Does anybody know how many capacitive keys (CSD) I can use on CY8C4014LQI-421 ?
the part number you have mentioned is a 16-QFN.
It has 9 Capsense pins capable of doing 9 Capacitive keys.
1 pin will go for CMOD.
So, you can do 8 capacitive keys.
if you need shield, then 1 pin will be gone for CTANK and 1 for Shield.
So, you can have 6 Capacitive keys.
I assume you want buttons when i say keys, if you want Sliders, then the calculation will be different.
pls let me know your requirements to help better.
Please note that Ctank is not always needed, even if shield is used. It is only needed when the shield capacitance is very high. For more information on this, please refer to the Capsense design guide for the respective device.
Design guide -
http://www.cypress.com/?rID=78578 PSoC® 4 CapSense® Design Guide