Touch Sensor
Reports a digital high or analog count when a finger or conductive object touches (or hovers near) a sensing pad. Multi-touch capable devices use a grid of electrodes scanned in turn.
Capacitive: a self-capacitance or mutual-capacitance measurement detects the change in stored charge when a finger (~100 pF to ground) is near the electrode. Sigma-delta or charge-transfer front ends digitize the change.
In plain terms
A small antenna that knows when your finger comes near, because your finger's grounded body steals away some of its electric field.
Why designers use it
- Phone, tablet, and laptop touchscreens.
- Touch buttons on appliances (microwave panels).
- Slider controls on audio equipment.
- Proximity detection for wake-on-approach.
Best for
- Touchscreens
- Appliance buttons
- Sliders
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- Wet or gloved hands without compensation.
- Through thick metal panels — the field is shielded.
Common mistakes
- Forgetting that ungrounded floating PCBs reduce sensitivity.
- Skipping shield electrodes and getting noise from nearby switching converters.
Where you will find it
- Apple iPhone (2007) brought projected-capacitive multi-touch to mass-market phones.
- TI MSP430 / FDC2114 and Microchip mTouch-class libraries are standard for capacitive buttons.
- Kitchen appliance front panels (cooktops, microwaves) increasingly use cap-touch glass.
A short history
Capacitive touch dates to E.A. Johnson's 1965 work at the Royal Radar Establishment. Bent Stumpe at CERN built one of the first capacitive touchscreens in 1973. FingerWorks's multi-touch tech (acquired by Apple in 2005) became the iPhone's multi-touch system.