[sdiy] logic question

[Magnus Danielson]

From: "Paul Maddox" <Paul.Maddox at wavesynth.com>
Subject: Re: [sdiy] logic question
Date: Mon, 16 Apr 2001 20:39:51 +0100

> Alex,
> 
> > i was wondering how one goes about implementing a "if greater than X but
> > less than Y" circuit.  i see a lot of circuits that will do X if greater
> > than a certain voltage, but say i have three LEDs that i'm feeding
> voltage,
> > and these LEDs go on at 1v, 2v, and 3v respectively.  if i get to 2v, i
> > don't want LED1 to still be on, and if i get to 3v, i don't want LEDs 1
> and
> > 2 to still be on.  how do i go about shutting off the first LEDs whent he
> > voltage goes higher?
> 
> If you get one of the LMxxx Display driver chips (cant remember which now)
> they have a BAR mode (which is what you describe as unwanted) and a DOT
> mode which is what you do want.. its just a pin you select either 5v or 0v.

One way may be to mount the LEDs between the outputs of the
comparators. That way will only the led sitting between the opamps for
which the voltage is between light up. The other op-amps will have
both ends at about either of the rails. Just the end diodes is hooked
to the real rails. Easy as pancake!

The National ICs are simpler to use thought.

Cheers,
Magnus