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Timers

Timers. Timers. Mati Chessin 10/07/04. Intro to Timers General Uses 555 Timer. Contents. Timers. What is a timer? A timer is a device that oscillates at an exact, programmable frequency

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Timers

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  1. Timers Timers Mati Chessin 10/07/04

  2. Intro to Timers General Uses 555 Timer Contents Timers

  3. What is a timer? A timer is a device that oscillates at an exact, programmable frequency In an electronic device, the timer will be used to coordinate actions and keep components working at the same rate Introduction Timers

  4. 1880 - Piezoelectric effect discovered by Jacques and Pierre Curie 1905 - First hydrothermal growth of quartz in a laboratory by G. Spezia 1918 - First use of piezoelectric crystal in an oscillator 1927 - First quartz crystal clock built 1934 - First practical temp. compensated cut, the AT-cut, developed 1956 - First commercially grown cultured quartz available 1971 - Introduction of 555 timer by Signetics (later acquired by Philips) Introduction Timers

  5. How do timers work? Timers are regulated by an oscillating device, usually a crystal The crystal is made of a piezoelectric material, such as quartz As crystal vibrates, it produces voltage when compressed and the opposite voltage when expanded By vibrating the crystal at its natural frequency, a circuit can be created to produce a very regular timing signal Higher oscillation frequencies yield lower output voltages A purely electronic timer can be made by utilizing a capacitor and resistor to regularly store and discharge voltage Introduction Timers

  6. Timers are used in many electronic devices: Examples: Clocks, radar, computers, microwaves, robots, HC11, etc… Used to measure the time between inputs (leading or falling edge of signal) Used for pulse width measurement Used to create a time delay General Uses Timers

  7. A Single device can have multiple timers. These could be both built-in or external. For example: General Uses Timers HC11 could regulate a 555 timer that controls an LED HC11 – Uses crystal for timing

  8. Common Applications: Monostable Multivibrator Holds a state (“high” or “low”) until triggered Once triggered, keeps other state for a determined amount of time General Uses Timers Input signal High Low Dt

  9. Common Applications: Bistable Multivibrator Can hold either the high or low state When triggered, it switches state General Uses Timers Input signal Low

  10. Common Applications: Astable Multivibrator Automatically switches between high and low states Becomes a rectangular wave generator General Uses Timers High Low Dtlow Dthigh High Low Dtlow Dthigh

  11. Most common timer Costs about $0.50 A single pulse lasts 1.1 ms 15,400 seconds is the longest time it can be set to The 555 Timer Timers

  12. + pin 2 0 3/2 Vcc pin 7 0 + control F/F 0 +Vcc pin 3 0 + RESET 0 The 555 Timer Timers Astable 555

  13. The 555 Timer Timers

  14. http://www.me.gatech.edu/mechatronics_lab/LabMaterials/EExercise2.pdfhttp://www.me.gatech.edu/mechatronics_lab/LabMaterials/EExercise2.pdf http://www.me.gatech.edu/charles.ume/me6405Fall01/ClassNotes/Timer_fall_01.ppt http://www.madsci.org/posts/archives/may98/895289339.Eg.r.html References Timers

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