ads1299 using ac lead off. how to check the lead off status?

gazamgazam south korea
edited July 2015 in Other Platforms

Hi. I am working on 24ch eeg device with ads1299 chip.

And I need to check the impedance of leads.

my ads1299 setting is..

24 channels of lead connected to [-] input and all [+] input is connected to one reference

so I set the ads1299 LOFF register to 0x03(ac Fdr/4). In my case, it is 125Hz

and LOFF_SENSP to 0(zero) and LOFF_SENSN to 0xFF

I got datas in my pc and analyzed it with FFT

I expected that there shold be a power(?) in range of 125Hz only when lead is connected to reference

but I also got a amplitudes in  other channels which are not connected. other channels have 125Hz signal.

I thought that chennels affected by all [+] input tied one reference.

Is it working right? so I thought that I dont need FFT to check the lead off status. is it right?

I just calculate the impedance with only Vrms and current.

have two questions.

one. Do I need to FFT to know lead off status?

two. when measure the real eeg data, do I turn off the ac lead off function?

thanks.

have a good day.



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