Fixed threshold difference Schmitt trigger?

[SittingBear]

I want to change the high threshold level by a potentiometer, or similar component, manually while always keeping the difference of levels between the thresholds equal.

Example:

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High: 2v Low: 1.8v
Then change potentiometer to raise high-threshold:

Code: [Select]

High: 5v Low: 4.8v
or a ratio (90% low to high ratio as above):

Code: [Select]

High: 5v Low: 4.5v
I've tried with messing around with the Vref value, but I'm not sure if that's the proper thing to do.

Is this even possible, and if so how? Thanks very much in-advance for any help!


Below is the circuit I have drawn up so far (it's a scan so forgive the angle).

[T3sl4co1l]

That's the basic idea.  You don't really need the follower from the pot, if you dimension the pot to be a low resistance relative to the feedback divider.  Or if you want the dead band proportional to setting, use a current source to put some voltage across the pot and the pot resistance adds in series with the feedback resistor.  (The pot alone, with voltage sources and/or resistors at either end, won't give a linear response; the Thevenin equivalent is lowest towards the ends and highest in the middle.)

Tim