AnsweredAssumed Answered

MPR121 with large electrodes for hand position detection gets stuck in detection.

Question asked by Enrique Romay on Oct 16, 2015
Latest reply on Oct 20, 2015 by Jose Alberto Reyes Morales

Hi, we are using the MPR121 for detecting the hand position on a bar (tube). hands may be positioned on the electrodes for a long time, 6 different areas must be distinguished,

everything seems to work correctly, but after some time electrodes randomly get stuck in detection state, resetting the sensors brings everything back to initial state.

 

vdd is 3v3

the tube has a diameter of about 3cm, and a perimeter of abour 9cm , we have 6 interdigitated copper electrodes with a shape like shown in the picture.

 

electrode_freescale.jpg

capacitive electrode is interdigitated with a grounded electrode to minimize proximity sensing and only detect touch. 3mm traces with a separation of 3mm.

The electrodes are covered with 1mm thick leather. total sensing area is about 125cm2, actual area of the electrode is about 33cm2.

 

configuration is based on AN3994. we disabled baseline filtering:

[0x5E] --> 0x00

[0x34] --> 0x00

[0x35] --> 0x00

[0x2B] --> 0x01

[0x2C] --> 0x01

[0x2D] --> 0x00

[0x2E] --> 0x00

[0x2F] --> 0x01

[0x30] --> 0x01

[0x31] --> 0xFF

[0x32] --> 0x02

[0x5D] --> 0x00

[0x7B] --> 0x0B

[0x7B] --> 0x0B

[0x7D] --> 0xCA

[0x7E] --> 0x83

[0x7F] --> 0xB5

[0x5E] --> 0x8C

[0x5E] --> 0x4C

 

do you have any idea about why can it be that the electrodes get stuck in detection state?

 

thank you in advance for your help.

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