Window Detector Circuit Design: LED Activation for Voltage Thresholds

In summary, the conversation involves the design of a window detector circuit with a diagram provided. The relevant equations for the circuit are mentioned, but there is confusion about the values of the resistors. The issue of output voltage when one comparator wants to drive it high and the other wants to drive it low is also discussed. It is suggested to add hysteresis around the comparators to prevent oscillation.
  • #1
3
0

Homework Statement



I think I know how to do this but wanted to make sure before I actually make the circuit.

Here's a general diagram:
[PLAIN]http://forum.allaboutcircuits.com/image_cache/httphome.cogeco.ca~rpaisley4ComparatorWindow.GIF [Broken]

So as you can see I'm trying to make a window detector circuit that makes an LED turn on if the voltage is below or above a certain threshold. In this case, I want the LED to turn on above 2V or below 1V.


Homework Equations




I think I know how to devise the relevant equations:

VREF1 = R3 / (R1 + R2 + R3) * V+
VREF2 = (R2 + R3) / (R1 + R2 + R3) * V+


The Attempt at a Solution



I'm just unclear on what to make R values. It seems that R2 always comes out as 1/2, which makes sense mathematically (if you set VREF1 = 2, VREF2 = 1) but makes no sense to me in the real world. I've always used resistors with usually at least 100 Ohm values. But maybe I'm wrong. Help?
 
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  • #2
What will be the output voltage when one of the comparators wants to drive it high while the other wants to drive it low? Which one wins? How can you prevent the fight?
 
  • #3
dylandrop said:

Homework Statement



I think I know how to do this but wanted to make sure before I actually make the circuit.

Here's a general diagram:
[PLAIN]http://forum.allaboutcircuits.com/image_cache/httphome.cogeco.ca~rpaisley4ComparatorWindow.GIF [Broken]

So as you can see I'm trying to make a window detector circuit that makes an LED turn on if the voltage is below or above a certain threshold. In this case, I want the LED to turn on above 2V or below 1V.


Homework Equations




I think I know how to devise the relevant equations:

VREF1 = R3 / (R1 + R2 + R3) * V+
VREF2 = (R2 + R3) / (R1 + R2 + R3) * V+


The Attempt at a Solution



I'm just unclear on what to make R values. It seems that R2 always comes out as 1/2, which makes sense mathematically (if you set VREF1 = 2, VREF2 = 1) but makes no sense to me in the real world. I've always used resistors with usually at least 100 Ohm values. But maybe I'm wrong. Help?

gneill said:
What will be the output voltage when one of the comparators wants to drive it high while the other wants to drive it low? Which one wins? How can you prevent the fight?

He's probably using open collector comparators. That would be the traditional way to do it.

@dylandrop -- I'd suggest adding hysteresis around the comparators. Comparator circuits without explicit hysteresis feedback generally oscillate/buzz near the switching points.
 
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1. What is a window detector circuit?

A window detector circuit is an electronic circuit that is used to detect when a signal falls within a specific range or window. It is commonly used in electronic devices to monitor voltage or current levels and trigger an alert or action when the signal falls outside of the predetermined range.

2. How does a window detector circuit work?

A window detector circuit typically consists of two comparators and a voltage reference. The comparators compare the input signal with the upper and lower threshold voltages set by the voltage reference. If the input signal falls within the window, the output of the comparators remain at a low voltage. However, if the signal falls outside of the window, the output of the comparators switch to a high voltage, indicating a detection of an abnormal signal.

3. What are the applications of a window detector circuit?

Window detector circuits are commonly used in electronic devices such as power supplies, battery chargers, and voltage regulators. They can also be used in safety systems to monitor critical parameters and trigger alarms or shut down systems in case of abnormal signals. Additionally, window detector circuits are used in industrial automation for process control and monitoring.

4. How is a window detector circuit different from other types of detectors?

A window detector circuit differs from other types of detectors, such as threshold detectors or peak detectors, in that it monitors a specific range of signal rather than a single threshold or peak value. This allows for more precise detection of abnormal signals and reduces false alarms. Additionally, window detector circuits can be easily adjusted to change the window size, making them versatile for different applications.

5. What are the advantages of using a window detector circuit?

Window detector circuits offer several advantages, including high sensitivity and accuracy in detecting abnormal signals, adjustable window size for different applications, and the ability to monitor multiple signals simultaneously. They also have a simple design and low cost, making them suitable for mass production in electronic devices.

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