echelon


Building a simple ECG Amplifier

A friend and I joined forces to build a simple ECG (or EKG) Amplifier for our Signal Processing class at University of Applied Sciences Regensburg. We searched the web, magazines and books for suitable circuit diagrams and instructions on how to build one. We found that the instrumentation amplifier INA121 (datasheet) was a suitable IC and also the precision instrumentation amplifier AD624 (datasheet) mentioned in this Scientific American article seem to be viable option. However as it turned out those ICs are very hard to come by and rather expensive ranging from about $10 to over $50.

We also found a quite professional solution in Funkamateur, edition 12/93, pages 794-796. The article is in German and can be found here. We found another very simple circuit diagram for an amplifier in Elektor, edition 7-8/2000 that we ended up building. Here’s the diagram:

The components cost about 10 Euro. We built it on two breadboards one for the amplifier itself and one for the power supply. With two 9V batteries connected it supplies -9V and +9V. Here’s a picture of the amplifier board:

Green red and black cables are connected to the power supply, the thick black cables are connected to the subject and at the bottom there are two pins to connect the oscilloscope probe or an AD-converter.
We used real ECG pads from the hospital to collect the signal from the subject. At first we used regular unshielded copper cables to connect the electrodes which resulted in a lot of noise. We then replaced the copper cables with shielded thin microphone cables and connected the shield to ground. This hugely reduced the signal noise. Here’s an image showing an EKG taken with our amplifier:

The electrodes are connected to right hand, left hand and right foot. As you can see it’s pretty much what you would expect. You can see the P-wave, the QRS-complex and the T-wave. We’re quite happy with the results.

If you try to build something like this yourself please be advised that you should be careful when connecting this amplifier to anything that carries high voltage (line voltage). The amplification circuit and measuring devices are not separated from each other. So you should only use battery powered devices like a USB oscilloscopes connected to a laptop running on battery. This is important as you consciously connect the subject to your circuit in a very well conducting manner (because that’s what you want) and at very dangerous points. So you should take care that no high voltages can flow between the electrodes at any time.



52 Comments »

#1 wael wrote on January 3, 2009:

Hi

Thanks for sharing this great project

my quiz is :

can i use soundcard-based oscilloscope software “like zelscope for ex.” to preview thoe output of this circuit ?

wating your answer , and explanation

thnx

#2 Sebastian Schaetz wrote on January 3, 2009:

wael, I think it should be possible to use a soundcard-based oscilloscope. They usually provide a frequency range of 20Hz to 20kHz which should be enough to capture an ECG signal. Hope this helps :-)

#3 wael wrote on January 3, 2009:

thank you for ur reply

so , are you sure ? as i have less than 10 days to build an ECG project for my University .
is this picture in here taken from an Oscilloscope or Sound-card Oscilloscope ?

and if no , is there any chance that you try it , using this free software in here
http://zeitnitz.de/Christian/Scope/Scope_en.html

scince some people told me that the sound card cuts off the frequecies below 20Hz , so , can you tell me what the output frequency of this circuit ?

thank you again , really apreciate your reply

#4 Sebastian Schaetz wrote on January 4, 2009:

wael, to answer your question the picture is taken from an USB Oscilloscope (Velleman PCSU1000 – http://www.vellemanusa.com/us/enu/product/view/?id=522377).

I tried the scope software. Unfortunately I can’t test it with the circuit as I don’t have it here at the moment. However from what I can tell the scope is able to display an ECG. It can display the voltages (a few hundred millivolt) and an appropriate time range (10 seconds max). I believe you should be able to see an ECG with this scope.

Just think about what you expect: the normal heart rate is a about 60-80 beats per minute so you get somewhat between 1 and 1.33 beats per second so if the scope can display 10 seconds max you can display about 7 beats. Should be fine.

However I did not try it so no guarantees :-) Good luck!

#5 wael wrote on January 4, 2009:

well, thank u
seems that i have to build it and try it myselfe,but i’v some questions abt the circuit i can’t really figure out
1-what is this structure in the middle “cw p1 5k”? is it a normal resistor ?
2-what the “UB+” and “UB-” for the 4 BAS45A diodes stands for?
3-should i build the power supply like this ? or any 9v source ?
i red the datasheet of TLC274 IC , it can operate in range start from 3v , and i really want build the circuit in very small size , even i’ll use SMD components, so will the 3v battary do the job?

sorry , itz beginners questions i know , but really ur answers will be appreciated

#6 Sebastian Schaetz wrote on January 4, 2009:

1. a rotary potentiometer
2. UB+ and UB- is positive (+9V) and negative (-9V) voltage from the power supply
3. yes you should build this power supply and use two 9V batteries

I doubt it will work with a 3V power supply (the amplification should be proportional to the supply voltage).

#7 Claudiu wrote on January 15, 2009:

To add my thoughts about this project (I’m the mentioned friend with whom Sebastian built this): If you plan to build this yourself, and are, like us, quite a newbie in electronics, be prepared for some frustration :) At some times, the thing just wouldn’t work (the output was nothing like the expected one) and we couldn’t find any problems… I wouldn’t build this one a second time, I’d choose one that’s better explained (like the one in Funkamateur). All in all, it was a fun experience anyway..
Btw, Sebastian, why don’t you also upload the presentation?

#8 ieda wrote on January 20, 2009:

wanna ask something… in the schematic, i saw 4 ic’s, but why on the board, there is only 1 IC???

#9 Sebastian Schaetz wrote on January 20, 2009:

ieda,
thanks for your comment. I made the same mistake when I first saw the schematic. It is only one IC that has 4 amplifiers on it. As you can see in the schematic it says IC1a IC1b IC1c and IC1d. So it’s the same IC but different pins – IC1a for example are pins 1 through 3, IC1b are pins 5 through 7 and so on. Pins 4 and 11 are used for the power supply.

#10 Mohamed wrote on April 10, 2009:

please what is 49k6 ohm this mean what ?
is this mean 49k ohm or what?

#11 Sebastian Schaetz wrote on April 10, 2009:

Mohamed,
yes you almost got it. 49k6 is 49600 ohm.

#12 Mohamed wrote on April 11, 2009:

thanks for reply you help me alot in my graduation project in my faculty of engineering i search alot about ad620 and ina series and i didn’t find it to buy in Egypt so i’ll connect this circuit and hope to work correctly
but i didn’t know why they write resistance 24k9 by this way not only 24k?!!

#13 Mohamed wrote on April 13, 2009:

BAS45A diodes stands for? i see in ur pcb that are ziner diodes and what is their reverse voltage?
are their usage as protecting diodes?
I build this circuit but without the diodes i got heart wave but alot of noise and it is very sensitive to any move to my body
i need help waiting ur reply

#14 Sebastian Schaetz wrote on April 13, 2009:

Mohamed,
cool thing that you built the ECG amplifier.

BAS45A are those diodes: http://www.datasheetcatalog.org/datasheet/philips/BAS45A_2.pdf – we could not get them from our local electronics supplier so he gave us similar diodes. Unfortunately I can’t recall which diodes we used. They are used as protecting diodes yes. I think you can use any diodes that match the specifications of the BAS45A (see datasheet).
As for the noise we had the same problems. First of all you should probably use shielded wires to connect the electrodes to the body. We used a thin shielded microphone cable and connected the shield to ground on the circuit board.
Additionally the German article in Elektor explains how to configure the common mode rejection ratio. The article is here http://78.46.66.194/~cherry/ekg/elektor.pdf in german – I’ll try to translate the passage:
Balancing the CMRR is done using the trim-pot P1. Connect both the inputs of the amplifier to a 50Hz 100mV AC voltage based on ground. Measure the output of the amplifier and adjust it to a minimum using P1. I hope this helps.
I’m not sure how to work around the sensitivity to body movement though.

#15 Mohamed wrote on April 14, 2009:

my be my problem tha i use LM324 instead of TLC274 because i didn’t find it in egypt
I’m thinking about buying ad624 to build my circuit because I got fed up
and thanks alot for your interest

#16 Scott wrote on August 23, 2009:

Cool stuff! I did something similar with a single op-amp (<$1) using non-shielded cables and simple, free audio editing software to eliminate most of the electrical noise. http://www.swharden.com/blog/2009-08-14-diy-ecg-machine-on-the-cheap/

#17 Sebastian Schaetz wrote on August 23, 2009:

Scott, thanks for your comment. Your project is excellent – I actually like it better than ours :-)
Your project and our project are an excellent example for how you can solve the same problem differently – either with hardware or software. Your circuit is simple and cheap and you use software for the fun part. We have more hardware but don’t need any filtering software to see the ECG. In the end I’m guessing it is – as always – cheaper to write software because you only have to write it once, no matter how many units you produce.
Thanks for sharing this and keep up the excellent work.

#18 Oscar wrote on September 15, 2009:

Hi:
Thanks for this project. I am thinking about building the circuit, but I have some questions:
Is the “inverted T” symbol in the circuit the ground (just like the symbol of the 10 pin in the TLC274)?. Must I connect all these together and to the ground?
I do not understand the symbol just below the K1 at the end of the circuit. Is it for the scope?
I am planning to use a soundcard oscilloscope. Do you know if wael was successful with his soundcard scope?
Waiting your reply,
Thanks a lot

#19 Sebastian Schaetz wrote on September 15, 2009:

Oscar, thanks for your comment.
The inverted T-Symbol is indeed the common ground. All of those have to be connected together. The symbol at the end of the circuit is the connection to the oscilloscope.
If you’re a beginner in electronics and want to use the soundcard I strongly suggest to not build this one but the much simpler and better DIY ECG by Scott Harden. It only needs a hand full of components – all the filtering and other signal processing is done in software. Check it out here: http://www.swharden.com/blog/2009-08-14-diy-ecg-machine-on-the-cheap/

#20 Oscar wrote on September 16, 2009:

Sebastian, Thanks a lot for your reply.
I have seen the Scott Harden ECG and it is a great project too, but we need a hardware based project rather than a software based project for our school, so I think that finally I will try to build the circuit. If the soundcard do not work, we will try to get a cheap usb oscilloscope.

#21 Sebastian Schaetz wrote on September 16, 2009:

Alright Oscar.
You could merge the two projects – build our circuit but use Scott’s techniques to postprocess the data. I think that should work. Good luck!

#22 tolman shrestha wrote on October 8, 2009:

thanks a lot for this project.
what is the name of the ICa, ICb……
please reply as soon as possible

#23 Sebastian Schaetz wrote on October 8, 2009:

tolman shrestha, as stated before ICa, ICb etc are the various amps of TLC274.

#24 tolman wrote on October 11, 2009:

please send me the name of the ICs used in the circuit. I have to submit my project within this 10 days.
so please help me by providing the detail of the circuit.
hoping for your reply very soon………..

#25 tolman wrote on October 11, 2009:

thanks a lot for your reply.
i need your additional support.
Can you send me any circuit with detail explanation for the wireless transmission of this ECG signal.

#26 tolman wrote on October 11, 2009:

sorry for another question………
I am the beginner of the project, so i have not enough knowledge of the circuit element.
In the circuit what is that P1 ( cw 5k) near the last terminal of the opamp?

#27 gaurav wrote on October 13, 2009:

yaa same questions as posted by tolman.

Please response these questions as soon as possible.

I have to submit my project within 15 days.

hoping for your enormous help for us…….

#28 asif wrote on October 13, 2009:

hi sebestian,
ich habe eine frage und zwar
nach welchem Prinzip hast du EKG gemessen?
Was für eine Role spielt hier rechtes Bein?
wie kann man d. Ausgangsignal mit Ozsilloskop messen (bzw. wie soll ich die verbindung zwichen Ozsilloskop und d.Ausgangsignal darstellen)?

auf eine schnellere Antwort werde ich sehr dankbar sein.
mfg
asif

#29 Sebastian Schaetz wrote on October 14, 2009:

tolman:
P1 is a potentiometer (http://en.wikipedia.org/wiki/Potentiometer) It is used to configure the common mode rejection ratio (http://en.wikipedia.org/wiki/Common-mode_rejection_ratio)

asif:
IC1c amplifies the common mode signal 31 times and puts it on the right leg. This has two effects. 1. the body is brought to a defined common mode level to keep the signals from the hands inside the input range of the amplifier. 2. the common signal is degenerated to achieve a even better common mode rejection. (this is translated from the original Elector Article)

Hope this helps,
Sebastian

#30 asif wrote on October 20, 2009:

Danke Sebestian….es hat geklappt.

#31 kumar wrote on November 27, 2009:

can we use this project to diagnosis purpose?
how to calculate the heart rate using the wave we obtained?
reply very soon

#32 Sebastian Schaetz wrote on November 29, 2009:

can we use this project to diagnosis purpose?

Absolutely not.
The heartrate should be 1/(period of ecg signal).

#33 nuhri wrote on July 7, 2010:

hi, i just wanna ask if this circuit can detect waveforms whose frequency range is from 0.5 Hz to 100 Hz. also, does this circuit include an instrumentation amplifier? if yes, what type of Instrumentation amplifier does this circuit use? thanks much. :)

#34 Sebastian Schaetz wrote on July 8, 2010:

The circuit uses the TLC274, an operational amplifier.
I’m not sure if the circuit could properly amplify from .5 to 100Hz, but I believe so.

#35 Rahimi wrote on September 24, 2010:

Hi,

i wanna ask, how to connect the circuit to AD converter?what is K1?is it oscilloscope probe?

#36 Sebastian Schaetz wrote on September 30, 2010:

Yes K1 is an oscilloscope probe.

#37 abdul wrote on October 7, 2010:

please tell me equivalent diode of BAS45A?

#38 Sebastian Schaetz wrote on October 8, 2010:

Abdul, you can check the properties of BAS45A and find a diode with similar properties at for example farnell.com.

#39 Zohaib wrote on October 12, 2010:

man if does’nt use the BAS45A diode
what will be its effect on ckt, does it malfunction
and what will happen if we use IN4148

#40 Luis Carvalho wrote on November 16, 2010:

Dear Sir,

I have an atrial fibrillation and I would like to build your ECG amplifier to see my ECG.

But since I have not a laptop, I want to try first the amplifier with a sinusoidal wave of 1.6 v, created by an audio generator. This wave is reduced to 0.004 v, with a voltage divider.

But I have a problem: how can I simulate the electrode applied to the leg?

Best regards,
Luis Carvalho

#41 zelin wrote on December 26, 2010:

hello sir:

i am just wondering if we can get some real inside working of this project wht actually is going on also can u tell if lm324 can be used instead of tlc274

regards

#42 Uttam wrote on July 15, 2011:

Sir,
Here TLC274 is used, but unfortunately I am not getting this IC easily, I find TLC271 or TLC272 having single opamp and band width, Db and other parameter almost similar to TLC274, and TLC272 and TLC271 are available easily,
Can i build this circuit by 4 nos. TLC 272 or TLC271 ics keeping other component same, will it effect the performance /output of the circuit. Please reply,
regards,
Uttam Dutta
u.dutta@tatasteel.com

#43 Ionut wrote on March 11, 2012:

Can you post a picture with the back of the pcb to see how the components are connected?

#44 Ionut wrote on March 19, 2012:

I tried the scheme with 324 and Zeitnitz Scope and laptop sound card -it doesn’t work.:(

#45 Ionut wrote on March 21, 2012:

I tried the scheme with tlc274 and Zeitnitz Scope and again…it gives only squared waves.So it doesn’t work.Something is fishy here…

#46 wiseacre wrote on February 9, 2013:

K1 is a connector. Schematic symbol is not exactly defined and can vary from author to author. The symbol is simplified drawing of what you can see inside of jack connector socket.
http://en.wikipedia.org/wiki/Phone_connector_%28audio%29#Configurations_and_schematic_symbols
http://i.stack.imgur.com/xASEt.jpg
http://www.cui.com/Products/Image/GetProductImage/3219?typeCode=M
If you do not know this, then you probably not know many other electronic principles and your project will be most likely fruitless.

#47 Sebastian Schaetz wrote on February 14, 2013:

Wiseacre, I disagree. It is really quite irrelevant what connector you use here. Your comment about fruitless projects due to ignorance of electronic principles is not applicable here as well as offensive.

Cheers,
Sebastian

#48 Nicholas Ng wrote on February 15, 2013:

Hi sebastian,

I am doing a project on analysing ECG patterns of a subject, something very similar to this project that you have done. So I am not very experienced with these electronic equipment but I managed to build up the circuit. I am using an oscilloscope from leCroy 44Xs-A but whenever I connect the electrodes to myself, all I see on the oscilloscope is noise. I am using single core shielded wires too.

May I know what is the voltage (when the electrodes are not connected to my body) between the point of the oscilloscope probe and the reference point? currently mine is reading a low 40mV

#49 Nicholas Ng wrote on February 15, 2013:

Hi again,

I forgot to mention that even after I connected the circuit together. The output at the oscilloscope is a constant square wave. Any idea what’s wrong?

#50 Sebastian Schaetz wrote on April 1, 2013:

Hi,

a caveats I encountered when building this ECG amp was the time scale of the oscilloscope. The human heart beats abouts 1 time per second so make sure you select the proper time scale when looking at the signal. In addition, the amplifier did not work extremely reliably – so I suggest you experiment a little.

Good luck,
Sebastian

#51 Bhga wrote on October 23, 2013:

Hi
I am donig a projet on Ecg i want to use Fingertips insted of elctrodes so
can you help me how can i get the same accuracy from finger …..?

#52 Sebastian Schaetz wrote on October 24, 2013:

Hi Bhga,

yes, fingertips should be find. Check out this website http://www.swharden.com/blog/2009-08-14-diy-ecg-machine-on-the-cheap/ for more information on building an ECG and also check out the section “The Electrodes” for information on how to build the electrodes.

Please take all the necessary saftey percautions when hooking yourself or another person to an electrical device.

Sebastian

Leave a comment