Short answer: for very light touch (near-zero force), use a capacitive touch sensor. If you need to measure a gentle press (small force) instead of just “touch/no-touch,” use a thin force sensor (FSR or piezoresistive). Here’s the quick chooser:
Pick the right sensor for “light touch”
What not to pick for light touch
- Resistive touchscreens / tact switches: typically need tens of grams of force—not “feather touch.”
- Load cells/strain gauges: super accurate but bulky and overkill unless you truly need calibrated grams.
Starter circuits (quick recipes)
- Capacitive touch (one pad): TTP223 → VCC 3.3–5 V, one copper pad as electrode, OUT to MCU pin. Works through a few mm of plastic; avoid long wires or add series R (≈1 kΩ) and ground guard if noisy.
- FSR/FlexiForce (analog force): Voltage divider into ADC. For very light forces, use an op-amp (transimpedance or gain stage), add temperature & time calibration; expect nonlinearity.
- Piezo tap sensor: Piezo → series resistor (≈1 kΩ) + clamp diodes to protect MCU; 1–10 MΩ bleed to ground; read with ADC/compares for tap detection.
Quick recommendations by use case
- Touch button on a plastic panel: Capacitive (AT42QT1010/TTP223 or a multi-channel IC).
- Soft “press to dim” on a wearable or foam: FlexiForce (op-amp + ADC).
- Detect a light knock on a surface/enclosure: Piezo film strip to ADC/interrupt.
- Wake-on-approach behind glass: Capacitive proximity or IR ToF.
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