Exp_10_fa09

Exp_10_fa09 - Physics 3330 Experiment#10 Fall 2009 Digital...

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Physics 3330 Experiment #10 Fall 2009 Experiment #10 10.1 Fall 2009 Digital Electronics II: Microcontrollers Purpose In this experiment we introduce microcontrollers, powerful single-chip computers that can be programmed to perform almost any digital task. Introduction Let’s suppose you want to build something more complex than the digital circuits we studied in the previous experiment. For example, you might have a Wheatstone bridge and a null detector that you want to hook up to a computer so you can automatically balance the bridge and record the null point, maybe with an adjustable excitation voltage for the bridge. Or, say you want to build a tiny battery powered data transmitter to feed to a dolphin and find out how his body temperature varies while he’s swimming around in the ocean. Since it’s hard to transmit signals through a dolphin, the transmitter should store the temperature data until it is excreted by the dolphin and floats to the surface where your receiver can detect the signal. These and many other applications require complex digital circuitry. Any digital system, including a programmable computer, can be built by combining the gates and flip-flops we discussed in the previous experiment. But it is hardly practical to build something like a computer by connecting together a bunch of TTL chips, since you could easily require thousands or even millions of gates. There are much better ways to get the job done. In fact, if you find yourself using more than a few discrete logic gates in a circuit you are probably making a mistake. As a scientist you should generally try to avoid building anything digital. The first example above could be handled by a PC with data acquisition cards and a power supply with a computer interface. For the potentiometer of the bridge you could use a digital potentiometer or a stepper motor driving an analog pot, both of which can be connected to a computer with commercial hardware. However, for the second example you would probably have to build everything from scratch. There are three general approaches to building complex digital circuits: application specific integrated circuits (ASICs), programmable logic devices (PLDs), and microcontrollers . ASIC is a general term for any complex integrated circuit that is devoted to a very specific task. Examples are chips designed for cell phones, TV sets, or controllers for liquid crystal displays. Generally, ASICs are designed to serve large commercial markets, and so you won’t find anything that will be much help for the two applications mentioned above, or for most scientific applications. But if there is an ASIC that does what you need to do, or that can be adapted to
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Experiment #10 10.2 Fall 2009 your task, you should certainly use it. If you have a really large project with at least a million dollars to spend you could make a custom ASIC that does just what you want. ASIC manufacturers have many ready-to-go design elements (called standard cells),
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Exp_10_fa09 - Physics 3330 Experiment#10 Fall 2009 Digital...

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