1mv resolution 8-bit adc

ragipselcuk · Joined: 21 Apr 2008 Posts: 8

I want to calculate 1mv sensitivity for 8-bit adc.but I cant do it.
please, help me!

counter=0;
do {
delay_us(10);

ADGODONE = 1;
while(ADGODONE);
aDeger =make16(0,ADRESS);
aDegerGecici=aDegerGecici+aDeger;
counter++;
}while(counter < 10);

adeger= (aDegerGecici*125)>>6;

Regards.

Ttelmah · Guest

First, use the compiler functions. Just use 'read_ad' to get the ADC value.
Then, stop and think. 8bit ADC. 256 steps. For '1mV resolution', you could only cover a full scale 'range', of 0.256v. Read the chip's data sheet. Most (all) chips, require the end to end voltage between the ADC Vref values, to be _at least_ 1.8v. Most require 2.5v, and some older chips about 3v.
You will _never_ get '1mV resolution', with the ADC in 8bit mode, over these ranges.

Best Wishes

Matro · Guest

Izzy Prad · Guest

There are ADC chips with 16, 22, 24 or even 32 bit(I think I saw at Newark). That might solve your problem if you really need that accurate.

RLScott · Joined: 10 Jul 2007 Posts: 465

The most straightforward solution is to add an amplifier with a gain of about 20.

Robert Scott
Real-Time Specialties

ragipselcuk · Joined: 21 Apr 2008 Posts: 8

I have got a card. Somebody designed this card and card has got AN0,AN1,AN2 and AN2=AN3=Vref. Used pic16F72. It works 1mV resolution, I can't make that so I asked this question.
I added three pots to AN0,AN1,AN2. When AN1 or AN0 passed the AN3, card proceed the conversion with 1mV resolution.
I didn't understand, I research every theory, but I can't find anything.
If you have got a idea, please tell me.

Thanks everyone.

RLScott · Joined: 10 Jul 2007 Posts: 465

ragipselcuk · Joined: 21 Apr 2008 Posts: 8

The card hasn't got a amplifier, serial resistor only connected with analog inputs...circuit is very simpler...

Thanks...

RLScott · Joined: 10 Jul 2007 Posts: 465