CapSense Performance Tuning with User Modules
CY8C20xx7/S CapSense
®
Design Guide
Doc. No. 001-78329 Rev. *E
40
4.2.11 Set High-Level Parameters
The following recommendations are a starting place for selecting the optimal parameter settings:
Finger Threshold
: Set to 80 percent of raw counts with sensor ON
Noise Threshold
: Set to 40 percent of raw counts with sensor OFF
Negative Noise Threshold
: Set equal to noise threshold
Baseline Update Threshold
: Set to two times noise threshold
Hysteresis
: Set to 10 percent of raw counts with sensor ON
Low Baseline Reset
: Set to 50
Sensors Autoreset
: Based on design requirements
Debounce
: Based on design requirements
4.3 Using the SmartSense_EMCPLUS User Module
SmartSense_EMCPLUS allows you to create a CapSense design that requires no tuning, as long as the sensor
parasitic capacitance is in the range from 5 pF to 45 pF with a minimum 0.1-pF finger touch. You can create a
SmartSense_EMCPLUS design by using the SmartSense_EMCPLUS User Module in PSoC Designer 5.1 or higher
versions. This section also shows you how to migrate an existing CSD CapSense design to
SmartSense_EMC_PLUS.
4.3.1 Guidelines for SmartSense_EMC_PLUS
Follow these guidelines when using the SmartSense_EMCPLUS User Module in an application:
SmartSense_EMCPLUS requires that the capacitive user interface design follows the layout and system design
best practices documented in the
section.
All of the CSD/CSDPLUS UM parameters (such as I
DAC
value, prescaler period, clock divider, scan speed, and
resolution) are determined at runtime by the SmartSense_EMCPLUS User Module. You should not use APIs that
modify these CSD parameters in firmware, unless you know exactly what effect it has in your design.
To migrate an existing design from CSD/CSDPLUS to SmartSense_EMC_PLUS:
Ensure that all APIs that set or modify the CSD/CSDPLUS parameters are first removed from the program.
Ensure that the parasitic capacitance of all CapSense sensors in the design is between 5 pF and 45 pF over
environmental and PCB production process variations.
Make sure recommended C
MOD
capacitor (X7R, 2.2-nF, and voltage rating more than 5 V) is connected to
the C
MOD
port pin selected in the user module wizard.
4.3.2 Understanding the Difference
The differences between the SmartSense_EMCPLUS User Module and the standard CSD/CSDPLUS User Module
are:
The SmartSense_EMCPLUS User Module supports the same APIs that a standard CSD/CSDPLUS User
Module supports. Thus, no change is required in placing, configuring, starting, or calling other APIs except the
User Module instance name.
There is no need to set any User Module parameters for tuning, as all the parameters related to tuning are
automatically set at runtime by the SmartSense_EMCPLUS User Module.
The C
MOD
capacitor value is restricted to 2.2 nF
.
Use of an X7R or NPO capacitor with a voltage rating higher
than 5 V is recommended in all CapSense applications.
The SmartSense_EMCPLUS algorithm maintains the signal SNR of each sensor between 5:1 and 11:1 to ensure
robust CapSense operation while maximizing performance.
The scanning time of the SmartSense_EMCPLUS User Module is restricted by the algorithm to be between
410 µs and 2.8 ms per sensor in 24-MHz operating mode, based on the parasitic capacitance of the sensor.
