Datasheet

CY8C21x34/B CapSense
®
Design Guide Document No. 001-66271 Rev. *B 35
 Under Global Settings in the CapSense wizard, assign one sensor under the category "Button". Select the
modulation Capacitor and Feedback resistor pin as well. Set the threshold setting mode as manual, and
disable the Median and IIR filters. Ensure that in the board, the Rb value is 15 K and the Cmod is 10 nF.
 Under the Sensor Settings tab in CapSense wizard, set "Sensitivity Level" to Low and "Finger Threshold" to
96.
4. Generate/Build the project with the sample firmware code provided in the user module datasheet.
5. Monitor the sensor raw count and calculate the SNR. Figure 4-6 shows the monitored sensor RawCount.
According to CapSense best practices, the SNR for a robust design must be greater than 5. The monitored SNR
in this case is found to be 9, which is above 5. Read SNR improvement techniques in step 7 if the SNR is found
to be less than 5.
Figure 4-6. Monitored Sensor RawCount
6. You can skip this step if precise controlling of finger threshold is not required by the application, or if the
automatic threshold setting mode is selected. The automatic threshold mode uses an algorithm that dynamically
adjusts the finger threshold based on the noise seen in the system. You should choose the manual mode over
the automatic threshold mode under the following scenarios:
 If the RAM/ROM footprint is smaller than the number of sensors it must support.
 Designs that require precisely adjusted sensor finger thresholds.
 Designs that need to be operated under noisy conditions.
If manual threshold setting mode is used, then to complete the tuning process you must set the finger threshold as
well. Monitor the sensor signal baSnsSignal. Determine 80 percent of its maximum value and this value is the finger
threshold. In the example shown in Figure 4-6 it is nearly 100 counts.