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EVAL-CN0395-ARDZ configuration for Alphasense VOC-M31 gas sensor


After successfully testing EVAL-CN0395-ARDZ with its default sensor (Figaro TGS8100), I am now trying to make the necessary changes to make it compatible with an Alphasense VOC-M31.

To do so, I:

1. removed the TGS8100 sensor

2. replaced the 41.2 Ohm resistors on R17 and R19 with 2.2 Ohm resistors to extend maximum current to ~186 mA

3. connected VOC-M31 sensor 

There are a number of other changes that needs to be made in the firmware:

1. ADN8810.h: line 14, change ADN8810_RSN  from 41.2 to 2.2

2. CN0395.h: line 4, change ALPHA to 3255 (to match our sensor's heater TCR value)

3. CN0395.c: a number of changes to the temporal responses (delays, etc.) to account for the fact that this ceramic sensor is slower in responding to changes in heater settings.

By these changes I manage to get a signal from this sensor, but only if I use the default Gain Correction Factor K1 = 1.000. 

Every time I run the "calibration w" routine I get the K1 = 3.250 which is clearly wrong (it messes up all the current/voltage figures). So I suspect there are other changes needed to be applied to the firmware which affects this calibration?!

Please advise.