem? but i think it will only effect a bit gain...

 

[audioguru]

the ics are not avaliable in third world country.

I correctly guessed that you are in a 3rd-world country and cannot buy modern commonly available parts like we can.

 

[zelin]

yes but i need a bit help now LOL

 

[audioguru]

Why should I mail a modern IC to you?
Since you can't obtain modern electronic parts then do gardening instead of electronics.

 

[koolguy]

Hi, good post going on..!!

 

[zelin]

i nvr asked u to mail me one i am just saying since i am a student in engineering and making this stuff without any guidance if u can help me out with reducing this noise signal and point out mistakes if u can so i might get it to work Please i have wasted like 14 days on this circuit baked 2 TLC 274 lol i aint going back until i get it to work if that guy can i can too


if u cant help pls stop spamming RITESH KAKKAR sir i am new here on this site dont know much stuff around

 

[audioguru]

Today we make mostly new circuits. You want to make an old circuit.
Some engineers on this side of the world built a working ECG circuit a long time ago when they were in university before instrumentation amplifier ICs were invented.
Look in Google to find one of those circuits. But maybe the circuits were made before personal computers were invented.

Ask your teacher to help you match resistors so you can make your own instrumentation amplifiers.

 

[zelin]

like they are gonna help lol if thy would why would i be asking u thanks for ur help tho if anyne else got any ideas do share me