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ADS1299EEGFE-PDK: ADS1299EVM Human disturbance consultation

zhzhm1214
Prodigy 60 points

Part Number: ADS1299EEGFE-PDK
Other Parts Discussed in Thread: ADS1299

Hello.

I got a 2Hz, 20μV sine signal connected to the 1299EVM's REF and CH1 + (sample rate at 250Hz). However, when the human body passes by the acquisition device, there is a great disturbance in the collected signals. The waveforms in the figure below are the result after baseline removing and a 50Hz notch filter. Figure 1 is the normal acquisition of the sine wave, Figure 2 shows the waveform of channel 1 when someone walked by. Each irregular peak was caused by walking by. Figure 3 shows the waveform of another Input-shorted channel, which can be seen to be very disturbing.

I've done a lot of experiments with the devices and found that singal gets abnormal when the human body walks past the device, or someone is shaking a leg, or someone is jumping nearby,or even just someone is swing nearby. Moreover, there is still such a problem when using an aluminum box to swing around the acquisition circuit.

Based on the above questions, I’m confused with the EVM. Would you like to show me some solutions for such kind of problems?

Thank you.

  • 0
    TI__Guru**** 182881 points
    Hi zhzhm,

    Can we start by sharing more detail about the sensors you have connected to the ADS1299? Perhaps you have a picture of the setup that you can share?
  • 0 in reply to Tom Hendrick
    Prodigy 60 points

    Hi，TOM

    Thank you for your reply.

    Here is the setup example. ( In practical applications there is an aluminum shield outside )The input signal is a 20μV voltage divider signal of 100mv from a signal generator..

    I've also connected the real EEG signal directly to Ch1-Ch6. The human disturbance happened either.

    Thanks again.

  • 0 in reply to zhzhm1214
    TI__Guru**** 182881 points
    Hi zhzhm,

    Sorry for the delay in getting back to you. Have you tried using shielded cables, from the generator to the first board and then on the umbilical to the ADS1299 eval board?
  • 0 in reply to Tom Hendrick
    Prodigy 60 points

    Thanks，Tom

    Actually, the cable used in the figure is shielded cable. I've used a Iron box  as shielded box, but it didn't work. By the way, what's the recommended integrated circuit U2 used as a BIAS_SHD option? 

    Thank you~

  • 0 in reply to zhzhm1214
    TI__Guru**** 182881 points

    Hi zhzhm,

    In the picture you provided, I only see a black and a red lead emerging from the cable.  If there is a shield in that cable, it should be exposed and terminated to GND on both ends.  A shield without termination can act as an antenna and actually make things worse.  The op-amp that you choose for the circuit above depends on the capacitance of your cabling, you may also need a series R to act as a LFP.  I've not done any extensive testing with that circuit, so I don't have a specific amplifier to suggest at the moment.

  • 0 in reply to Tom Hendrick
    Prodigy 60 points
    Hi Tom,
    Thanks again for your timely and effective answers. I've learned a lot.
    Best wishes!