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i use more than one reference resistance R4 and i switch between them using a rotary switch
and its value equal maximum value can the meter measure because Rx= -Vout/Vcc * R4
thanksThat equation is good for the new circuit. Notice that R1 and R2 do nothing but load the op amp down.
The op amp will adjust the output voltage so that the voltage at junction of R3 and R4 is always zero volts, but the output voltage of the op amp cannot go below the power supply voltage of -5V in the real world (even though it might in the simulation world). That means that for Rx greater than R4 the output will not hold to the equation.
thanks Mr Al
* i use R1 , R2 because Vout is negative thus i can't measure it using MCU thus i use R1 , R2 to have a voltage divider V1
then i measure V1 using ADC (MCU) then i calculate Vout while(Vout = 2V1 - Vcc) .
you have an idea about a (max,min) measure range if i replace R4 by a variable resistor
Hi,
A simple improvement would be to add another op amp stage that converts 0 to 2.5v to 0 to 5v.
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