gene heskett wrote: > > Jon, while the encoder I built for the lathe spindle was pretty crude, one > of the things I did in my research was to make it an given that the opto > device chosen had an active, high speed CMOS rail to rail output. While > the qradrature may not have been accurate enough to be usable as a velocity > detector, the output of all 3 channels is absolutely noise free. I may yet > carve me another wheel, from even thinner material which would allow me to > use a pcb sized drill for the mill to cut it with. > > I think, when any of us is shopping for an encoder, any encoder with a TTL > level only, or open collector type output should be removed from our > purchase consideration. Even differential outputs, which need twice the > wires, should not be immune to this purchasing rule. > > They are simply too susceptible to stray noise pickup to even be considered > when they are in a high impedance state 50% of the time. > > I certainly never advocated buying an open-collector encoder. I have used a few, and they work, but I feel a lot more comfortable with "totem-pole" drivers that are always driving the signal at a low impedance. I don't think there is anything wrong with "TTL" drivers as opposed to CMOS. Well, anything made after 2000 is goign to be CMOS for sure.
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