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PSoC 4 MCU

nkin_2927171
New Contributor II

hi

We develop one touch PCB.

My controller is CY8C4245AXI-483

Which have 4 x 6 matrix touch switch.

and 2 Normal touch switch.

our requirement is 6 mm overlay thickness.

I solder one PCB and develop code.

all working fine without overlay.

same thickness overlay in both touch (Matrix and normal touch )

both touch pad have same size.

after put overlay on PCB,normal touch pad work fine but Matrix touch is not working.

Is that right ,Matrix touch is not working and simple touch button is working even if both have same radius ???

designed attached.

0 Likes
1 Solution
ShanmathiN_06
Employee

Hi,

This is expected scenario. Since all the buttons in a single row are connected together, the parasitic capacitance of that particular row would be higher. Same theory applies for column too.

Whereas, in single buttons, the parasitic capacitance of only that button is included. Hence, the Cp is lesser which would result in higher sensitivity and hence, detects touch.

In matrix buttons, Cp is higher for row and column sensors and hence, reduces sensitivity.

Are you using SmartSense? If yes, please check if the parasitic capacitance is withing the Cp limits supported by SmartSense.

If you are using manual tuning, increase the resolution.

Also, what is the dielectric constant of your overlay? Higher the constant, higher is the sensitivity.

Thanks,
Shanmathi

View solution in original post

3 Replies
ShanmathiN_06
Employee

Hi,

This is expected scenario. Since all the buttons in a single row are connected together, the parasitic capacitance of that particular row would be higher. Same theory applies for column too.

Whereas, in single buttons, the parasitic capacitance of only that button is included. Hence, the Cp is lesser which would result in higher sensitivity and hence, detects touch.

In matrix buttons, Cp is higher for row and column sensors and hence, reduces sensitivity.

Are you using SmartSense? If yes, please check if the parasitic capacitance is withing the Cp limits supported by SmartSense.

If you are using manual tuning, increase the resolution.

Also, what is the dielectric constant of your overlay? Higher the constant, higher is the sensitivity.

Thanks,
Shanmathi

View solution in original post

nkin_2927171
New Contributor II

OK

as per your review.

I change my design.

all are in single button now.

I use SmartSense in my code.

I don't know my dielectric constant ,but i generally used 2 mm acrylic + 3mm glass. (work fine video attached)

I start my new design.

Would you review on that ?

right now only right side 12 button design ,same mirror design on left side i will do.

My controller is CY8C4245AXI-483

and also whats gape you prefer between cap-button to GND ??

1 mm OR 2 mm ??

designed attached.

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ShanmathiN_06
Employee

Hi,

You can refer toTable 7-1 of https://www.cypress.com/file/46081/download to know about the dielectric constant. Higher the better. Glass has high dielectric constant. So, maybe you could use only glass.

You can have 2 mm gap between button and Gnd hatch as this will reduce Cp (parasitic capacitance). Ensure that you Cp is within the limits specified by SmartSense.

Thanks,
Shanmathi