# Linear Equation using opamp; 0.4 to 3.6 V FSR to 0-3.3V scalling circuit

Discussion in 'General Electronics Chat' started by Manjunath CV, Sep 25, 2008.

1. ### Manjunath CV Thread Starter New Member

Sep 25, 2008
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want to convert an output of one of the module whose full Scale Range is 0.4 to 3.6V ... this needs to be scalled to FSR 0 to 3.3V ... when corellated this gives a linear equation Vout = 1.03125 * Vin - 0.4125, i can use the VCC to be between 4 to 5V, how can this be implemented using Opamps. with an error budget of 20mV max
Rgds,
Manju

Dec 27, 2007
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3. ### mik3 Senior Member

Feb 4, 2008
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If you want to minimize the offset errors then you have to use precision op-amps. They are designed to have low offset voltages. Also, for better results use resistors with an accuracy of 1% or less.

4. ### scubasteve_911 Senior Member

Dec 27, 2007
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Using 1% isn't even going to help him.. His total 'error budget' is 20mV. Due to gain error alone, assuming about a gain of 1, he can be off my 2% not assuming anything else. (2 resistors, each going away from eachother), 2% of about 3V is 60mV.

He needs 0.1-0.2% resistors with good tempco if he wants accuracy over range. This is just one factor for a circuit like this.

Steve