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Unformatted text preview: UC Berkeley, EECS Department B. E. Boser EECS 40 Lab LAB4: Audio Synthesizer UID: Lab 4 starts October 18. No new labs in the week of 10/11. Enter the names and SIDs for you and your lab partner into the boxes below. Name 1 SID 1 Name 2 SID 2 The 555 Timer IC Inductors and capacitors add a host of new circuit possibilities that exploit the memory realized by the energy storage that is inherent to these components. In this laboratory we will use capacitors to build timer circuits. Timers have many uses, from lights that turn off automatically after a prescribed period to blinking lights and synthesizers used in sirens or electronic organs. Timers are also used by other electronic circuits, for example as computer clocks. In fact, the 555 timer circuit used in this laboratory is one of the most successful ICs ever (IC stands for integrated circuit, meaning a device that combines several electronic functions in a package): Designed in 1970 by Hans Camenzind at Signetics (later Philips and now NXP) and introduced 1971 (the same year Intel introduced its first—4-Bit!—microprocessor executing up to 60,000 instructions per second), sales are still strong with over 1 billion units sold each year! Can you think of other innovations with similar success and longevity? The first microprocessor has long been relegated to museums. The notorious RC charging and discharging circuit that is at the basis of so many homework and exam prob- lems is also at the center of many timer circuits (exams are practical, after all). For example, the time it takes to charge a capacitor can be used to delay turning on a device. Likewise, discharging sets the time to turn a device off. Combine these two circuits and you have a clock turning on and off at a rate set by a capacitor and resistors. Turing this simple idea into a complete electronic circuit calls for several functions in addition to the capacitor and charging and discharging resistors. Switches are used to alter between charging and discharging cycles. Compara- tors determine when a certain voltage level has been reached. Altogether quite a few components are needed to build that timer circuit. The 555 timer includes all these functions in an 8-pin package. A timer circuit performs two functions: A mechanism for generating the delay, and a device to turn the timer state on and off, based on the delay. The first function is easily realized e.g. by the charging and discharging of a capacitor. The second involved comparing the resulting waveform to set thresholds. Fortunately the circuitry for this function is available as standard components. The most prevalent of these “timer ICs” is the 555. For some reasons ICs typically have numeric “names” with little or no deeper meaning....
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- Fall '07
- timer, VCC, 555 Timer, 555 timer IC