SAR ADC with pic

[jeanninemtv]

how to make a SAR ADC for a 16f84a??  i read that you can acchieve 10 or 12 bit accurate... its true?

[8K51]

Hi

If you code SAR (successive approximation register) algorithm in 16f84 and drive a 10/12 bit DAC outside with ref and comparator you can make a SAR ADC with 10 or 12 bits resolution. This is not 10 or 12 bits accuracy !!
Noise considerations, DAC accuracy and ref won't allow, IMHO, such accuracy.

regards

[Tre]

It is probably true that you can make a 10-12 bit SAR ADC, but you wouldn't be able to get much frequency since SAR's oversample significantly and noise shape.  I'm not entirely sure how you implement the noise shaping either.  At any rate, a link would be interesting.

[8K51]

Hello Tre !

...."oversampling and noise shaping" ... maybe you mean Delta-Sigma converter ?

[jeanninemtv]

lol

no clear ideas about the algorithm!!!

i am so confused

[8K51]

Ok , I try to explain more (8bits)

hardware :
-16F84 sends a byte to a DAC (or R/2R ladder)
-Dac's voltage ouput goes to - pin of a comparator
-voltage to convert goes to + pin of same comparator
-comparator's ouput return in some 16f84 input

software:
1. pic sends 1000 0000 ....
    ...get comparator's ouput in bit 7 of a variable.
   ==> LSB (Bit7) is known
2  according to comparator's output :
    pic sends 1100 0000
                or 0100 0000
                get comparator's ouput in bit 6 of same variable
                ==>  Bit 6 is known...

3 The next try gives bit 5... and so on

This method sens 1/2 full scale first, then 1/4 or 3/4 according to previous result......

regards