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MPR121 Oscillating

Question asked by Nima Badizadegan on May 16, 2015
Latest reply on May 21, 2015 by Jose Alberto Reyes Morales

I just started using the MPR121 in a custom board, with pads laid out within the recommended tolerances (although the pads were on the large end, 13x13 mm).  I loaded the registers with the configuration specified in the quick-start guide.  The MPR121 is doing fine when no pads are touched, but when one of the pads is touched, the output in the status register oscillates between the "touched" state and the "released" state.  The time that the finger is on the pad increases the fraction of the cycle when it registers as touched. When the finger is removed, the pad continues to oscillate, and the duty cycle decreases, but never seems to reach 0 (ie the "touched" output continues to oscillate).

 

I have tried varying the filtering settings and the threshold values, but the oscillations continue to occur even when the touch and release thresholds are spread far apart (0x3F for touch and 0x05 for release were the most recent settings I have tried). 

 

Does anyone know what is happening here?

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