[sdiy] 3 bit A to D with hysteresis?

[Batz Goodfortune]

Y-ellow Paul 'n' all.

At 05:48 PM 5/25/02 +1000, you wrote:
>Can anyone point me to a 3 bit A to D with hysteresis?
>(yeah I now I can do it with a PIC! but, there must be an elegant 
>alternative.. eventually I want to be able to select between 8 inputs by a 
>control voltage, but without problems of 'jumping around' on the edges of 
>the changeovers.)

What about this. This is just an idea. Not properly formulated or anything 
and probably a little high on the parts count but!

Make up a standard sort of 3 bit flash converter (8 opamps/comparitors with 
resistance ladder) but the twist being a window comparitor on each one. 
(Maybe get away with it somewhere further forward in the chain I'm not 
sure.) The thing could only switch when the voltage is in the window. WHen 
it's between windows it can't flip up or down.

I think it's a window comparitor you're needing here. In that you can set 
the hysteresis on both sides of the window. The only way I know of building 
a window comparitor is with a pair of op amps. So that would be 16 op amps 
for your 8 level/3 bit flash. But perhaps with a little experimentation you 
could cancel down using the hysteresis from the level above or something? 
Perhaps using some kind of lock-out. IE: An analogue AND function? IE: can 
only spit a bit if the one below it is out of it's range.

Does this sound plausible? Even in your wildest dreams?

A PIC or an AVR or something would of course be a far cheaper solution. But 
who wants to program one.

Hope this helps.
Be absolutely Icebox.

  _ __        _       ____Happiness is a warm penguin____
| "_ \      | |
| |_)/  __ _| |_ ____       ALL ELECTRIC KITCHEN
|  _ \ / _` | __|___ |  Geek music by geeks for geeks
| |_) | (_| | |_  / /
|_,__/ \__,_|\__|/ /    Bullshit --> http://all-electric.com
                 / ,__   Music -----> http://mp3.com/electrickitchen
Goodfortune    |_____|