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Originally Posted by KenWittlief
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The problem with one shot timers is, they are temperature dependant, voltage dependant, and rely on the RC time constant, which also can create a wide range of tolerance issues.
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Guilty as charged, but even so it is silly to argue that they don't have a place in the world.
Point 1: Last week, I needed to exercise a curcuit as I debugged some design issues. I literally built a 555 circuit, had my scope hooked up and was solving the problem in about the same time it would typically take to boot up a PC and open an IDE like MPLab, yet alone designed and debugged a PIC circuit, written code for it, and downloaded and debugged that code.
Point 2: Many applications can live with temperature & voltage dependency as well as wide tolerancing issues.
Point 3: The claim that "real" digital circuits require a clock is a blanket generization that just doesn't hold up to serious evaluation. 1000's of chips, useful ones that even the purest of the pure Digital Gurus could not argue is not a "Digital," have no such clock but depend on internal, well planned logic races to function as designed.
Point 4: The 555 is dirt cheap. The reason that Programming Purists have been able to hold the line on the "GOTO's ARE EVIL" mantra is that (1) you can (almost) always make cleaner, easier to maintain code without them and (2) these work arounds do not cost more. I can tell you right now, the 1000's of engineers that put the 555 in the millions of commercial products that ship each year are not ALL stupid. They are being driven by cost. Professors can argue all they want about inelegant solutions. Jonh Q. Public doesn't pay for elegance, he pays for features. If 555's provide the feature at a lower cost, 555's win the day. If not, they don't.
Point 5: Sometimes Programming, Electronic Engineering and Computer Engineering Purist really get my blood boiling ;-) Perhaps it is just a reflection of the relative youth of these fields, but I can't think of similar analogs in the fields of Civil Engineering, Mechanical Engineering or Industrial Engineering. Have you ever heard a Civil Engineering guru argue that only the only way to cross a valley is with a suspension bridge - all other methods are beneath consideration? Or a Mechanical Engineer ever insist that the only REAL heat engines are based on the Stirling Cycle? I see this kind of borderline religious zealotry all the time in the electronics & computer engineeing worlds and it drives me nuts.
I have already said more than I should have. I will end by just saying that there is no such thing as an ideal solution. All solutions involve tradeoffs. I urge folks to understand advantage and disadvantage not to memorize a set of rules ("don't use gotos," "never use 555s," etc.). In the former you can choose a solution that optimizes your Performance Index. In the latter, you may be able to keep a Prof from giving you an automatic F, but I don't think life is likely to give you an A.
Joe J.