Touch switch

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A touch switch is a type of switch that only has to be touched to operate. It is used in many lamps and wall switches that have a metal exterior as well as on public computer terminals.

1 Overview
2 Capacitance touch switch
- 2.1 Uses
3 Resistance touch switch
- 3.1 Uses
4 External links
- 4.1 Example schematics

[edit] Overview

There are two types of switches called touch switches:

Capacitance touch switch

A capacitance switch needs only one electrode to function. The electrode can be placed behind a non-conductive panel made of for example wood, glass or plastic.

Resistance touch switch

A resistance switch needs two electrodes to be physically in contact with something electrically conductive (for example a finger) to operate.

[edit] Capacitance touch switch

A capacitance touch switch works using body capacitance, a property of the human body that gives it great electrical characteristics. The lamp keeps charging and discharging its metal exterior to detect changes in capacitance. When a person touches it, it increases the capacitance and triggers the switch.

Capacitance switches are available commercially as integrated circuits from for example:

Omron: Model B6TS04LT (4 channel) and B6TS08LT (8 channel).
Quantum Research Group: Model QT 113.

[edit] Uses

The capacitance touch switch can be seen at, for example, public computer terminals.

[edit] Resistance touch switch

A resistance touch switch works by lowering the resistance between two pieces of metal. It is thus much simpler in construction compared to the capacitance type switch. Placing one or two fingers across the plates achieves a turn on or closed state. Removing the finger(s) from the metal pieces turns the device off.

One implementation of a resistance touch switch would be two darlington-paired transistors where the base of the first transistor is connected to one of the electrodes.

Also, an N-Channel, enhancement-mode, metal oxide field effect transistor can be used. Its gate can be connected to one of the electrodes and the other electrode through a resistance to a positive voltage.