Dave Engvall wrote: > Hi Steve, Jon: > > The Analog Devices chips have really good specs especially at low freq. > How they are rather pricey in todays world of inexpensive chips with > excellent performance. A couple of $14 to $31 chips drives the price of > the finished board up pretty fast. > There is a National tach chip ( LM2917) at much lower prices but also > lower specs. > This is still a unipolar (= unidirectional) F-V converter. > I wonder how well a digital approach with a simple moving average would > work. I'm assuming that a good digital filter would take too much time > to compute but that is someone else's problem. ;-) FPGAs can do digital filters in the MHz range, if you really need it. But, the problem is to filter a discontinuous-time signal (encoder counts) into an approximation of a continuous-time signal (velocity) with minimal delay AND minimal ripple at low speed. NOT trivial.
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