Datasheet

22 Document No. 001-66271 Rev. *B CY8C21x34/B CapSense
®
Design Guide
Figure 3-6. Sensor State Versus Difference Count with Hysteresis Set to Zero
Equation 4
3.6.6 Debounce
The Debounce parameter prevents spikes in raw counts from changing the sensor state from OFF to ON. For the
sensor state to transition from OFF to ON, the Difference Count value must remain greater than the Finger Threshold
value plus the hysteresis level for the number of samples specified.
Possible values are 1 to 255. A setting of 1 provides no debouncing.
3.6.7 Negative Noise Threshold
The Negative Noise Threshold parameter acts as a negative difference count threshold. If the raw count is less than
the baseline minus the negative noise threshold for the number of samples specified by the Low Baseline Reset
parameter, the baseline is set to the new raw count value.
Possible values are 0 to 255.
3.6.8 Low Baseline Reset
The Low Baseline Reset parameter works in conjunction with the Negative Noise Threshold parameter. It counts the
number of abnormally low samples required to reset the baseline. It is used to correct the finger-on-at-startup
condition.
Possible values are 0 to 255.
3.6.9 High Level Parameter Recommendations
The following recommendations are a starting place for selecting the optimal parameter settings.
 Finger Threshold: Set to 75 percent of Difference Counts with sensor ON
 Noise Threshold: Set to 40 percent of Difference Counts with sensor OFF
 Baseline Update Threshold: Set to two times Noise Threshold
 Sensors Autoreset: Based on design requirements
 Hysteresis: Set to 15 percent of Difference Counts with sensor ON
 Debounce: Based on design requirements