Download Switches Contacts In the simplest case, a switch has two pieces of

Slot Principles I
• Switches
• Buttons
Switches
• Overview
• Used in many devices
• Varying levels of complexity of the switch
• Varying levels of complexity of the assemblies
• Some common types below
Picture by Arnold
Reinhold.
Switches
• Contacts
• In the simplest case, a switch has two pieces of metal
called contacts
• That touch to make a circuit,
• That separate to break the circuit.
• The contact material is chosen for its:
• Resistance to corrosion, because most metals form insulating
oxides that would prevent the switch from working.
• Contact also chosen on the basis of electrical conductivity
• Hardness (resistance to abrasive wear)
• Mechanical strength
• Low cost
• Low toxicity[
Switches
• Contacts
• Sometimes the contacts are plated with noble metals
• They may be designed to wipe against each other to
clean off any contamination
• Nonmetallic conductors, such as conductive plastic, are
sometimes used.
• Actuator
• The moving part that applies the operating force to the
contacts is called the actuator, and may be a toggle or
dolly, a rocker, a push-button or any type of mechanical
linkage (see photo).
Switches
• Contact arrangements
• A pair of contacts is said to be 'closed' when there is no
space between them,
• Allows electricity to flow from one to the other.
• When the contacts are separated by an insulating air gap,
an air space, they are said to be 'open',
• No electricity can flow at typical voltages.
• Switches classified according
• To the arrangement of their contacts in electronics fields
• But electricians in the electrical wiring service business
use different nomenclature,
• such as "one-way", "three-way" and "four-way”
Switches
• Switches Normally Opened/Closed
• Some contacts are normally open (Abbreviated "n.o." or
"no") until closed by operation of the switch
• Others are normally closed ("n.c. or "nc") and opened by
the switch action
• Abbreviations given are commonly used on electronics
diagrams for clarity of operation in assembly, analysis or
troubleshooting
• Changeover switch
• Make-before-break switch contact
• Break-before-make switch contact
Switches
• Changeover switch
• Which type is used could be important
• If for example, the switch selects two different power sources
instead of switching circuit loads
• Or the circuit load will not and cannot tolerate any interruption
in applied power.
• pole and throw are also used to describe
switch contact variations
• A pole
• Set of contacts, the switch's electrical terminals that are
connected to and belong to a single circuit, usually a load.
• A throw
• One of two or more positions that the switch can adopt
Switches
• pole and throw are also used to describe
switch contact variations
• A throw
• Which normally, but not always correspond to the number
positions the switch handle or rotor can take when connecting
between the common lead of the switch and a pole or poles
• A throw position which connects no terminals (poles), has a mismatch between positions and positions which connect terminals
• But are quite useful to turn things "Off" or for example,
alternatively select between two scaled modes of operation. (e.g.
Bright illumination, moderate illumination, no illumination.)
• Abbreviations for the types of switch in electronics
• Such as
• "single-pole, single-throw" (SPST) (the simplest type, "on or off“)
Switches
• pole and throw are also used to describe
switch contact variations
• Abbreviations for the types of switch in electronics
• Such as
• "single-pole, double-throw" (SPDT), connecting either of two
terminals to the common terminal
• In electrical power wiring (i.e. House and building wiring by
electricians) names generally involving the suffixed word "way" are used
• Types
• SPST
• Single pole, single throw
• A simple on-off switch: Example is a light switch
Switches
• Types
• SPDT
• Single pole, double throw
• A simple changeover switch: C (COM, Common) is connected
to L1 or to L2
• DPST
• Double pole, single throw
• Equivalent to two SPST switches
controlled by a single mechanism
• DPDT
• Double pole, double throw
• Equivalent to two SPDT switches
controlled by a single mechanism:
Switches
• Contact bounce
• Also called chatter
• Common problem with mechanical switches and relays
• Switch and relay contacts are usually made of springy metals
• They are forced into contact by an actuator.
• When the contacts strike together, their momentum and
elasticity act together to cause bounce.
• The result is a rapidly pulsed electrical current instead of a clean
transition from zero to full current.
• The waveform is then further modified by the parasitic
inductances and capacitances in the switch and wiring, resulting
in a series of damped sinusoidal oscillations
• This effect causes problems in some analogue and logic circuits
that respond fast enough to misinterpret the on-off pulses as a
data stream.
Switches
• Contact bounce
• Solutions
• There are a number of techniques for debouncing (mitigating
the effects of switch bounce). They can be split into :
• Wet contacts
• Timing based techniques
• Hysteresis based techniques.
• Wet Contacts
• Mercury wetted switch contacts do not suffer from bounce
• as once the connection is made the mercury keeps the
contact conducting during mechanical bounce
• Toxic solution
• Timing based techniques
• Range from simple RC circuits to digital sampling
Switches
• Contact bounce
• Solutions
• Timing based techniques
• Simple Series resistor and Cap to ground on the Switch input
• Schmitt Trigger on the input
• Sample the switch state at intervals longer than any possible train
of bounces.
Buttons
• Overview
• Some common Slot Machine Buttons w/switchs
From SuzoHapp’s Web
Page
Buttons
• Overview
• Part of the Button switch
assembly that the end user
activates
• Can be very simple (below)
• Or Complex like those on
a slot machine
• Older style with a lamp
shown on the right
From Suzo-Happ’s Web Page
Buttons
• New Types
• Buttons with LCD displays
• Displays can be changed under game control
• Promoted on many EGM’s that can support Server Based
Gaming
• Example fro Suzo-Happ’s Web site
Buttons
• New Types
• Started as programmable keys for a keyboard
• You can read about the history of LCD Buttons at:
http://www.lcd-keys.com/english/history.htm