Author Topic: Settable Hysteresis in this example  (Read 656 times)

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Offline alank2

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Settable Hysteresis in this example
« on: October 05, 2015, 02:58:40 am »
I've been playing around with a MAX997 as an input stage to a frequency counter.  I used a pot to set a trigger point and fed that to the - input and fed the signal t the + input.  This works pretty well, but I wondered - can you use a dual version MAX962 to be able to set both an upper trigger and a lower trigger?  What type of circuit could accomplish that?  If you just doubled the single example and had a pot for each comparator and fed the input signal to both + inputs, then the outputs might be:

HH
LH
HL
LL

HH you would want to be high, LL you would want to be low, but you would want LH or HL to remain unchanged.  What type of circuit would accomplish that taking the two comparator outputs and turning them into a single one?
 

Offline T3sl4co1l

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Re: Settable Hysteresis in this example
« Reply #1 on: October 05, 2015, 03:33:00 am »
Take a look at the internal diagram of a 555.  It's a window comparator, but instead of wired-OR outputs, an RS f/f is used to provide hysteresis.

If you like threshold +/- (hysteresis band)/2 better, that can be done with a traditional bistable multivibrator (which might be what you have already?) where the +FB resistor is adjustable.

Tim
Seven Transistor Labs, LLC
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