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?!
I have looked over the changes that you have made in the schematic and the code. Below are a couple things that I have noticed:
BrandonRamparo Hi Brandon and Glenn, I thought you might be able to help here.
To correct this here are some suggestions:
Let me know if this helps.
Hi Glenn, that solved the problem. K1 now reads 0.9989.
Thanks for your help!
You are welcome e669danesh. Glad to help.