Timers

Overview
A timer is a method for controlling an event sequence as it related to a certain number of events, usually specific periods of time itself. For instance, an egg timer is a mechanical timer that sounds a buzzer over time, an electronic timer controls the change of a clock display, and a software timer can determine how long to wait before executing a particular software command.

Mechanical Timers
Mechanical timers use potential energy such as that of a spring, weight, or chemical reaction with some sort of control mechanism to control the speed of the reaction. For instance, clocks use a gearing system a pendulum and escapement, while egg timers use an internal beater that slows with air resistance.

Electromechanical Timers
Electromechanical timers combine electronic principles with physical mechanics. For instance, some flip-flop switches respond to thermal expansion due to current, causing the switch to change positions. Relays move when an appropriate current is applied provided, and electric motors move over time compared to power applied.

Electronic Timers
Quartz timers use digital logic in order to process time. For instance, the charging and discharging of a capacitor with an inductor and relay forms the most basic electronic timer. Digital logic through components or programmed microprocessing can execute a function after a certain number of cycles. However, most modern electronics utilize the much more accurate quartz timers.

Electronic Crystal Timers
Crystal Oscillators use the resonance frequency of specially designed crystalline pieces (often quartz) to generate a periodic voltage. This can be monitored, and is a very accurate method of timekeeping. As a result, this method is the predominant modern timekeeping method, including clocks and watches where the crystal timekeeping method is far more accurate then the mechanical methods.

Software Timers
Software timers are based off of a series of software events. This can be arbitrary, such as after a number of times a command has been executed, or related to electronic timing signals such as after a certain number of hardware cycles, or by the mandate of an external clock.