Electronic circuit, LED turns on if Vin is greater than or less than a value

[dylandrop]

Homework Statement

Construct a circuit that turns on if it the voltage provided is greater than 3 volts, or less than 2. MUST USE THESE CRITERIA: i<100mA, only one PS. Fewer than ten components.

Homework Equations

None that I know of, but we've covered resistors, caps, inductors, and op amps thus far.

The Attempt at a Solution

I'm pretty lost on this one. We've studied op amps, so I would know how to do this if this involved having one voltage source be greater than another, that is, using a comparator. Where I'm unsure is where you compare Vin to two different voltages. The problem description depicts 2V, 3V, and Vin going into an undefined element (our circuit) and then out to an LED. Unsure if this means that the 2V and 3V are PS's.

Sorry for the vagueness on this one. I'm also kind of unsure, since the problem is poorly worded.

 

[berkeman]

Homework Statement

Construct a circuit that turns on if it the voltage provided is greater than 3 volts, or less than 2. MUST USE THESE CRITERIA: i<100mA, only one PS. Fewer than ten components.

Homework Equations

None that I know of, but we've covered resistors, caps, inductors, and op amps thus far.

The Attempt at a Solution

I'm pretty lost on this one. We've studied op amps, so I would know how to do this if this involved having one voltage source be greater than another, that is, using a comparator. Where I'm unsure is where you compare Vin to two different voltages. The problem description depicts 2V, 3V, and Vin going into an undefined element (our circuit) and then out to an LED. Unsure if this means that the 2V and 3V are PS's.

Sorry for the vagueness on this one. I'm also kind of unsure, since the problem is poorly worded.

My first instinct would be to do it with two comparators. Try sketching up that circuit, and see how many components it takes. Assume that the 2V and 3V inputs are available, so you don't need to make them with resistor dividers off of the power supply. You should include hysteresis around the comparators in a practical circuit, but you may not need that if this problem is dealing with more simple ideal circuits.

Show us what you come up with for a 2-comparator circuit so we can discuss it.

 

[dylandrop]

I'm assuming it'd be something like the attached (sorry for the crappy MS paint job)

 

[berkeman]

I'm assuming it'd be something like the attached (sorry for the crappy MS paint job)

That's a pretty simplified version, and it's missing something on the outputs. Use Google Images to look at various examples of Window Comparators...

 

[DeeNos]

I would suggest starting by breaking down the problem into smaller parts. First, let's focus on the criteria: i<100mA, only one PS, and fewer than ten components. This tells us that we need to design a simple circuit that can handle up to 100mA of current, using only one power supply and less than ten components.

Next, let's think about what the circuit needs to do. It needs to turn on if the voltage provided is greater than 3 volts or less than 2 volts. This suggests that we need to use a comparator to compare the input voltage (Vin) to two reference voltages (2V and 3V).

One possible solution could be to use a simple op amp comparator circuit. This would require only one op amp, a few resistors, and possibly a diode to protect the op amp from reverse voltage. The input voltage (Vin) would be connected to the non-inverting input of the op amp, while the two reference voltages (2V and 3V) would be connected to the inverting input through resistors. The output of the op amp would then be connected to an LED, with a current-limiting resistor to ensure that the current stays below 100mA.

Another solution could be to use a voltage divider circuit with two resistors to create the two reference voltages, and then use a single comparator IC to compare Vin to those voltages. This would require only one IC and a few resistors, making it a very simple circuit.

Overall, the key to solving this problem is to break it down into smaller parts and use your knowledge of electronic components and circuits to come up with a solution that meets all of the given criteria.