3 Replies Latest reply on Sep 26, 2018 1:10 AM by ring

CAP sensing raw data drifting problem (CY8CMR3102)

user_36905748 Sep 14, 2018 9:59 PM

Hi,

I started a new design with CY8CMR3102, used a STM32F103 MCU to configure and read the raw data from Sensor by I2C.

The PCB is a round shape(6cm diameter), a 1mm wide trace on edge of board as Proxmitiy sensor's antenna ( connects to CS0 pin though a 560ohm resistors).

CMOD is 2.2nF.

Here is the problem: the raw data I retrieved from sensor drifting a lot. In amibent temperature, the board will take 1 mintues to stay on the stable reading level. Then I put the board on temperature chamber running from -20(C) degree to +70(C)degree, monitoring the raw data, it will drift singanificant amount. I did try different configuration by setting different sensitivity value, different filters, enable/disable EMC function, but none of them can stop the raw data drifting.

My first guess is the whole pcb 's capacitance would impact the CMOD pin? Or some charging/discharing problem between the proximity sensor antenna and the ground plane?

Any suggestions/thoughts will be greatly appreciated!

1. Re: CAP sensing raw data drifting problem (CY8CMR3102)

ring Sep 15, 2018 10:47 AM (in response to user_36905748)

Why do you want to only get the rawcount? Or can you tell us why do you care the rawcount drift?
I think in some environment, the rawcount drift is normal. Capsense use the "rawcount - baseline" to decide whether the sensor has been trigger.
I think you should try to read the diff count.
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2. Re: CAP sensing raw data drifting problem (CY8CMR3102)

user_36905748 Sep 15, 2018 11:44 AM (in response to ring)

My first attempt is get the proximity status from sensor by reading the register, however no matter what configurations I chosed, the output always not as good as expected.

Then I read the rawcounts and designed my own algorithm to determine the baseline, calculate the ‘raw - baseline' and determine the proximity status . I did apply a certain level of differentiation, filters to distinguished different hand's movement, the output is much better.

However the rawcount is drifting, if I can fixed it, I will be able to generate the much better software for my application.

Any inputs will be appreciated.
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3. Re: CAP sensing raw data drifting problem (CY8CMR3102)

ring Sep 26, 2018 1:10 AM (in response to user_36905748)

rawcount is a testing result, not a calculate value, I think the user has no right to avoid it drifting.
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