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Need help in designing simple opamp circuit.

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dani

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Dear all,

I have a photoelectric sensor whoe's out put varies with the intensity of light from 100 mAmps to 800 mAmps. I want to read this input from PIC Microcontroller. Simply it is possible but the scale is very narrow so i want to design a low noise opAmp circuit which can amplify the sensor output 10 times or at least 5 times. Please guyz help me in this regards..


Thanks
Dani
 

Look up designs for "transimpedance" amp. Basically you hook up the current source to the input, and it spits out a voltage. You can easily set the gain as high as you need for your circuit, and the noise contribution should be negligible unless you have a fancy sensor.
 

why don`t you use a simple voltage divider, when the current changes the voltage drop across the resistor also changes. Read the voltage by MCU.
 

oh hoo.. realy a mistake..

I have misstyped in hury .. it is not 100mAmps to 700 mAmps , but the millivolts. I think it is bit simple circuit to make with opamp but as i am less on electronic side and more on programming side.. so guyz i need help..


regards///
 

You can also do it without an opamp. Like you said the photoelectric sensor output from 100mV to 800mV. Directly read the voltage across the shunt resistor by the ADC.
 

Yes i can.. but i want to amplify the output. Because it is too low. So i want to design it with opamp which can amplyfy the sensor output at least 5 times. Also the system supply is +5V and 0V.

Regards.
 

The schematic below will give you about 5.7 Gain & and will amplify your input. But this amplifier is a very basic design.
 

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