Sensing Technologies

[MaNi_3017621]

Hello,

I am trying to read DEBUG_DIFFERENCE_COUNT0 register. We have designed our PCB with CY8CMBR3116 and 12 buttons and it is working fine for button touch detection. Now I want to evaluate its performance. So, I am reading DEBUG_CP and DEBUG_DIFFERENCE_COUNT0 registers. I have written the button id to SENSOR_ID register. DEBUG_CP values seems to be ok but DEBUG_DIFFERENCE_COUNT0 value is always 255 when there is touch and 0 when there is no touch. But if we place a finger at a distance of about less than 1cm from button, it gives values between 80 to 250. So, I referred Capsense design guide for capsense performance tuning. According to this document, if DEBUG_DIFFERENCE_COUNT0 is greater than 50 counts, SNR should be in the ratio 5:1. So, to understand these settings, I started working on CY3280-MBR3 evaluation kit and trying to evaluate this on the button provided on evaluation board.

So I created a project on EZ-Click V2.0 and its settings are as follows.

In Capsense design guide document, for noise count measurements, it says

So, I tried same on evaluation kit. and getting following waveform.

For signal measurement, in Capsense design guide, following is suggested.

But when I tried on evaluation kit, I am getting,

unlike in Capsense design guide, in my case, baseline level also changes. So, I am not getting how to measure the signal. Or Is there any other setting that is needed?

After tuning the capsense performance on evaluation kit, I can try to tune my customised PCB also.

So, Please let me know what needs to be done in this case.

Thanks in advance.

Mamata

[NoriakiT_91]

It seems that the touch is not recognized because the diff count is lower than the finger threshold.

In your project, the check box "Automatic threshold" un-checked.

Please confirm if the CapSense works when the "Automatic threshold" checked.

The reason why the baseline is changed to the raw count level is the "Auto-reset period" is enabled in the "Global Configuration" tab.

Regards,

Noriaki

[MaNi_3017621]

Hello Noriaki,

Thanks for your response.

As suggested by you, I have checked the box 'Automatic Threshold'.

I get following waveform,

Here, it shows the difference of 750 counts in the raw count when sensor is touched.

Thanks,

Mamata

[LinglingG_46 · Accepted solution]

1: Unlike in Capsense design guide, in my case, baseline level also changes. So, I am not getting how to measure the signal. Or Is there any other setting that is needed?

    Because you enable the feature "auto-reset". You can choose  "disable" to disable the auto-reset function.

2: Uncheck the “Automatic Threshold”, if the diff count is 750
which more than 255, you can change the sensitivity from 100 to 400 like below:

3: We should change the finger threshold depending on the signal.

3:More you can refer to the MBR capsense design guide: https://www.cypress.com/documentation/application-notes/an90071-cy8cmbr3xxx-capsense-design-guide

Section:  CapSense Performance Tuning

4: Hope it can be helpful for you!