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ADS1299 + Single ECG channel

twistx77
Intellectual 480 points
Other Parts Discussed in Thread: ADS1299, INA129

Hi,

 I'm working in a design where I already have a ADS1299 working with the eight channels in single-ended configuration. 

Now I need to add a single ECG (not EEG) channel to the device which will be sampled by the same MCU that reads the data from the ADS1299. 

I now I could use one lead of the ADS1299 to do that by connecting it to the chest but I need the 8 channels for EEG. I also thought of obtaining the signal from the EEG channels digitally which is possible but not always as good as having a separate channel so I discarded that option too.

At first I thought of using just the Delta Sigma differential amplifier to get the signal from the Ref Lead of the ADS1299 and an extra lead to the chest but since the ADS1299 is using -+2.5V supply the BIAS could damage my MCU.

So now I'm thinking of making a simple ECG amplifier using an INA129 or an AD620A to get the differential value of the ref lead and the extra lead and then the output could be amplified using an opamp using 3.3V single supply and from that to the MCU.

Do you think is there any other better way of achieving my goal?

  • 0
    Prodigy 160 points

    Hi Alex,

    the ADS1299 has only 8 A/D converters.

    So, are you thinking to superimpose the ECG signal to the EEG and then sort of extract it in the software later?

    Bernhard

  • 0 in reply to Bernhard Wandernoth
    Intellectual 480 points

    Hello Bernhard,

    Thank you for your response.

    I'm thinking of adding one more lead to the system and using the signal form that extra lead and the REF electrode used in the ADS1299, obtain the ECG signal using a instrumentation amplifier. The output of the amplifier would be filtered and then fed to my MCU which would do the ADC conversion. 

    Greetings!

  • 0 in reply to twistx77
    Prodigy 160 points

    Hi Alex,

    ok, I see. The ECG signal is actually huge compared to the EEG- you will be dealing with 1...2mV! So, if I understand you right, your concern is to use the same ground / reference as used for the EEG. I don't see any problem with that, actually.

    By the way: If you are going to use an earclip as reference electrode, you could also use that for ECG (optical). Just a thought...

    I'm not an ECG expert but I know that the signal quality is better when using two ECG electrodes. The ground / reference is for potential equalization, the differential input of your amplifier would then go to the two ECG electrodes.

    Bernhard

  • 0 in reply to Bernhard Wandernoth
    Intellectual 480 points

    Hi Bernhard,

    Thank you for your support. 

    I can't use the optical, "oxymeter" type of signal. I need it to be the electrical one. I don't need it to be perfect as in a proper ECG device but I need the signal to be able to relate changes in the EEG signal with the ECG. It is for research.

    Anyway, I just wanted to know if that would have any kind of problem and If it would be good enough just using the reference lead from the ADS1299 and an additional lead for the ECG.

    I've made a simple block diagram in the attached image. I hope that helps.