Touchpads and Touchwheels

Some capacitive sense touch sensors: buttons and touchwheels

Touchpads

Touchpads are capacitive sensing button inputs that consist of a copper pad and (usually) 1M pull-down resistor, both hooked up to a microcontroller GPIO pin. Code on a microcontroller repeatedly charges and times the discharge rate of the pad. The discharge time changes when a finger is close to the pad. This change can be used to detect a button press. The CircuitPython touchio library and the Arduino library TouchyTouch are two ways of using these capacative touch pads

Touchpad boards

• buttons4x0 - Four 11 mm capacitive touch buttons for use with breadboards or in a project

  https://github.com/user-attachments/assets/d40d3ede-4ee4-4309-8d3a-04f324b11f05

  

Touchwheels

These work by using only three capactive touch pads in a specific interleaved geometry and measuring the relative ratio of analog capacitive touch values between the pads to compute a distance along the slider.

Touchwheel boards made so far:

• TouchWheelSAO -- Touchwheel SAO as part of Hackaday Supercon 2024 badge

• touchwheel0 - available on Tindie as a kit!

  

  Similar to an iPod's wheel, touchwheel0 is a 30 mm (0.6") diameter rotary capacitive touch slider that can be used with most any microcontroller. It uses three digital GPIO pins and requires no extra components. The included examples in CircuitPython and Arduino show how to turn the raw capacitive touch readings of the three pins into a linear 0-360º angle measurement.

• picoslidertoy - Available at the picoslidertoy repo

  

Touchwheel Demos:

There are several examples on how to use the touchwheel:

• demo0 - CircuitPython example showing basic concept on touchwheel0

• touchwheel_badgedemo - CircuitPython example for the Hackaday SuperCon 2023 badge (where touchwheel0 PCBs were given away)

• demo_dual - CircuitPython example show two touchwheel0s in use

• more demos coming!

What's in Tindie touchwheel0 kit:

The touchwheel0 kit on Tindie comes with:

• touchwheel0 black PCB
• 4 x 1M 0805 SMD resistors (only three needed, one is a spare)
• 1 x 4-pin pin header

It makes a pretty good "first SMD soldering" exercise as the 0805 resistors are relatively big and not very heat sensitive.

Demo videos:

• demo dual: (click to view on youtube)

  

• demo0:

  https://github.com/todbot/touchwheels/assets/274093/fc2b794f-5dff-42b4-8942-f141de19e4ab

Useful links:

• AN2934 - Capacitive Touch Sensor Design Guide (pdf)
• QTAN007 - Buttons, Sliders and Wheels - Sensor Design Guide (pdf)
• AT02259: QTouch Schematic and Layout Checklist (pdf)
• SLAA891B: Automating Capacitive Touch Sensor PCB layouts with OpenSCAD Ti AppNote (pdf)
• slider generator