# Calculating a resistor divider circuit to give an output voltage of between 2.5v and 4.5v

#### ericgibbs

Joined Jan 29, 2010
9,864
hi FP,
I have drawn up a simple calculator using LTSpice.
LTSpice is a free download, if you are interested I could talk you thru on how to use this calc.??

E

EDIT:

This is the LTS asc file, load it and give it a run.

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#### Ford Prefect

Joined Jun 14, 2010
173
hi FP,
I have drawn up a simple calculator using LTSpice.
LTSpice is a free download, if you are interested I could talk you thru on how to use this calc.??
E
Thanks ericgibbs - I am VERY grateful.
I tried downloading LTSpice a while ago. Yes, I would love to learn how to use, but I found it had a very steep learning curve and gave up!

#### Ford Prefect

Joined Jun 14, 2010
173
Hi ericgibbs,
I would like to take you up on your offer of learning something about LTSpice.
I will PM you.
Regards.

#### Kjeldgaard

Joined Apr 7, 2016
398
I have some thoughts about the circuits in #18 and #19 posts.

Some years ago we had often this type settings with a potentiometer on the front of a device.

And when it was for production in larger numbers, we used to place a fixed resistor parallel to the potentiometer, which means that the fixed resistor was not more than one tenth of the value of the potentiometer.

The following outline shows how to get a 10% potentiometer to not more than 1% deviation:

I have not spent much time finding standard values, but when R3 is above the nominal, I chose R2 = 1K2 instead of 1K1.

#### Ford Prefect

Joined Jun 14, 2010
173
I have some thoughts about the circuits in #18 and #19 posts.
Some years ago we had often this type settings with a potentiometer on the front of a device.
And when it was for production in larger numbers, we used to place a fixed resistor parallel to the potentiometer, which means that the fixed resistor was not more than one tenth of the value of the potentiometer.
The following outline shows how to get a 10% potentiometer to not more than 1% deviation:
I have not spent much time finding standard values, but when R3 is above the nominal, I chose R2 = 1K2 instead of 1K1
.
Yes, of course!! Thank you Kjeldgaard. This is a very interesting idea.
This will make the voltage output much more sensitive.
Also I am looking and hoping for a range of about 3.5 and 4.0v
So a resistor values at
R1 = 7.5k, R2=1k, P1=1k and R3=3.3k
would give the results and range I was looking for.