How to increase the accuracy ?

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ahmedragia21

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Hi, I'm using a 10k POT to change the position of the servo in degrees , im using an ATmega8 , codes are in C , im using a 5V source for the pot , and 5V for AVCC .
I get for 50mV about a 100 count change in the adc , i wanna get a 0.5Degree resoultion , what to increase ?? increase the resoultion of the ADC ? or the POT value ?
 
.5 degree out of 360 degree (assuming your pot is single turn) = 1/720. so you need a 10bit or higher adc to do it.
 
smanche, its a simple voltage divide , 5V---POT ----> GND

millwood, its a servo motor , it rotates from -90 to 90 ;
so only changing the ADC resoultion not the Pot's value ?
 
The pots value has nothing to do with it, as long as it's low enough in value to correct charge the sample and hold.

Does a servo even give 0.5 degree resolution?, how wide is the dead band on one?, and what is the backlash like?.
 
Your right nigel , but why a 50mV , puts a 100 increase count in the digital value ?
would you tell me the calculations of how the required accuracy affects the resolution of the ADC
 
ahmedragia21 said:
Your right nigel , but why a 50mV , puts a 100 increase count in the digital value ?
would you tell me the calculations of how the required accuracy affects the resolution of the ADC
Click to expand...

It's dead simple - divide 1 by the resolution of the A2D and multiply by 100.

For 10 bits this gives roughly 0.1% resolution, and for only 8 bits it gives 0.4% resolution.

For 180 degrees travel, and 0.5 degree resolution you need 0.3% resolution, so 8 bit isn't good enough - but 10 bit should be fine.
 
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