Using OP-Amp to Schmitt Trigger

[ericgibbs]

Is the hysteresis set pot just a varaiable resistor to help set it??

hi,
Setting the required level of hysteresis and the upper/lower voltage limits using 'preferred values' of resistors can be tricky.
Problem is, when you change the Rh [fixed] resistor the Vref point moves, so you adjust the Vref and then the switching limits change...

I have found the easiest way is to calculate an approximate value of Rh and Vref,
then include in the Vref and the upper/lower hysteresis circuit, variable resistors.

The variable can be replaced for fixed resistors after you have determined the required fixed values.
[you measure the resistance values of the variable resistors]

Do you follow.?