Hello Jonathan,
I would like to share some recommendations in order to improve the sensitivity of the MPR121:
1. You can modify the sensitivity of the MPR121 by adjusting the value on some registers, please check the application note on the following link to find what changes need to be done:
AN3889 - MPR121 Capacitance Sensing Settings
2. Please note that using a bigger electrode size, the sensitivity will be improved.
3. Decrease the Touch Threshold Value (on registers 0x41 – 0x57 depending on which electrodes are you using), I don’t know your current value, but you can try to set different values and use the one that works fine with your application. But typically we recommend a threshold values in the range between 0x04 and 0x10.
4. Modify two configurable components: the electrode charge current and the electrode charge time.
The electrode charge current can be configured to equal a range of values between 1 μA and 63 μA. This value is set in the Charge Discharge Current (CDC) in the Analog Front End AFE Configuration register (0x5C). The electrode charge time can be configured to equal a range of values between 500 ns and 32 μS. This value is set in the Charge Discharge Time (CDT) in the Filter Configuration Register (0x5D).
For more details about this, please take a look of page 14 of the MPR121 datasheet.
Finally, you may refer to the following application note in order to get more detailed information about Designing Touch Sensing Electrodes:
AN3863 - Designing Touch Sensing Electrodes
I hope these recommendations will be useful for you.
If I misunderstood your question, feel free to let me know. I will be glad to help.
Have a great day.
David Diaz.
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