CapSense Performance Tuning with User Modules
CY8C20xx7/S CapSense
®
Design Guide
Doc. No. 001-78329 Rev. *E
35
fs
max
= 3 MHz
4.1.3 Importance of Baseline Update Threshold Verification
Temperature and humidity both cause the average number of counts to drift over time. The baseline is a reference
count level for CapSense measurements that is an important part of compensating for environmental effects. High-
level decisions, such as Finger Present and Finger Absent states, are based on the reference level established by the
baseline. Because each sensor has unique parasitic capacitance associated with it, each capacitive sensor has its
own baseline.
Baseline tracks the change in counts at a rate set by the Baseline Update Threshold parameter. Make sure to match
the update rate to the intended application. If the update rate is too fast, the baseline will compensate for any
changes introduced by a finger, and the moving finger will not be detected. If the update rate is too slow, relatively
slow environmental changes may be mistaken for fingers. During development, you should verify the Baseline
Update Threshold settings.
4.2 Tuning the CSD/CSDPLUS User Module
is a flow chart showing the tuning process for CSD/CSDPLUS UM parameters. CSD/CSDPLUS UM
parameters can be separated into two broad categories: low-level (hardware) parameters and high-level API
parameters. The parameters in these categories affect the behavior of the capacitive sensing system in different
ways. However, there is a complementary relationship between the sensitivity of each sensor as determined by the
hardware parameter settings and many of the high-level parameter settings. You must consider this fact when you
change any hardware parameter to make sure that the corresponding high-level parameters are adjusted
accordingly. Tuning CSD/CSDPLUS User Module parameters should always begin with the hardware parameters.
