On the homework, you're supposed to design me a pulse height discriminator, a circuit that detects when its input has gone above a certain threshold level. The simplest way one can do it is probably this, a single diode and capacitor. This circuit isn't great, though, since for one the threshold voltage is basically limited to the diode's forward voltage drop. That particular problem can be cured, but generally speaking, it is just not very flexible.
A much more elegant solution, like we talked about in class today, is to use a comparator. They're cheap, simple, and plentiful. This way you can make zero-crossing detectors (when does a signal change sign?) or peak detectors. The LM311 datasheet has some nice examples - look at the zero-crossing detector, and positive/negative peak detectors [pulse-height discriminator]. These circuits do basically what we want. [The LM110 in those circuits is just a 'follower' like we talked about today. All it does is makes its output the same as its input, so for the purposes of understanding the circuits, ignore it.]
So, why is this a homework problem? The rpm readout circuit you'll begin building next week will rely critically on this sort of circuit, so by the time you have to build it, you'll already have a working design ready. Details on that project to follow this weekend, we'll begin on Monday.
A much more elegant solution, like we talked about in class today, is to use a comparator. They're cheap, simple, and plentiful. This way you can make zero-crossing detectors (when does a signal change sign?) or peak detectors. The LM311 datasheet has some nice examples - look at the zero-crossing detector, and positive/negative peak detectors [pulse-height discriminator]. These circuits do basically what we want. [The LM110 in those circuits is just a 'follower' like we talked about today. All it does is makes its output the same as its input, so for the purposes of understanding the circuits, ignore it.]
So, why is this a homework problem? The rpm readout circuit you'll begin building next week will rely critically on this sort of circuit, so by the time you have to build it, you'll already have a working design ready. Details on that project to follow this weekend, we'll begin on Monday.
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