schmitt trigger/op amp based control circuit

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i need to design a control circuit that monitors two voltage levels (14.1V and 13.8) from a solar panel. when the circuit senses the high level voltage (14.1V) it energizes a relay and when the control circuit detect a low voltage input from the solar panel it de-energizes the relay. i want to use a schmitt trigger or an op amp in my control circuit. how do I go about this?
 

You need two comparators, you might be able to use two op-amps instead. It's called a 'window comparator' circuit.

Derive two voltages, 13.8 and 14.1V from a resistor network and feed them to one input of each comparator, connect the voltage you are monitoring to the other input of both comparators. One will now change output state when your input goes beyond 13.8V and the other will change state as it goes beyond 14.1V. Connect these two signals to a flip-flop or other logic circuit so it turns your relay on when one output is present and off when the other is present.

Brian.
 

For such a small window (14.1 - 13.8 = 0.3), I would consider a single comparator with feedback to give hysteresis of 0.3V. No logic needed. Depends on the accuracy needed in the comparisons. Web search "comparator with hysteresis" for many examples and explanations.
 
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