Capsense button size design question

[gryfin_chen]

I would like to ask some technical questions about CapSense detection

we want to make a small Button on the inside of the ring to detect whether the ring is wear,but based on the design manual, it is recommended that the size diameter should not be less than 5mm,and the signal-to-noise ratio must be 1cm for the shielding layer,not sure if such a design direction is recommended.

or suggest that the method of proximity sensing can provide us with a new Idea

[Arpit_S · Accepted solution]

Hi @gryfin_chen ,

One thing that can be done is, you can use CapSense Sensor beneath the ring, Make it as per the ring's dimension and then calculate the Cp of the sensor. The CapSense sensor Cp has to be in 5 pF – 200 pF (Fourth Gen) and 2 pF - 200 pF (For Fifth Gen).  You can refer to https://github.com/Infineon/mtb-example-psoc4-msc-capsense-csd-button-tuning README.md Stage 2: Measure the Parasitic capacitance (Cp) to see how to measure Cp

If Sensor Cp is less than the range then you can use a 5pF capacitor on a GPIO and then Gang the Sensor and the capacitor together, this will result in net Cp greater than 5pF. You can refer to Page 143 https://www.infineon.com/dgdl/Infineon-AN85951_PSoC_4_and_PSoC_6_MCU_CapSense_Design_Guide-Applicati... 

Can you guide me about the material of the ring? If it is metal, this will not work. As in this case, the whole ring will become as sensor and touching the ring will be same as that of wearing the ring. Moreover, CapSense Design considerations won't be followed.

Thanks!
Kind regards

Arpit Srivastav