Why ADC is giving wrong results ?

[milan.rajik]

Why ADC is giving wrong results ?

I am testing this code in Proteus and also on EasyPIC7. The problem in EasyPIC7 debugging is that when ADC_Read(x) is executed the debugging stucks and doesn't go further. In run mode the code is not working in EasyPIC7. So, I am also testing it in Proteus to see what is happening. I am using 4 MHz clock. ADC result should be 300 for 5V but the adc is varying like 0 to 5x then again 0 to 5x. Both channels are behaving like that. I have not tested other channels. Is it a bug of Proteus or mikroC ADC library ? I am using mikroC PEO PIC 6.4.0 for coding.

Just to simulate the error I am attaching an example adc project. It has to display 300 for 5V adc input on both channels.

Am I missing some register configuration ? ADC result is set for right justified. Comparators are disabled. TRIS is set for 0x03 for AN0 and AN1. ANSEL is set for AN0 and AN1.

Edit: Attachment changed. I had attached wrong attachment earlier.

Tested the project in EasyPIC7 in run mode not debug mode. The adc values vary from 0 to 62 and then again becomes 0 and then goes to 62 and repeats when adc input is varied from 0 to 5V.

- - - Updated - - -

It was a mistake to use unsigned int. The value when multiplied by 300 was exceeding the 65535 value but I changed to unsigned long int and used LongToStr() function but still get incorrect adc value. If I use float then it works fine.



Edit 2:


This works

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Code C - [expand]
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volts = ADC_Read(0);
volts = volts * 300 / 1023;

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but this doesn't work. why? I am using unsigned long int and LongToStr() in mikroC

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Code C - [expand]
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volts = ADC_Read(0) * 300 / 1023;

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[amayilsamy]

Hii ..

In your code

ADCON0 = 0x40; change as ADCON0 = 0x41;

Have enable bit 0 for ADC Conversion..

 

[milan.rajik]

Hi

Thank you for replying. That doesn't cause a problem because ADC_Read(x) function will take care of the ADON and GO/DONE bits in mikroC. Just to configure ADCSx bits I configured ADCON0. My previous post is updated. I have mentioned about the strange behaviour. Please read it.

 

[FvM]

Provided this is your code

unsigned long volts;
volts = ADC_Read(0) * 300 / 1023;

Yes, it will give wrong results according to elementary C type conversion rules.

You'll better write

unsigned long volts;
volts = (unsigned long)ADC_Read(0) * 300 / 1023;