Toggle and Push-Button Switches
by Cole Dudley
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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,
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-
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.
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
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
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 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.
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 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.
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 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
Croft, Terrel. American Electrician's Handbook: Fourteenth Edition. McGraw-Hill
Horowitz, Paul. Hill, Winfield. The Art of Electronics. Cambridge University Press.
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