hi,

im working with PIC mcu, i go through different tutorials and examples regarding ADC module.

My mcu has 10 bit resolution for conversion. it means, ADC divides input volts by 1024. but i do not understand why do we divide ADC results again with 1024. for example

tmp = ADC_Read(0);
tmp = tmp/1024; // why result is divided by 1024 as ADC has already done it
tmp = tmp*5; //convert back to 5 volts

my second question is, can i calculate expected ADC result, for example if volts on LDR pin are 3.7, how can i calculate expected results of ADC 3.7/1024 ?? right?

thanking you.

 

The ADC has 10 bits that will give you 2^10 possible conversion results in the range from 0 to 1023. The results are always converted against a reference voltage. In your case it will probably be the VCC voltage of your MCY. Each bit in the conversion result will have a bit weight equal to (Vreference/(2^10))
So let us assume that your Vreference is 5 volt. Your bit weight will be (5/(2^10)). If your ADC conversion result is 509. You multiply 509 with the bit weight. To convert the reading back to volt

 

thanks, im little clear about it, but please explain, why do we divide adc results with 1024 in code also, i thought result is already divided by 1024 by ADC??

tmp = ADC_Read(0);
tmp = tmp / 1024;

 

thanks, im little clear about it, but please explain, why do we divide adc results with 1024 in code also, i thought result is already divided by 1024 by ADC??

tmp = ADC_Read(0);
tmp = tmp / 1024;

You multiply the conversion result with the bit weight that is constant. 2^10=1024. Then the bit weight will be Vref/1024. It is better that you find out of this by your self. Here is a good free Ebook. The first part of the book will sort things out for you I guess http://www.analog.com/library/analogDialogue/archives/39-06/data_conversion_handbook.html