Touch button and slider design

[ypkdani]

Hello all,

i have a problem with my first design of a touch button and a slider on a 4layer pcb (top-layer2-layer1-bottom) using a STM32L162 with its peripheralTouch sensing. As you can see from the image i have design the button and the slider with a shield to increase the noise immunity. My problem is a) the sensitivity that is not enough b) reduce the noise from the leds on the bottom that light up the device.
Up the pcb i have 2mm of plastic so i need to increase the sensitivity of the buttons for detect the slider or the button press. My ideas are:

• separe the shield for the button and the slider that now is the same
• to increase the diameter of the button copper from 1.5mm to 3mm and the button shield from 1.5mm to 4mm.
• increase the gnd plane on the bottom where there are the leds for reduce the noise from these
• increase the width of the slider from 1cm to 1,5cm and the shield from 1,2 to 2cm if possible

In the image you can see the signal from the button, or slider, from the channel 1 and the shield signal from the channel 2.

Do you have other suggestions??
Thanks

[Docara]

Hi ypkdani,

Whilst I cannot give you a specific answer, I can give you a general open ended response.

I'm also embarking on my first design with touch. The one think you MUST DO is read, read and read some more the datasheets and the applications notes pertaining to the manufacturer. All the info is there.

My latest favourite is Cypress and their CY8CMBR3116 (CY8CMBR3xxx) range of CapSense. They also supply free software that you can configure 'things' if you have slightly messed up your design via the I2C bus. I have an ongoing forum question concerning if any 'USB TO I2C' boards will work with their software (EZ-Click 2.0) or you have to buy there own one --- mmm let me think what they'll say!!!!!!

Lastly, I am struggling to find an EDA (free) program that will do a hatched ground plane around the pads using the copper fill/pour tools. You will probably have to do it in Inkscape and import, KiCad also doesn't import graphics onto a copper layer you have to use its "Bitmap2Componen" utility (somehow)