[sdiy] comparator feedback resistor

[Keith Daniel]

>most schematics I see with comparators do not have a feedback resistor, but 
>sometimes they do. one I am looking at now uses a TL07X and has a resistor 
>of 2.2M between the + input and the output. now from what I have read it 
>seems that the resistor is there for either hysteresis...

>also, if it's an advantage to include this feedback resistor how do you go 
>about calculating the proper value for it?

It's there for hysteresis, a bit of 'snap'  on the comparator to insure that the integrating capacitor discharges completely. Some prefer a small value capacitor (20 pf).

As for values, I use 1K on the input and 1M from the + to output. No particular reason, it works well enough, and 2.2M would probably work just as well. Breadboard!

Take care.       kwd...