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 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 • 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 Suzo-Happ’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