AGND Pinout
I was looking at the schematic diagram for the Cyton and I'm a bit confused, what is the AGND pin on the cyton connected to on the ADS1299?
Is it everything that is marked AGND? (Bias Reference, AVSS and DGND are all connected to AGND)
Why is it better to connect to the bottom AGND than the top?
https://github.com/OpenBCI/V3_Hardware_Design_Files/blob/master/OpenBCI Cyton Designs/OBCI_V3_32bit-Schematic.jpg
Comments
AGND in general should NOT be connected to the subject. This AGND is useful for Active electrode applications.
The current EMG document has an error for Cyton, and shows AGND, when it should use Bias. I thought this was queued to be corrected.
https://docs.openbci.com/docs/01GettingStarted/02-Biosensing-Setups/EMGSetup
As shown, Ganglion section of this document shows using the D_G pin for ground. Ganglion D_G is the same as Cyton Bias/Ground pin. The Bias pin is a proper high impedance connection to the ADS1299. Whereas AGND is a direct low impedance connection to the analog power supply. Generally you want connections to the subject to be high INPUT impedance, not low INPUT impedance. Of course regarding skin impedance, you want the opposite, LOW skin impedance.
William
Thank you!
We have updated the EMG setup doc for Cyton to mention connecting to the BIAS. TI data sheet recommends this in all diagrams and language. ADND/DGND pins are meant for chip/component/battery connections.
https://docs.openbci.com/GettingStarted/Biosensing-Setups/EMGSetup/