Electronic Parts

Discrete Components

Mechanical Switch Types

Mechanical switches use moving conductive contacts to make, break, or redirect an electrical connection. The part a person touches—a lever, rocker, slider, button, knob, or tiny actuator—usually tells you the physical style of the switch. The internal contact arrangement is described separately.

Toggle switches

A toggle switch is operated by a small lever. Many toggle switches remain in the position selected, although momentary versions spring back when released. They are commonly made as SPST, SPDT, DPST, and DPDT switches and are often used where a clear, positive mechanical action is desirable. A three-position toggle may be marked ON-OFF-ON, ON-ON-ON, or with a momentary position shown in parentheses, such as ON-OFF-(ON). The marking describes the electrical action, not merely the lever position.

Rocker switches

A rocker switch pivots back and forth instead of using a protruding lever. Rockers are common on equipment power panels because the actuator can be broad, easy to label, and nearly flush with the panel. Illuminated versions may contain a lamp or LED in the rocker.

Pushbutton switches

Pushbuttons may be momentary, changing state only while pressed, or latching, remaining in the new state until pressed again or released by another action. A doorbell button is a familiar normally-open momentary switch. Emergency-stop and interlock circuits often make use of normally-closed contacts so an open wire can also be detected as a fault. Pushbuttons may contain one contact block or several mechanically linked blocks, so one button can operate NO and NC circuits at the same time.

Slide switches

A slide switch moves a small knob or tab along a straight path. Slide switches are common on small electronic equipment and circuit boards. The visible position of the slider often provides a useful indication of the selected circuit state.

Rotary switches

A rotary switch selects contacts as a shaft is turned. Some rotary switches simply choose one of several positions. Others contain several electrically separate sections, often called decks, wafers, or poles, all operated by the same shaft. This allows many signal paths to change at exactly the same time.

A single-pole rotary selector commonly has one common or wiper contact and several stationary contacts arranged around it. Turning the shaft connects the common to position 1, 2, 3, and so on. Multi-pole versions repeat that arrangement for several independent circuits. A two-position rotary switch can also be built from many SPDT sections mechanically ganged together. Electrically, twelve ganged SPDT sections operated by one two-position shaft can be described as a 12PDT switch.

Why use a heavily ganged rotary switch?

Sometimes an entire group of signal paths must be rerouted at once. One real-world example is a six-channel guitar pickup system built by the author. A rotary switch containing twelve ganged SPDT sections was used to select whether the six-channel pickup system went to a six-pin direct output connector or through the instrument's onboard controls and stereo output. One knob therefore changed a large collection of connections together.

The number of switch sections does not have to match the number of visible choices. A switch may have only two shaft positions but many poles operating behind the panel.

Rotary-switch details to check

• Number of poles — how many independent circuits are operated.
• Number of positions — how many shaft positions are available.
• Shorting or non-shorting action — make-before-break or break-before-make.
• Stops — some rotary switches use a stop washer or other mechanism to limit positions.
• Contact rating — signal switching and power switching may require very different contacts.
• Shaft, bushing, and mounting — important when the switch is panel mounted.

DIP switches

A DIP switch packages several small individual switches in a body sized for a printed circuit board. Each section normally provides one binary choice, making DIP switches useful for configuration settings, addresses, and option selection. They are mechanically operated switches even though they are often associated with digital circuits.

Key, lever, and selector switches

The same basic contact mechanisms can be fitted with many kinds of actuators. A key switch restricts operation to someone with the proper key; a selector switch may use a knob with two or more maintained positions; and lever switches can provide several directions or contact combinations.

Knife switches

A knife switch uses a visible metal blade that pivots into or out of fixed contacts. It is one of the easiest switch mechanisms to understand because the current path can literally be seen. Knife switches are now more common in demonstrations, older equipment, and specialized power applications than in ordinary small electronics, but the basic make-and-break principle is the same as in enclosed modern switches.

The important distinction

The actuator style does not tell you the complete electrical function. A toggle, rocker, slide, or pushbutton might each be SPST, SPDT, DPDT, momentary, maintained, normally open, or normally closed depending on its design. Always read the switch's contact description and ratings rather than identifying it only by appearance.

Next: poles, throws, NO/NC contacts, symbols, and ratings.