1. Switches and Pushbuttons
Device Peripherals
Switches and Pushbuttons

2. Switches Overview Used in many devices Some common types below
      
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.

3.       
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[

4. Switches Contacts Actuator
      
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).

5. Switches Contact arrangements Switches classified according
      
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”

6. Switches Switches Normally Opened/Closed Changeover switch
      
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

7. Switches Changeover switch
      
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

8.       
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 mis- match 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“)

9.       
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

10. Switches Types SPDT DPST DPDT Single pole, double throw
      
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:

11. Switches Contact bounce Also called chatter
      
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.

12. Switches Contact bounce Solutions
      
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
Range from simple RC circuits to digital sampling

13. Switches Contact bounce Solutions Timing based techniques
      
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.

14. From Suzo-Happ’s Web Page
      
Static Pushbuttons
Overview
Some common Slot Machine Buttons w/switchs
From Suzo-Happ’s Web Page

15. From Suzo-Happ’s Web Page
      
Static Pushbuttons
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

16. Dynamic Pushbuttons New Types of Dynamic Pushbuttons
      
Dynamic Pushbuttons
New Types of Dynamic Pushbuttons
Started as programmable keys for a keyboard
LCD and oLED pushbuttons are found in newer player panels
Fig. 1 Programmable OLED Button Panel

17. Dynamic Pushbuttons Programmable Pushbuttons
      
Dynamic Pushbuttons
Programmable Pushbuttons
Displays can be changed under game control
Greater flexibility in multigame machines
Different games and max bet configurations are set in machine options.
The dynamic pushbutton displays the button function for the selected game configuration

18. Dynamic Pushbuttons LCD Technology oLED Technology
You can read about the history of LCD Buttons at:
oLED Technology
The predominate pushbutton display technology in todays player panels

19. Dynamic Pushbuttons oLED Technology
OLED, like LED, is a solid state lighting (SSL) technology.
OLED lighting is composed of thin organic layers sandwiched between two electrodes.
When DC current is applied, charge carriers from the anode and cathode are injected into the organic layers, electroluminescence occurs and visible light is emitted.
Retrieved on August 8, 2013 from

20. Dynamic Pushbuttons
Retrieved on August 8, 2013 from

21. Dynamic Pushbuttons oLED Technology Electroluminescence:
Is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field. (
Advantages:
Lighter: OLED substrates can be plastic rather than the glass used for LEDs and LCDs
Consume less power and dissipate less heat: OLEDs do not require backlighting like LCDs

22. Dynamic Pushbuttons