Arduino UNO and Arduino Motor Shield and a 200 ohm potentiometer

Hi!

I'm having trouble to read the voltage value of the potenciometer's wiper "leg".

I connected it to the 5V-GND of the Arduino, and connect the wiper into A0 analog pin. At 100ohms, I should have read 2.5V, but instead, I got 0,49V! I'm using Matlab instead of IDE. I set the A0 pin in two different ways to see if it was a syntax error :

pinMode(A0,'input') and pinMode(14, 'input'); potencmt=a.analogRead(0)/1023*5

but none worked as supposed.Therefore, I connected the Arduino's 5V to A0 to see if I would get 5V, no problem. But with the potentiometer it's inconsistent.

Do I really have to set A0 as input(I believe I dont) in order to "tell" Arduino to increase its impedance? Do I need to use any special potenciometer functions to read the values?(I believe I dont either)

This is the script I have been trying to run:

Function motor

a=arduino('COM3')

a.pinMode(12,'output'); %DIR A a.pinMode(13,'output'); %DIR B a.pinMode(9,'output'); %BRAKE A a.pinMode(8,'output'); %BRAKE B a.pinMode(3,'output'); %PWM A a.pinMode(11,'output'); %PWM B a.pinMode(14,'input'); % ??

b=0;

while(b==0)

a.digitalWrite(12,1); % a.digitalWrite(9,0); a.analogWrite(3, 255);

pause(5);

potmcmt=a.analogRead(0)/1024*5

a.digitalWrite(9,1); pause(5);

a.digitalWrite(12,0); a.digitalWrite(9,0); a.analogWrite(3, 255);

pause(5); end end

But the values returned by a.analogRead(0) don't correspond to the ones read by the multimeter