Switch mechanisms:Slide switches and Push-button switches

Slide switches

The mechanism of a slide switch does not permit any form of snap action:

the speed of making or breaking depends purely on the operator, and there is nothing to stop a switch being placed and left in a mid-way position. Such switches are therefore specified more for use in signal circuits, and in supply circuits that use low-voltage AC or DC. The main advantages of using a slide switch are that the contacts usually have a wiping action that ensures clean surfaces, and that the contact pressure can be quite high without making the switch action difficult. Fastening can be achieved using bolts through lugs, PCB mounting or clips. Single slide switches are becoming a rare sight in electronics equipment; they are being replaced by DIL pattern switches (which are of the slide pattern) for signal voltages, and by miniature rocker switches for supply voltage use.

Push-button switches

Switch principles -0875

Push-button switches challenge the range of toggle switches for variety, although many push-button types are intended purely for signal uses. The two basic types of push-button switch are the momentary-action and alternate-action types. The internal construction of a momentary-action switch (Figure ll.6) demonstrates the principles. The moving contact is held on the shaft that is actuated by the button, and the contact is made (in this example) for as long as the button is pushed. Releasing the button allows the main spring to separate the contacts, subject to the range of travel of any internal spring that is used to buffer the moving contact from the shaft. This type of momentary-use switch can be of push-to-make or push-to-break varieties.

The other basic type is the alternate-action type. In this version, pushing the button will reverse the effect of the previous push, switching either on or off. The mechanism is usually rotary and permits only fairly small contact pressures, so these switches are not intended for high current uses. For the mains switching versions, 250 V and 3 A is a typical rating, although higher current ratings are available. The term latching is often used of the alternate mechanism, but latching has a specialized meaning when applied to a push-button switch. A latching push-button switch will allow the button position to indicate whether the switch is on or off, for example by having the button fully out when the switch is off, and partly in when the switch is on. The mechanism of a latching switch is basically that of the alternate type, but with the push button connected to the internal mechanism rather than simply pushing.

Push-button switches of either basic type are available with solder lugs or pins, or PCB mountings, but seldom with snap-on receptacles. Like rocker switches, many types of push-button switches are available with illuminated buttons in a variety of shapes and colours. The illumination is usually by miniature filament bulbs that will require a low-voltage supply, rather than by the neon which is used for rocker switch types.

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