Exp_9_fa09 - Physics 3330 Experiment#9 Fall 2009 Digital...

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Physics 3330 Experiment #9 Fall 2009 Digital Electronics I: Logic, Flip-Flops, and Clocks Purpose This experiment introduces some of the fundamental circuit elements of digital electronics. These include three kinds of logic gate , two kinds of flip-flop (single bit memory), and the 555 timer chip used as a digital clock. Introduction In almost all experiments, the signals that represent physical quantities start out as analog waveforms. To display and analyze the information contained in these signals, they must be converted to digital data. Often this is done inside a commercial instrument such as an oscilloscope or a lock-in amplifier, which is connected to a computer through a digital interface. In other cases data acquisition cards are added to a computer chassis and the analog signals can be connected directly to the computer. Scientists usually buy their data acquisition equipment rather than build it, so they often don’t have to know too much about the digital circuitry that makes it work. Almost all data is analyzed with a computer, but like other users scientists don’t often have to know much about the digital circuitry inside their computers. We emphasize analog electronics in the course because scientists usually have to know much more about it to design and build their experiments. On the other hand, there are plenty of reasons to know something about digital methods. The author of our text (physicist Paul Horowitz) has built custom digital signal processors to search for signs of extraterrestrial intelligence in radio telescope signals, and particle physicists have built customized computer hardware to make calculations in quantum chromodynamics (the theory of the strong force). If you try to repair a commercial instrument like a modern lock-in you will find that it is full of digital electronics. The trend in modern instrument design is to do as much digitally as possible; even the front-panel knobs are not really analog controls, rather they are coded switches or optical encoders that generate digital data directly. An increasing number of analog parts can be controlled digitally, for example you can buy digital potentiometers that behave exactly like an analog pot, but look more like an op-amp chip, and instead of controlling the position of the wiper with a knob, you send a digital code into some of the extra pins. In digital circuits the voltage on a wire takes one of only two values called logic HIGH and logic LOW, corresponding to a binary 1 or 0. Information is conveyed by the pattern of HIGH and LOW voltages. A single wire can convey just one bit of information at any one time. When the information to be conveyed requires more than a single bit, either more wires can be used to Experiment #9 9.1 Fall 2009
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convey data (parallel digital data), or a sequence of bits can be sent over time as HIGH’s and LOW’s moving along a single wire (serial digital data).
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This note was uploaded on 11/10/2009 for the course PHYS 33 at Colorado.

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Exp_9_fa09 - Physics 3330 Experiment#9 Fall 2009 Digital...

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