Hi all,
i've been looking for a circuit may be based on OP AMP solution.
My requirement is that i am feeding varying input voltage (0 to 24V) to an circuit (could be op amp) it's output would be 0 to 3.3V.
So thing is my output should be correlated with input that means
1. Say input is 0% (0V) my output shout be 0% (0V).
2. Say input is 50% (12V) output should be 50% (1.65V)
3. Say input is 100% (24V) output should be 100% (3.3V)

Do anyone have idea on how to have circuit for this.
Thanks,
-Santhakumar.

 

All you need is a two resistor voltage divider if the 3.3V load is a high impedance.
For such a load you could use a 1.62kΩ resistor to ground connected to a 10.2kΩ resistor going to the 0-24V source. The junction of the two resistors gives you 0-3.3V (nominally 0-3.29V).

What is the load?

 

Two resistors in a voltage divider across the 24v supply, 16K, 100K, will give you 1.65v @12v, 3.31v at 24v.

 

Two resistors in a voltage divider across the 24v supply, 16K, 100K, will give you 1.65v @12v, 3.31v at 24v.

Did you read my post?
My resistor ratios give an output slightly closer to the desired.

 

My resistor ratios give an output slightly closer to the desired.

My resistor is better than your resistor-? Really?!?!? Are you running for president?

ak

 

Those old resistors are losers.
We'll build a better resistor. You'll love it. It will be great!

 

1% resistors almost always arrive at a more accurate solution, but I have a 100K and a 16K in my parts bin. It's a matter of convenience vs accuracy. Pick one.

 

My resistor is better than your resistor? Really?!?!?

 

View attachment 102082

You can tell from the size of the capacitors.

 

My resistor is better than your resistor-? Really?!?!? Are you running for president?

Hell no. How did politics get into this?

But for those interested nit pickers (and I assume you're not one), for an arbitrary resistor attenuation using 1% resistors there are generally many combinations of resistor values that give close to the desired value but some are closer than others. To determine the optimum combination I wrote a short visual basic program a number of years ago that looks at the combinations and lists them according to how close they are to the desired.
Here is a screen shot of the values to get the desired attenuation of 3.3/24 = .1375
The optimum is 1.62k and 10.2k.
Of course that delta doesn't include the effect of the 1% resistor tolerance.

 

How about: 24V to 18K+2.7K with 3.3K to gnd. The output (0 to 3.3000V) across the 3,3K can be buffered with a X1 op-amp if needed.

 

Hi All,

Thanks for the Answers and i can use it in my circuit.
Is there any other ways we can make it without resistor divider. May be by using OPAMP comparator.

 

Is there any other ways we can make it without resistor divider. May be by using OPAMP comparator.

No. A comparator is not a voltage divider.
Why do you want to avoid the cheapest, simplest, most accurate way to do this?
I think I can do this with an op-amp, but why add the extra parts?

 

Hi #12,

Any way i'm gonna use opamp in my circuit so that i just want to hear more suggestion on this to have other options.

-SK

 

Ok go ahead and use an op amp.

Resistance is useless!

 

Ok go ahead and use an op amp, like this circuit

My circuit has more useless parts than your circuit.
and it requires a dual voltage power supply.

 

@#12,, me thinks he wants to make it more useless, may need a Bigger op amp like a TDA2040

 

@#12,, me thinks he wants to make it more useless, may need a Bigger op amp like a TDA2040

I think he's learning about op-amps and just has to see one in action.

 

Hi #12,

Thanks for your circuit, really appreciate your opamp circuit.
I would use resistor divider rather using dual opamp and dual supply.

And this output of divider would goes to ADC.. I would like read consistent values from the divider and so ADC.
care can be taken at software level. but hardware level how effective i can accomplish it..

thanks.

 

The consistent values start with your power supply. I don't know whether the ADC tracks the power supply voltage or not. I don't know whether to instruct you on generating a stable voltage reference or expect the ADC to adapt if it is connected to the same 5V line as the resistors. You just stepped outside my limitations.