# EEVblog Electronics Community Forum

## Electronics => Beginners => Topic started by: wolfrum on March 23, 2012, 12:46:13 pm

Title: Scaling of sensor voltage to desired linear output
Post by: wolfrum on March 23, 2012, 12:46:13 pm
I am working on a "opamp" based project where the sensor values vary from  0.7V to 1.9V and this needs to be scaled to trigger another circuit(PWM generator) which operates from 4.7V to 5.3V.
Can anyone suggest a nonlinear amplifier for the above. My project involves PID control so I cannot go for discrete amplification using programmable gain amplifier.
Title: Re: Scaling of sensor voltage to desired linear output
Post by: sacherjj on March 23, 2012, 01:35:56 pm
I am working on a "opamp" based project where the sensor values vary from  0.7V to 1.9V and this needs to be scaled to trigger another circuit(PWM generator) which operates from 4.7V to 5.3V.
Can anyone suggest a nonlinear amplifier for the above. My project involves PID control so I cannot go for discrete amplification using programmable gain amplifier.

I don't think you want a non-linear amplifier.  I think you want and amplifier with a gain of (1.9-0.7)/(5.3-4.7) = 1.2/0.6 = 0.5.  You also want a DC offset of 5 - (1.9+0.7)/2 = 5 - 1.3 = 3.7 V

So an opamp circuit with gain of 0.5 is pretty simple to calculate.  Then you add another chain with a voltage reference.  Or some of the better circuit monkeys might be able to show how to do this in one chain.
Title: Re: Scaling of sensor voltage to desired linear output
Post by: Bored@Work on March 23, 2012, 01:36:35 pm
Why non-linear? Unless you didn't tell us everything, what you want to do is all very linear. This sounds like a job for an opamp, configured as an adder, adding 8.7V to the signal on input, and with a gain of 0.5. Or first a division by two, and then adding 4.35V.
Title: Re: Scaling of sensor voltage to desired linear output
Post by: wolfrum on March 23, 2012, 01:56:57 pm
Thank you very much got it