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Convert output to 0-5V

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jassi

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hello,

I'm trying to design a barometer, for which i have decided to use MPX4100 sensor. it's output goes as 0.3V-4.9V for 20kPA to 105kPa; the output isn't linear. it's following the equation Vout= Vs*(.01059*P-.152) as can be seen in diagram below (extracted from datasheet). I want to convert this output to 0-5Volts output (using hardware), which is my part of project. I'll be really greatful to you if can please help me out.

Regards
 

One option is to use opamps .. see picture below ..
The first opamp may "shift" the voltage from 0.3-4.9V to 0.0-4.6V and the second opamp may amplify this signal by 1.087 to produce the required 0-5V output ..

Another option is to employ a small microcontroller such as the 8-pin PICAXE-08M, use its PWM output to generate 0-5V and set one of its analog imputs to take 0.3-4.9V (or whatever you need) input signal ..
Take a look at this example:


Regards,
IanP
 

thanks for replying but in your first solution thru opamp wht should be the value of the resistances to convert 0.3-4.9V to 0.0-4.6V and the second opamp signal by 1.087 to produce the required 0-5V output ..

thanks
 

Select the following:
- R1=∞
- R4=R5=R6=R7=10kΩ
and:
- R8=10kΩ
- R9=870Ω
assuming that the voltage between R2 and R3 = 0.3V (I don't know what reference voltage are you going to connect to the top of R2) the output will be 0-5V ..

Supply to the opamp should be +/-8V to +/-15V ..

Regards,
IanP
 

    J

    jassi

    Points: 2
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after i shift the output to 0.0-4.6V, will that make the output linear. let me explain what i'm trying to say, with an example, i know i get 0.3volts for 20kPa (sensor standard value) and now if i get a voltage = 1.575 volts and solve it as pressure = (20/0.3)*1.575=105kPa, but instead the sensor gives 4.9volts for 105kPa now how to handle this problem. if i even shift from 0.3-4.9 to 0.0-4.6V i don't think so i'll come out of this problem.
thanks for previous replies
 

You have to use the formula used by the conversion:

NewVoltage = (OldVoltage - 0.3V) * 1.087
or:

OldVoltage = (NewVoltage/1.087) + 0.3V

and apply it to the pressure formula ..

Regards,
IanP
 

i have to use opamps and produce 0-5 volts i can't use formulas or micro-controllers for this
 

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