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components

Capacitive Touch Slider

Introduction​

Capacitive touch sliders are user interface elements that detect finger position along a linear set of electrodes. They are commonly used in consumer electronics for volume control, brightness adjustment, and other continuous input.

In tscircuit, you can create a capacitive touch slider using a series of smtpad elements with the solverMask property. The solverMask property allows you to mark pads that should be considered as part of the slider for routing and solver purposes.

Prerequisites​

  • Basic understanding of tscircuit components and PCB layout.
  • Familiarity with smtpad element and its properties.

Creating a Simple Capacitive Touch Slider​

A capacitive touch slider consists of multiple adjacent pads arranged in a line. Each pad is an smtpad with a solverMask set to true (or a specific mask value). The pads can be any shape (rectangular, circular, etc.) and should be placed close together to form a continuous sensing area.

Example: Linear Slider with Rectangular Pads​

The following example creates a slider with five rectangular pads:

import { Board, smtpad } from "tscircuit"

const CapacitiveTouchSlider = () => (
  <board width="50mm" height="20mm">
    {/* Pad 1 */}
    <smtpad
      shape="rect"
      width="2mm"
      height="5mm"
      x="-8mm"
      y="0mm"
      layer="top"
      solverMask={true}
    />
    {/* Pad 2 */}
    <smtpad
      shape="rect"
      width="2mm"
      height="5mm"
      x="-4mm"
      y="0mm"
      layer="top"
      solverMask={true}
    />
    {/* Pad 3 */}
    <smtpad
      shape="rect"
      width="2mm"
      height="5mm"
      x="0mm"
      y="0mm"
      layer="top"
      solverMask={true}
    />
    {/* Pad 4 */}
    <smtpad
      shape="rect"
      width="2mm"
      height="5mm"
      x="4mm"
      y="0mm"
      layer="top"
      solverMask={true}
    />
    {/* Pad 5 */}
    <smtpad
      shape="rect"
      width="2mm"
      height="5mm"
      x="8mm"
      y="0mm"
      layer="top"
      solverMask={true}
    />
  </board>
)

Using Different Shapes​

You can also use circular pads for a different look and feel:

<smtpad
  shape="circle"
  radius="1.5mm"
  x="-8mm"
  y="0mm"
  layer="top"
  solverMask={true}
/>

Connecting to a Microcontroller​

Each pad should be connected to a GPIO pin configured as a capacitive touch input. You can route traces from each pad to a microcontroller footprint. Use the portHints property to assign a net name for each pad, then connect them with trace elements.

<smtpad
  shape="rect"
  width="2mm"
  height="5mm"
  x="-8mm"
  y="0mm"
  layer="top"
  solverMask={true}
  portHints="TOUCH1"
/>
<trace path={[".TOUCH1", ".MCU > .GPIO1"]} />

Advanced Usage​

Solver Mask Values​

The solverMask property can be a boolean (true/false) or potentially a numeric mask value for more complex slider configurations (e.g., interleaved electrodes). When set to true, the pad is included in the solver's consideration for routing and connectivity.

Covering with Solder Mask​

If you want the pads to be covered with solder mask (i.e., not exposed), set coveredWithSolderMask={true}. This is useful for sliders that are placed under a protective overlay.

<smtpad
  shape="rect"
  width="2mm"
  height="5mm"
  x="0mm"
  y="0mm"
  layer="top"
  solverMask={true}
  coveredWithSolderMask={true}
/>

Polygon Pads for Custom Shapes​

For sliders with complex electrode shapes, use the polygon shape:

<smtpad
  shape="polygon"
  points={[
    { x: "-1mm", y: "-2.5mm" },
    { x: "1mm", y: "-2.5mm" },
    { x: "1mm", y: "2.5mm" },
    { x: "-1mm", y: "2.5mm" },
  ]}
  x="0mm"
  y="0mm"
  layer="top"
  solverMask={true}
/>

Design Considerations​

  • Pad spacing: Keep gaps between pads small (e.g., 0.2mm) to ensure continuous sensing.
  • Pad size: Larger pads increase sensitivity but reduce spatial resolution.
  • Layer: Typically placed on the top layer, but can be on bottom if needed.
  • Ground guard: Surround the slider with a ground guard ring to reduce noise.

Conclusion​

Capacitive touch sliders are easy to implement in tscircuit using the smtpad element with the solverMask property. By arranging multiple pads in a line and connecting them to a microcontroller, you can create a robust slider interface for your PCB.

Further Reading​