I am building an EEG module but I am stuck at impedance testing stage.
As of now I switch ON the internal current source on INxP pins and measure the impedance between this pin and BIAS_OUT (as current sinks there), SRB1 is connected to ground. Also the protection resistors on the channel pins are there. I take 10 second data for a channel and then apply the calculations on the voltage I get to obtain Impedance.
But the above story is for a single channel. In my ADS1299 module I have 8 channel. If I spend 10sec each per channel (disabling the other channel when one is working) so I will take 80sec just to measure impedance, which will give a poor user experience and user has to wait 80sec just to see if electrode is connected or not. Even if I reduce the time to 5sec per channel, it will be still take 40sec. Going below 5sec per channel is giving me an intuition that it is not sufficient to measure impedance as some settling time of stray capacitance has to be included.
If I switch ON all the channel's current source at once, there is a possibility of current going here and there all over the head and I won't get impedance between the points I am aiming for.
What could be the best way to measure impedance of all channels in minimum possible time?
I have referred article, EEG Hacker, for impedance measurement procedure.
