Switches and Pushbuttons Device Peripherals Switches and Pushbuttons

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.

       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 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).

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”

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

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

       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“)

       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 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:

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.

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

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.

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

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

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

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

Dynamic Pushbuttons LCD Technology oLED Technology You can read about the history of LCD Buttons at: http://www.lcd-keys.com/english/history.htm oLED Technology The predominate pushbutton display technology in todays player panels

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 http://www.oledworks.com/technology

Dynamic Pushbuttons Retrieved on August 8, 2013 from http://www.oledworks.com/technology

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. (http://en.wikipedia.org/wiki/Electroluminescence) 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

Dynamic Pushbuttons