# subtract from and divide a 0-5v signal

#### elRey

Joined Feb 23, 2009
65
I had a 0-5v input that I need to subtract and divide.

Either subtract 1.88v then divide be 3
or divide by 3 then subtract 0.63v.

Output only needs to be positive so any negative can be 0v.

Output should be a 0-1v signal extrapolated from the 1.88v - 4.9v range of the 0-5v signal.

What the easiest way to achieve this?

Rey

#### steveb

Joined Jul 3, 2008
2,436
What the easiest way to achieve this?
I'm doubt this is the easiest way, but it is probably the most straightforward way. Using two stages with inverting configurations gives predictable performance, as well as flexibility if you need to change something.

If I made a math mistake, or if you want to tweak something, you should have no trouble working it out.

I recommend dual power supplies with plenty of head-room, since it is the easiest way, but you may be able to adapt this to a 0-5VDC power supply if you are careful and use good single supply opamps.

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#### elRey

Joined Feb 23, 2009
65
What is the output if input is below 1.88v? the input is the full 0-5v I just need to register the 1.88-4.9v range with anything below outputting 0v.

Your math looks good to me (not saying much).

Again, thank you.

#### steveb

Joined Jul 3, 2008
2,436
What is the output if input is below 1.88v? the input is the full 0-5v I just need to register the 1.88-4.9v range with anything below outputting 0v.

Your math looks good to me (not saying much).

Again, thank you.
If you need to limit at ground, you can use a single supply op amp and use ground for the negative supply. Or, (preferably) you can implement a precision clipper/limiter. There are various methods for clipping with an opamp and you may be able to integrate one directly into the 2'nd stage of your circuit.

I've attached a picture of one circuit which I pulled out of the following book:

IC Op-Amp Cookbook by Walter G. Jung

http://www.amazon.com/Op-Amp-Cookbo...=sr_1_1?ie=UTF8&s=books&qid=1252119997&sr=8-1

In my opinion, this is a book worth having.

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