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  1. #1
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    Need help with ECG circuit using AD620

    Hi,

    Right now, I am designing a hardware circuit to read the ECG signal where the output signal will eventually be read by n oscilloscope. I have already build the circuit, using AD620 as the IA and OP177 GPZ as my op-amp. I am referencing my circuit from this website :

    http://ecgarduinomatlab.blogspot.sg/

    Right now when I connect the output of the whole circuit to the oscilloscope, this is what I get.


    http://obrazki.elektroda.pl/7722357300_1478750307.jpg

    Also, I took a picture of the signal output where it is just after the AD620 output. If you look at this picture, there is certainly an ECG signal but with a little noise. May I know what is wrong ?



    http://obrazki.elektroda.pl/4371445500_1478750459.jpg

    I would appreciate the help that I can get from you guys.

    •   Alt10th November 2016, 05:05

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  2. #2
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    Re: Need help with ECG circuit using AD620

    Hi,

    If you look at this picture, there is certainly an ECG signal but with a little noise.
    You are talking about the second scope picture?
    If so: Then you see what you like to see.
    It surely is not an ECG signal.
    * A quick view at the timing setup: 2.5us/div..
    * and a view at the displayed frequency: 435kHz
    tells me: this has nothing to do with an ECG signal

    The heartbeat rate is in the range of 40 (relaxed sportsman)... 200 (high physical stress) beats per minute.
    --> use a timing setup of 50ms/div .... 200ms/div

    Klaus



    •   Alt10th November 2016, 08:04

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  3. #3
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    Re: Need help with ECG circuit using AD620

    Hi guys,

    I managed to get an ECG signal with the circuit.

    20161117_154057.jpg

    Attached is an Image of my output signal.
    Right now what I would like to do is to transmit the analog signal into digital signal through Arduino UNO where the data can then be analyzed and process further in MATLAB.

    How do I go about doing that ? I dont have any prior knowledge in programming.



    •   Alt20th November 2016, 14:14

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  4. #4
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    Re: Need help with ECG circuit using AD620

    It's basically explained in your post #1 link:
    Code:
    Programación Arduino
    
     int val;
     void setup(){
     Serial.begin(14400);
     }
     void loop(){
     val=analogRead(A0);
     Serial.println(val);
     delay(20);
     }
    I guess there are much more ECG Arduino projects on the internet.



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    Re: Need help with ECG circuit using AD620

    Alright guys, I finally build a portable ECG device where by the ECG signal will then be sent to Arduino UNO where the data will be transmitted via Bluetooth and the waveform will be displayed on Android Phone. I've already built a circuit and have a good waveform. I also managed to successfully transmit the data via Bluetooth and gotten a signal displayed on the phone.

    Here is the problem. I just found out (unfortunately) that Arduino UNO only reads from 0 - 5V. However, my signal range from -220mV to + 550mV. That being said, the signal that is being shown on the phone are clipped or only halved are shown and the negative waveform disappears. How do I shift the whole signal so that its value starts from above 0V ? I have tried non-inverting summing amplifier and it does not work, or maybe it was wrong placement to built. I have attached a schematics of my ECG circuit for references. I am supplying my circuit with 1x 9V battery where the power is split into +4.5V/-4.5V. I also have successfully built an analogue 50Hz notch filter. If anyone knows how to solve this, please share. Also, if I were to add summing amplifier, where should I add it ?

    <a title="ECG_Revised.png" href="http://obrazki.elektroda.pl/6346456200_1484072723.png"><img src="http://obrazki.elektroda.pl/6346456200_1484072723_thumb.jpg" alt="ECG_Revised.png" /></a>



    •   Alt10th January 2017, 19:27

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  6. #6
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    Re: Need help with ECG circuit using AD620

    Hi,

    *** I deleted my first, wrong assumption regarding R2 and R3.****

    The whole circuit works on 9V and GND is the center of 9V.
    The output signal is positive and negative referenced to your GND.
    So the circuit is correct so far.

    But where do the signals go?
    I assume there is the problem, maybe it can´t handle negative voltages.

    Klaus



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    Re: Need help with ECG circuit using AD620

    No,R2 and R3 is part of the gain. It was a parallel resistance to get 500 Ohm, and with R1 being a variable resistor, the Gain goes from 201 to 2001.



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