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ADS1298ECG-FE. Data Read-back error

Mohd Aslam85
Prodigy 160 points

Hello,

I'm currently working on my Arduino Uno + ADS1298ECG-FE project. I have verified hardware connections because I'm able to read back Device ID, read/write to registers. I have an ECG simulator (ST-16 ECG Simulator/Calibrator). 

Prior to starting work, I've tested my simulator with the ADS1298ECG-FE Product Demonstration Kit (i.e, with MMB0 board and software provided). I manage to read an ECG signal using the software. I use the same register values that the software uses to read ecg without any problems. The following image is a screenshot of the register settings used by the evaluation software. 

When I am using the same register settings for my Arduino code, I am facing a problem. (For simplicity, I am only reading back Channel 1 now). The data that I am constantly getting for channel 1 is 0x7FFFF. According to the following image below, 0x7FFFF means that I have exceeded the range. My assumption is that my ADS1298ECG-FE is currently reading a signal that is above its allowed range (i.e. it is saturated?). 

Is there something that I am doing wrong? I tried changing the gain from 6 to 1 via the appropriate registers but to no avail, I still get 0x7FFFF. 

Earlier, I tried generating internal square wave test signals and have been more lucky as opposed to normal electrode measurement. This is the result of my internal test signals. I'm not sure if why it isn't a perfect square wave but I can guess that it may be due to the manner in which i save/post-process the data sent back to my computer.

I don't know if this is correct, or it happens to look a little like a periodic square wave by chance. However, it seems better than the 0x7FFFF from normal electrode measurement. 

Do you have any suggestions as to why I'm constantly reading a maxed out 0x7FFFF signal? Given that I can read device ID, and read/write to registers etc, we can rule out hardware connections causing a problem. In addition, having used the same ecg simulator with the provided ADS1298ECG-FE evaluation software, I am positive that the simulator isn't spoilt or sending a voltage that is too large. 

It would be great if you could advise the potential problems that is causing this. 

Any information would be extremely valuable and helpful. 

Thank you again.

Best rgds,
Aslam

  • 0
    Prodigy 140 points
    What about your schematic?
    How did you connect, DRDY, START to your Arduino?
    Do you start conversion by hw or sw?

    Regards,
    Evert
  • 0 in reply to Evert Dekker
    Prodigy 160 points

    Hi,

    I've managed to find out the cause of the problem. It is due to not setting the Wilson's Central Terminal properly. Fyi, DRDY and START pins are connected as inputs and outputs of the Arduino respectively.

    This is the data for Channel 1. I'm currently sending data from my microcontroller to the PC via the serial terminal, which takes time. As a result, I suspect that I am losing samples, resulting in an inaccurate waveform.