# Voltage attenuator for ADC input

Discussion in 'General Electronics Chat' started by Mr Smiley, May 1, 2010.

1. ### Mr Smiley Thread Starter New Member

May 1, 2010
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Hi,

I'm trying to go through this with different values. I need a base voltage from 10-15 volts in and 0-2.5 volts out to feed an a/d, with a 15v single rail supply. But from the first section of the calculations i'm getting a gain of -0.5, do i just drop the - when calculating a value of 10K for R1 when using R2 as 20k as in your example. Also do i set Vd to 10v ?

Many thanks

Mr Smiley

Last edited by a moderator: May 2, 2010

Feb 17, 2009
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3. ### hgmjr Moderator

Jan 28, 2005
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mr smiley,

hgmjr

Last edited: May 2, 2010
4. ### SgtWookie Expert

Jul 17, 2007
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Oops - hgmjr, can you include a link to the original thread?

A simple voltage divider won't work to take a 15v-10v signal and change it to 2.5v-0v with a single 15v rail.

5. ### hgmjr Moderator

Jan 28, 2005
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Last edited: May 2, 2010
6. ### Mr Smiley Thread Starter New Member

May 1, 2010
6
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Hi everybody,

Hijacking wasn't intended, apologies to all. It was just Ron H's solution was what i needed. That thread was moved to another on my behalf, and now it's been moved again, could you tell me where it is I've looked around and can't seem to find it's new home.

ps, if it's any help, I've found the following web page which gives a op-amp calculator which seems very good for checking chosen resistor and voltages.

http://www.daycounter.com/Calculators/Op-Amp/Op-Amp-Voltage-Calculator.phtml

Mr Smiley

Apr 14, 2005
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657

8. ### Ron H AAC Fanatic!

Apr 14, 2005
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See this thread for a way to do it with a single supply.

EDIT: Oops! I didn't notice that the output slope is inverted relative to the input.
ANOTHER EDIT: Our OP said 10V-15V. SgtWookie said 15V-10V. Which is it?

9. ### Mr Smiley Thread Starter New Member

May 1, 2010
6
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I'm getting confused now

This thread seems to be going round in circles, and moved to new threads; and at every stage confusion is creeping in.

It was original +10 to +15v shifted to 0 to +2.5v and got changed to 15-10v to 2.5-0v .Nobody's at fault, it just seemed to happen.

Ron has solved the problem for me, many thanks Ron, and many thanks to others.

Mr Smiley

Apr 14, 2005
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11. ### aqibi2000 New Member

Mar 2, 2016
1
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Very easy to attain the 15 - 10v to 0 - 2.5V conversion.

This can be achieved by using an inverting op amp and biasing the non inverting terminal by the 15-10V see the attached diagram > http://m.eet.com/media/1050648/C0268-Figure2.gif

Then the next stage is to work on reducing the amplitude of the signal ... apply a Gain 0-2.5V.

Job done...