Creating Custom Electrodes

What makes a good electrode?

A Touch Board electrode is any conductive material connected to one of the 12 pads. The MPR121 doesn’t care about material, shape, or size — it measures capacitance change. But physical choices affect reliability, aesthetics, and sensitivity.

Good electrodes have:

• Low resistance to the Touch Board — under 1 MΩ; ideally under 100 kΩ
• Stable physical connection — won’t detach during use
• Appropriate size — large enough to detect a touch, small enough to avoid cross-coupling
• Good isolation from adjacent electrodes — at least 5mm of non-conductive material between traces

Material options

1. Copper tape

Best for: paper projects, prototyping, clean straight lines, soldering

Self-adhesive copper tape (3M 1181 or similar) is highly conductive, easy to cut, and can be soldered. Available in widths from 3mm to 50mm.

Application tips:

• Press firmly — the adhesive needs full contact to conduct at joints
• Fold around corners rather than cutting — cuts break the tape
• Burnish with a flat tool to ensure adhesion
• Solder connections rather than relying on pressure for permanent installs

2. Aluminium foil / kitchen foil

Best for: quick prototypes, classroom projects, temporary installs

Lower conductivity than copper but works well. Cannot be soldered — connect with crocodile clips or conductive tape.

3. Electric Paint

Best for: curved surfaces, organic shapes, painted artwork, fabric

Covered in detail in Starter article 7. Key points for electrodes: use multiple thick layers, and check resistance with a multimeter.

4. Conductive fabric and e-textiles

Best for: wearables, soft interfaces, fabric art

Options:

• Shieldex Carbonflexx — lightweight, washable, solderable
• LessEMF silver-coated nylon — very low resistance, less washable
• Plug and Wear conductive fabric — easy to sew, designed for e-textiles

Attach to Touch Board pads with crocodile clips or sew a conductive thread connection. The fabric itself is the electrode — no paint needed.

5. Bare wire / tinned copper wire

Best for: hidden electrodes inside objects, 3D electrode shapes

Soldering hook-up wire directly to the Touch Board pad and then shaping or hiding the wire. Works through thin material (paper, thin leather, thin plastic).

6. Fruit, plants, and water

Yes, these work. Plants and fruit are about 70% water, making them reasonable conductors. Wire one end into a pot plant or piece of fruit and the other to a Touch Board electrode. Touch the plant to trigger a sound.

Through-material sensing

The MPR121 can detect touch through non-conductive material if it’s thin enough:

To sense through material: place the electrode behind or inside the material, set higher sensitivity (lower touch threshold). The finger’s capacitance couples through the insulating layer.

// More sensitive settings for through-material sensing
MPR121.setTouchThreshold(15);    // default is 40
MPR121.setReleaseThreshold(8);   // default is 20

Sizing electrodes

A larger electrode has higher resting capacitance. The MPR121’s auto-calibration handles this, but very large electrodes can:

• Saturate the baseline tracking if the size changes quickly (someone grips it)
• Reduce sensitivity to light touch because the noise floor is higher

Rule of thumb:

• Single fingertip touch: 2cm × 2cm minimum
• Full palm touch: can be large (10cm × 10cm) — reduce sensitivity if needed
• Adjacent electrodes: leave at least 5–10mm gap between electrode areas

Connecting electrodes to the Touch Board permanently

For installations that need to last months or years, avoid crocodile clips:

1. Solder wire to a copper tape patch on the electrode side
2. Solder the other end to the Touch Board electrode pad (use a fine tip, flux, low heat)
3. Strain-relief — hot-glue or tape the wire near the connection to prevent it pulling on the solder joint

For removable but more reliable than crocodile clips: pogo pins or spring-loaded test clips.

Key takeaways

• Copper tape is the most versatile electrode material — conductive, adhesive, solderable
• Conductive fabric creates soft, flexible touch areas for wearables
• Through-material sensing works on thin substrates — increase sensitivity (lower thresholds)
• Keep electrode areas at least 5–10mm apart to prevent cross-coupling
• For permanent installations, solder connections and strain-relieve cables
• Plants, fruit, and water all work as electrodes — anything conductive does