I would need some support on new questions we have about the ADS1191. Just to remind you, our use case is the following : the user will put the device on and must be able to perform an ECG measurement as soon as the device is in place. The measurement will last 20 seconds or so. The "ERA" electrode is connected to one arm, and the "ELA" and "RLD" electrodes are connected to the other arm. We are using dry electrodes.
The "ELA" electrode is connected to IN1P, and the "ERA" electrode is connected to IN1N, through 51k resistors (in place of R71 and R63). The following components are "DNI" compared to the initial demoboard schematic: R16, R85, R73, C92, C60, C56, C91, C89, C90, R62, R64, R66, R72, R69, R70, C47, C45. And the following components are 0 Ohm resistors: R116, R118, C48, C46, C50, C49.
We are using the following registers :
00h : 50
01h : 02
02h : e0 (2.42V reference)
03h : f0
04h : 00 (Gain1 = 6)
05h : 00
06h : 3f
07h : 0f
08h : 03
09h : 02
0Ah : 02 (RDLREF is fed internally)
0Bh : 0c
The problem is that the contact with these dry electrodes seems to take some time to be effective, and then, the analog signal will take some time to be between -0.4V and +0.4V (reference/gain). The order of magnitude of this time is 30 seconds depending on the humidity of the arms, but we would need it to be inferior to 5 seconds or so.
Do you have any advice to solve this issue (other than lowering the gain, which would lead to a loss of precision)? Maybe by modifying the external components between the electrodes and the ADS1191? Or by changing some registers?
You'll find attached an example of the SPI saturation during the first 13 seconds of the measurement, which we cannot afford.
Best regards,
