voltmeter with adc0831

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kiranswaps

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dear freinds
i want to design a voltmeter of range 0 to 0.1 volts using 8 bit adc (ADC0831) and atmel microcontroller 8051 witha full scale resolution .

00000000b should represent 0volts
11111111b should represent 0.1volts

please help me how to go about this
thanks
 

Use an opamp to amplify the signal to give 0-5V (gain of 50), or whatever the reference voltage you use for the A2D is.

In this days though it's a clumsy solution using an external A2D, there are many microcontrollers with inbuilt A2D you can use - often cheaper than buying an external A2D.
 
Well using the Op amp amplifier is an option. From the ADC0831 datasheet, you can also adjust the span using Vref. Setting Vref to 0.1v makes an analog input of 0.1v correspond to 11111111 output. Vref of 0.1v may be obtained from a voltage divider chain of resistors.
 

What does the datasheet says about the accuracy of the A2D when using such a low reference?, generally low reference values lose considerable accuracy.
 
Thanks for the suggestions. Actually i tried the same thing from a book by "jan axelson", below is the diagram of the same thing. But it didn't worked. actually i'm new to op-amps. please explain me in detail. one thing more one of my friend told me a op-amp wouldn't give full linear response? is it true? please help me out, & which op-amp should i use.
 

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First thing that's important to know, that not all OP-AMPs are Rail-to-Rail. That means that their output can't reach GND and (or) VDD level. For example old 1458 or 741 can't do so. This would intact linearity of A2D @ sensing voltages near GND or VDD. Try using LM358 (dual OP-AMP) or LM324 (quad OP-AMP), their output ca swing to GND and to VDD-1.5V.
 
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