OK, just had to confirm - it wouldn't have been working otherwise.Question #1. Yes. The Vref is the - input.
Yeah, you have to be careful with the hysteresis. If you try to use too small of a hysteresis resistor with a comparator, things get goofy really quick. Better to start out with high values, and then if it proves to be not enough, look first at the input to see if maybe you could remove some noise.Question #2 Yes. 10 meg. That's my best guess of a positive feedback value for between 4-5 mV of hysteresis.
Absolutely! Good call by AudioGuru. As it is, the current is pretty low for that Zener you're using.Question #3 Right now the Zener's a 1 watt 1N4733 from the Shack but I got some BZX79C5V6's on the way from Mouser that AudioGuru recommended. They're a 1/2 watt and run on 5 mA compared to the 40 mA I'm putting thru the 4733. No reason to drain the batteries anymore than necessary ...
Don't worry about the down side - that's when the motor will be taking a nap anyway!Being the kind of person who can't leave new toys alone I've been running the motor some more. Hard to tell with a DMM but it seems to respond very briskly on the up side. When I throttle down things get a little goofy and slow. Up and down even but again, with a DMM I can't really say.
Well, actually - your idea was to short the base of the TIP120 to ground, which WOULD work - however, you would be wasting power across the 1k base resistor for the entire time the motor was running. Not a happy thought with the gas prices of today!Been thinking about "preserving the signal." That's probably a small current on the output of the speed sensor circuit? Am I possibly trying to do too much with it? Could be! Most of my projects attempt to defy the laws of physics some where along the way!
Let's just try to "lock in" what exists at the moment; a snapshot if you will. That way, if things go awry, we can return to this point later. It's a reality check.
Have a look at the attached - the top half is (basically) what you have already, without your proposed modification. The bottom half is what we've been fiddling with the last day or so.
Note that the comparator inputs have the - on top and the + on the bottom. Sorry, I can't change that. It's very counter-intuitive, and may be hard to get used to (it still trips me up)
Anyway, look at it and if you see any glaring errors thus far, let me know.
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