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1 comparator, 2 threshold voltages from one LDR sensor

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nghonyis

nghonyis

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Hi guys,

I am working on a project and i want to make the one comparator compare 2 different voltages, say for example 1.5V and 2.5V. I have to use only one light sensor for the different voltages. Please help.
 

Not quite sure I understand. Do you mean you want the output high for voltages about 2.5, and low for voltages below 1.5V, i.e., 1 volt of hysteresis?
 

I want a high when a certain voltaghe level is reached, like having the LED on if the sensor measures at 2.5V and LED of if the sensor senses 1.5V
 

Hello!

I want a high when a certain voltaghe level is reached, like having the LED on if the sensor measures at 2.5V and LED of if the sensor senses 1.5V
Click to expand...

Your explanation is not accurate.
Since you gave your explanation after Barry, I think you don't want an hysteresis, so
please can you describe your suystem fully?
What about 2.6V? 2.4V? etc...
What would happen if you input a signal increasing from 0 to 3V?
Same question with a signal from 3V to 0?

Dora.
 

Hi, here is a way to use an op amp as a comparator to drive an led, with hysteresis.



The scope traces show a signal varying between 1.3 and 2.7V.
The led turns on when the signal goes above 2.5V.
It turns off when the signal goes below 1.5V.

The potentiometers allow you to adjust to your desired range of operation.

You can use a comparator if you wish, by adding a component or two to provide positive volts to the led.
 

Use a comparator circuit using OPamp where one input will be the reference and the other will be your input voltage

When the input = reference LED can glow as the op of the op amp provides the supply to the LED when it is not equal the LED is turned off
 

Hello!

Use a comparator circuit using OPamp where one input will be the reference and the other will be your input voltage

When the input = reference LED can glow as the op of the op amp provides the supply to the LED when it is not equal the LED is turned off
Click to expand...

I would be curious to see such a circuit.
A comparator does not output equal / non equal status but lower or higher status.

Dora.
 

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