The ABCs of Capacitive Switches: Terms You Need to Know

Capacitive switches have become an increasingly popular alternative to mechanical switches. They are touch switches that, like other touch switches, don’t contain any moving parts. Capacitive switches leverage a touch-based operation. Touching the interface on a capacitive switch will open or close its circuit. While capacitive switches have a relatively simple design, though, you may encounter some otherwise unfamiliar terms when shopping for them.

Overlay

All capacitive switches have an overlay. It’s the uppermost layer that features the keys, legends or other graphics. Overlays for capacitive switches are made of a nonconductive material. Some of the most common materials used in their construction include plastic and glass.

Dielectric Constant

What is dielectric constant exactly? Also known as relative permittivity, it’s the factor by which an electrical field between a series of charges changes. The factor may increase or decrease. As the dielectric constant changes, capacitive switches are able to detect the presence of a conductive object.

Flexible Printed Circuit

All capacitive switches feature a circuit. While some of them have a traditional rigid circuit, though, others have a Flexible Printed Circuit (FPC). An FPC is a type of circuit-controlling device that leverages a flexible base layer. FPCs can flex and bend without breaking. Their flexible characteristics make them ideal for use in small electronics. You can find capacitive switches with traditional rigid circuits, and you can find them with FPCs.

Embossing

You may encounter the term “embossing” when shopping for capacitive switches. Embossing is a finishing process. It involves changing the shape of an otherwise flat surface. Rather than featuring a flat and smooth surface, capacitive switches can be designed with a raised or textured surface. The finishing process for creating these textured surfaces is embossing.

Backlighting

Backlighting is available for capacitive switches. It consists of a lighting system that’s designed to illuminate the capacitive switch from behind. Backlighting is available with or without light guides. Backlighting systems are responsible for producing light, whereas light guides are responsible for distributing this light, thereby preventing bright or dark spots.

Electrode

All capacitive switches have an electrode. An electrode is nothing more than a conductor. It’s designed to conduct electricity, meaning an electrical current can travel through the electrode with little or no resistance. Capacitive switches feature an electrode behind the nonconductive overlay. When turned on, capacitive switches will apply a charge to the electrode while detecting changes in capacitance. Any contact with a conductive object, such as a bare finger, will result in a change in capacitance. As the capacitance changes, the capacitive switch will then open or close its circuit.