Question: How do you calculate the resolution of a capacitive touch sensing application designed using the CY8C21x34 CapSense® CSD?
Resolution is equal to the inverse of sensitivity. Sensitivity is calculated using the following formula:
Counts = Digital capacitance measurement result returned by the User Module
N = Resolution of the User Module
RB = Bleed resistor value
FSW-AVG = Average switching frequency of the sensor
RefVal = Reference value of the User Module
For example, given the following User Module settings:
N = 14
RB = 10 kΩ
FSW-AVG = 375 kHz (Prescaler = 15)
RefVal = 0
Resolution = 0.00543 pF
Note: Although the calculation indicates that a change as small as 0.00543 pF can be detected, raw-count noise limits the use of such high resolution. CapSense is not recommended for measuring absolute capacitances.
Note: The “sensitivity” calculated above is the capacitive measurement module sensitivity, not the system sensitivity to button/sensor activation.