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Posts: 9
Registered: ‎08-28-2017

CPT112S misses events on I2C

Hello,

 

 

Trying to operate the CPT112 with STM32F446,

I see that some of the device misses events mostly on release but some of them are on touch events also, in the simplicity studioevents looks fine,

when i probe the INT pin i see that i does not change when it misses the events so its not related to problem with the STM32/code issues.

 

 

Thanks.

Itamar

 

Posts: 2,384
Registered: ‎10-14-2014

Re: CPT112S misses events on I2C

Do you mind uploading a picture to show the capacitive profiler data when the touch and untouch happen?

What's the criteria you draw the conclusion that the event missed, how much do you the capsense data change when the event happen?

 

WeiguoLu
Posts: 9
Registered: ‎08-28-2017

Re: CPT112S misses events on I2C

Events looks good on the profiler, 

i probe with scope the I2C SCL/SDA, and INT, sometimes it misses the events.

 

Posts: 2,384
Registered: ‎10-14-2014

Re: CPT112S misses events on I2C

Looks like the data difference is small between touch and untouch.

Have you customized the CPT112S?

Are you working on a TB board from Silabs or a custom board made by yourself?

If you are working on a custom board made by yourself, maybe you could try to customize the CP112S to see if you could detect the touch and untouch reliably. There are some application note address how to customize the CPT112S.

WeiguoLu
Posts: 9
Registered: ‎08-28-2017

Re: CPT112S misses events on I2C

I'm using the CPT112S evaluation board, soldered some custom pads to the CS pins, after several tries device doesn't seems reliable enough for commercial use.

 

I have configured the configuration at simplicity studio:

Capactive.png

 

Attached STM32F446 internal pull-up resistor on the INT pin, device seems work better with the resistor, but still misses events. any ideas?

 

 

Appreciate your help,

Itamar

 

Posts: 2,384
Registered: ‎10-14-2014

Re: CPT112S misses events on I2C

Since you made some change on the CPT112S board, I would suggest you fine tune the configuration data to match these change with the capacitive sense profile tool. 

By the way, do you see similar issue if you did not made change on the CPT112S board (missing event)?

I am wondering why the pullup on INT pin could have effect on this issue, it was strange to me.

 

My views are my own and do not necessarily represent the views of Silicon Labs

 

WeiguoLu