Hi,
I am trying to simulate a circuit in LTSpice, in which a potentiometer varies a voltage between -9V and 9V. Using a Schmitt trigger with an LM741 the circuit then detects whether the voltage is within a range of -5V to 5V, if it is then a green led turns on (red off). If it is within the range of -9V to -5V or 5V to 9V then a red led is on (green off). The green led also has a 20-25s delay before turning on using a 555 timer. Please note a Schmitt trigger must be used and other than the potentiometer you only have positive voltages.

Any assistance would be appreciated. Thank you.

 

Please note, I can also use an LM358 which is dual rail

 

*a dual comparator

 

A Schmitt Trigger is the wrong circuit for that purpose. The circuit you want is called a window comparator. It is best to make this circuit with a comparator device rather than an opamp. A suitable device for this purpose would be an LM393 (dual) or LM339 (quad).

Here is a nice ApNote on the circuit

https://www.ti.com/lit/an/sboa221a/sboa221a.pdf?ts=1695652632147

 

Hi,
I am trying to simulate a circuit in LTSpice, in which a potentiometer varies a voltage between -9V and 9V. Using a Schmitt trigger with an LM741 the circuit then detects whether the voltage is within a range of -5V to 5V, if it is then a green led turns on (red off). If it is within the range of -9V to -5V or 5V to 9V then a red led is on (green off). The green led also has a 20-25s delay before turning on using a 555 timer. Please note a Schmitt trigger must be used and other than the potentiometer you only have positive voltages.

Any assistance would be appreciated. Thank you.

Sounds like a homework assignment. Is it?

 

See post #4. You want a window comparator. Avoid using an operational amplifier but rather use a chip designed as a comparator.

Ron

 

Sounds like a homework assignment. Is it?

Using a 741 is a dead giveaway. All the remaining extant parts are at universities, especially the ones with limited funds. Got to use up that existing stock after all.

 

Hi @FluffyMuffin
Sounds like a homework assignment. Is it?

Moderation

 

Is it possible to make a Schmitt trigger with lower and upper trigger points of -5V and +5V? I suppose it could work, but perhaps not with a ‘741 powered with ±9V.

 

you only have positive voltages

How are you supposed to detect negative voltages if you only have positive voltages (which I interpret to be supply voltages)?

 

How are you supposed to detect negative voltages if you only have positive voltages (which I interpret to be supply voltages)?

Couple ways come to mind.

Bias the voltage to be positive with a voltage divider going to the plus voltage

Use a single-supply op amp inverter circuit to invert the voltage.

 

Is it possible to make a Schmitt trigger with lower and upper trigger points of -5V and +5V? I suppose it could work, but perhaps not with a ‘741 powered with ±9V.

But then, even if it could, I don't see how it solves the problem.