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#### I have a signal that is 5mA rms. I need to convert this to 5V with a DC bias which has to be given to the arduino ADC. I need your help in designing a simple opamp circuit that can do the following

convert the 5mA RMS signal to 5V peak to peak with a DC offset such of 5V.
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### Author Topic: opamp current to voltage converter  (Read 877 times)

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#### shiva kumar

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##### opamp current to voltage converter
« on: February 17, 2017, 08:29:18 am »
I have a signal that is 5mA rms. I need to convert this to 5V with a DC bias which has to be given to the arduino ADC. I need your help in designing a simple opamp circuit that can do the following

convert the 5mA RMS signal to 5V peak to peak with a DC offset such of 5V.

#### Zero999

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##### Re: opamp current to voltage converter
« Reply #1 on: February 17, 2017, 09:57:14 am »
Quote
convert the 5mA RMS signal to 5V peak to peak with a DC offset such of 5V.
I wouldn't recommend that. It would give you a 0 to 10V volt output, which is too high for the ADC. You need 5V peak to peak with an offset of 2.5V.

I have a signal that is 5mA rms. I need to convert this to 5V with a DC bias which has to be given to the arduino ADC. I need your help in designing a simple opamp circuit that can do the following
Where is the 5mA signal coming from?

Is it purely AC? I.e. no DC bias on the current signal?

If so and the input impedance doesn't need to be really low, this could be done passively with a couple of resistors, forming a potential divider, and a capacitor.

5mARMS = 5*2*20.5 = 14.14mAP-P

We want to scale that to 5V peak to peak, which can be done with a resistor:
R = V/I = 5/0.01414 = 353.55

If we use a potential divider and a 5V supply to bias it around 2.5V, then the resistor values need to be doubled, as the input impedance is equal to both resistors in parallel. R = 353.55 * 2 = 707R1

« Last Edit: February 17, 2017, 01:32:28 pm by Hero999 »

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##### Re: opamp current to voltage converter
« Reply #2 on: February 17, 2017, 01:29:24 pm »
Here is a tool you can use to calc vales to generate offset and handle the AC input signal.

http://masteringelectronicsdesign.com/differential-amplifier-output-common-mode-voltage-calculator/

Regards, Dana.
Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer

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