i'm just starting using the MPR121, and so far i am highly fascinated.
However i am experiencing a startup time for the auto-calibration, that i would love to see a little lower. I am using 8 channels (0-7), and from power-up it takes the MPR121 around 5-8 seconds to settle. In the debugger of my processor i see the baseline values (0x1E through 0x25) settling towards the decimal values from ~24 to ~39, and when they are settled, touches are recognized nicely.
Is this normal behaviour? Is there any way to speed up the auto-calibration?
If i wouldn't want to use auto-calibration, what steps would i need to do to manually calibrate the MPR121?
Would it be good practice to store the settled baseline values in flash memory, and use them to initialize the MPR121 at startup? I have also noticed, that when i use defuined baseline values at startup, the auto-calibration will only correct them upwards. I.e., when i preset a channel with baseline=30, where ~24 would be the value at which the calibration would settle, then this value stays at 30 and false touches are recognized.
I'd be glad to hear some of our insights to that startup topic.
Thanks a lot,