Building a Capacitive Touch Sensor with tscircuit

Overview

Capacitive touch sensors replace mechanical buttons with copper shapes that detect when a finger changes their electric field. In this tutorial you will:

• Draw a capacitive electrode using polygon surface-mount pads.
• Connect the electrode to a capacitive touch controller.
• Route the traces, ground reference, and LED indicator for feedback.
• Simulate the PCB stackup with tscircuit before ordering the board.

The finished design exposes a responsive touch pad that lights an LED when it is activated.

Bill of Materials

Quantity	Component	Notes
1	AT42QT1010 single-channel touch controller	Any capacitive-touch controller with a single key works.
1	3.3 V regulator (or 5 V source if available)	Provides a clean supply for the controller.
1	0603 LED + series resistor	Indicates when the sensor fires.
1	Polygon copper electrode	Created directly on the PCB.
Misc	Programming header, decoupling capacitors, optional guard ring	Follow the controller datasheet.

Step 1 – Define the Electrode Footprint

We can create a smooth, finger-sized electrode by combining polygon pads inside a reusable footprint. The code below mirrors the three overlapping electrodes used in the board preview image.

const PolygonSmtpads = (props: { name: string }) => {
  return (
    <chip
      {...props}
      footprint={
        <footprint>
          <smtpad
            shape="polygon"
            layer="top"
            portHints={["sense"]}
            points={[
              { x: -4.5, y: 2 },
              { x: -2.2, y: 2 },
              { x: -0.4, y: 0 },
              { x: -2.2, y: -2 },
              { x: -4.5, y: -2 },
            ]}
          />

          <smtpad
            shape="polygon"
            layer="top"
            portHints={["sense"]}
            points={[
              { x: -1.8, y: 2 },
              { x: 1.8, y: 2 },
              { x: 3.6, y: 0 },
              { x: 1.8, y: -2 },
              { x: -1.8, y: -2 },
              { x: 0, y: 0 },
            ]}
          />

          <smtpad
            shape="polygon"
            layer="top"
            portHints={["sense"]}
            points={[
              { x: 2.2, y: 2 },
              { x: 6, y: 2 },
              { x: 6, y: -2 },
              { x: 2.2, y: -2 },
              { x: 4, y: 0 },
            ]}
          />
        </footprint>
      }
    />
  )
}

Step 2 – Place the Board Elements

Use the custom electrode on a board and add a dedicated touch controller. The snippet below lays out the electrode, an AT42QT1010 controller, and an LED with minimal routing.

Step 3 – Route Guard and Reference Copper

Capacitive sensors are sensitive to noise. Surround the electrode with a grounded copper pour on the bottom layer and keep the sensor trace short. If your controller supports it, add a driven shield trace between the sensor and noisy signals.

Step 4 – Tune the Sensor

After fabricating the PCB:

1. Power the circuit and measure the idle capacitance reported by the controller.
2. Adjust sensitivity or debounce registers until a light finger touch reliably toggles the LED.
3. Test with different enclosures or overlays (e.g., acrylic, wood). Increase electrode size if the overlay is thick.

Visualizing the Electrode Layout

The board rendering below shows how the three polygon pads create a wide, tapered sensor that guides the user toward the center.

Next Steps

• Add multiple electrodes by duplicating PolygonSmtpads and using a multi-channel controller.
• Experiment with interdigitated shapes for slider widgets.
• Integrate the sensor into a custom enclosure for touch-based user interfaces.