Toggle and Push-Button Switches

Introduction

The ability to control an electric current is the foundation that modern electronics is built upon. It's not difficult to create a flow of electricity, but to harness that power and transform it into performing a practical function requires the use of circuits and components. One of the most fundamental components is a common passive electromechanical device known as a switch. These mundane but important devices are are found in most electronic equipment, and are widespread in the art of case modification and computer customization. Switches can be found in many types and configurations; some common switch types are toggle, push-button, rotary, rotary, reed, proximity, Hall-effect, momentary, pressure, rocker, magnetic, dip, slide, thumbwheel, keylock, etc. A switch is a device for making, breaking, or changing connections in an electric circuit under the conditions of a load for which it is rated.

Classification of Switches

Switches may be classified in several different ways:

1.) According to number of poles (SP, DP, 3P, etc.)
2.) According to number of closed positions (Single-throw, double-throw)
3.) Type of contact (Knife blade, butt-contact, mercury)
4.) According to number of breaks (Single or double)
5.) According to method of insulation (air-break, oil immersed)
6.) According to method of operation [Operating Force (Manual, Magnetic, Motor), Mechanism (Lever, dial, drum, snap)]
7.) According to speed of operation (quick-break, quick-make, slow-break)
8.) According to enclosure (open, enclosed)
9.) According to protection provided to circuits or equipment
10.) Type of service (power switches, wiring switches, control switches, instrumental switches)

Sorting through the vernacular describing switches and electrical components can be a daunting task; however, when speaking in terms of case modification, one only needs to be concerned about the polarity and number of closed positions.

A pole of a switch is that part of a switch which is used to make (or break) a connection and which is electrically insulated from other contact-making parts. A single-pole switch will make or break connections in only one conductor or leg of a circuit; a two-pole switch, in two legs, etc.

Electrical circuits are always either open (off) or closed (on). Switches are available in on-off (single-throw/closed-open) configuration or on-off-on (double-throw/closed-open- closed) configuration.

Push-button momentary contact switches operate differently compared to toggle switches. Momentary contact switches are normally closed (N.C.) or normally open (N.O.). This type of switch cannot open and close a circuit, but rather, open or close a circuit. To illustrate this type of action, visualize that the button of the switch must continually be pushed to perform the function (either momentary open or momentary closed). For example, if a fan is hooked up to a normally open switch, then whenever the button is pushed, the circuit will be closed and the fan will spin. When pressure on the button is relieved, then the fan will no longer spin. The opposite is true with a normally closed switch; the fan would normally spin, but once the button is pushed, it would stop spinning; the fan would start spinning once pressure on the button is relieved.

A computer uses this type of switch to power the machine on and off (assuming it is an ATX computer). A computer uses a normally open (N.O.) switch that when activated closes the circuit sending a signal to the motherboard. The motherboard handles on-off activity and sends a signal through the ATX cable to the power supply turning on the machine. The on-off switch is used in conjunction with the computer's electronics to handle shutting the machine off and turning it on.

Electrical Terms

Electricity: Electricity can neither be created nor destroyed. It can, however, be forced to move and thus transmit power or produce electrical energy. A quantity of electricity is measured in Coulombs (C). A coulomb of electricity comprises of approximately 6.0*10^18 electrons. Charge can be found by multiplying current by time.

Current: Current is measured in amperes and is the rate of flow of electricity. Current is merely a shifting of electricity through a conductor, generally electrons. Current can be found by a variety of equations, one of the most common being Ohm's Law Resistance=Voltage/Current.

EMF (electromotive force) or Voltage: Voltage is the force or pressure that makes electrons move throughout a circuit. This is also known as the electric potential difference. Voltage can be found using electric power equations (P=VI) or Ohm's Law (R=V/I).

Resistance: Resistance is the name given to the opposition incurred in a circuit. This resistance converts electrical energy into heat in accordance to the formula W=I^2*R. All materials exert some form of resistance when a current is pushed through. Conditions that change the resistance include: cross-sectional area, material, temperature, and length. Resistance is measured in Ohm's, and can also be found using Ohm's Law. A resistor is an object having resistance inserted into a circuit to provide resistance. Rheostats are arranged so that the resistance can be varied.

Power: Power is measured in watts and can be found my multiplying the current by the voltage. Power goes into heat, mechanical work, radiated energy, or stored energy.

These terms will come in useful when performing case modifications because many items have current, voltage, and power restrictions.

Toggle Switches

Toggle switches are the most familiar switches associated with computer customization. The simple toggle switch is available in various configurations depending on the number of poles and switching positions. This illustration using knife switches might give one a better understanding of how the terminals interact and work.

SPST

These switches are simply used for turning something on and off. They are handy for lighting, or complicated baybuses that need an on-off switch. This type of switch simply allows one to change the circuit between open and closed.

SPDT

SPDT switches are useful if you want to supply some instrument with two different voltages (such as a fan) or if you want a certain voltage to be directed at one item (maybe a fan) at one time, then once the switch is flipped the voltage is directed at another item. This type of switch allows one to switch between two different types of closed circuits and an open circuit.

DPST

A Double-pole Single-throw switch is simply two SPST switches together. It allows you to switch two separate circuits on and off at once. This would be useful if you didn't want to use more than one switch for two items. 3PST, 4PST, and 5PST switches can also be found that work the same way.

DPDT

DPDT switches have six terminals and allow one to switch poles between two different circuits. These may be useful for dual voltage baybuses as well as changing voltages in complicated circuits.

Momentary Contact/Push-Button Switches

Normally open switches are the type used to turn one's computer on and off. When the switch is pressed, the circuit becomes closed and functions. I always think of a car with nitrous injection capabilities; push a button and unleash 150 more horsepower.

Normally closed switches perform just the opposite function. When the switch is pressed, the circuit becomes open. One may use this type of switch to turn a fan off that is inconveniently located while opening a case.

Push button switches can also be found in SPST configurations and are a cool alternative to toggle switches. These type of switches work so that when the button is pressed it remains pressed until pressed again.

Conclusion and Final Thoughts

Switches, while often mundane and boring, are some of the most useful, common, and versatile electrical components. The fun doesn't stop with toggle and push-button switches: several other types are readily available for modification. One such switch is a reed switch, which Dr. Michael wrote an article about. Relays, or electronically controlled switches, are a barrel of fun and could find a home in case modification. Potentiometers are quite common in the current crop of case modification products (variable speed fan controllers, volume controllers, etc.). The majority of case modifications involving electricity will need some sort of switch, so I hope this article will answer some of your questions. If you have any further questions or comments, let me know.

References

Croft, Terrel. American Electrician's Handbook: Fourteenth Edition. McGraw-Hill Handbooks. 2002.
Horowitz, Paul. Hill, Winfield. The Art of Electronics. Cambridge University Press. 1980.