servo control using potentiometer

[mongkiosk]

hello guys
i am going to do my final year project regarding the servo control
basically,i need some guides to do it
i need some guidance how the potentiometer can control the servo rotation respectively by rotating the potentiometer probe
i've been watching some videos on youtube where got some people already succesfully do it
so I really appreciate if someone can help me in this
roughly,i am going to do it using 8051 as the brain and for sure i need adc to convert the continuous signal from the potentiometer to digital signal
thats the only basic thing i know
really need some guidance from some experts here
thank you very much~

 

[ngmedaboard]

I'll give you a very top level answer to this. The potentiometer is used for feedback and will vary in resistance depending on the position of the servo. Thus you will be able to associate a specific resistance to each angle the motor is turned to. By applying a constant voltage or current across the potentiometer and measuring the other you can determine the angle of the servo. Generally one varies the voltage sent to the servo using PWM, the resistance varies depending on the position of the servo and the current is then measured by a circuit that either allows the rotation to continue or limits it.

This applies to non continuous rotation servos and the principle is slightly modified for continuous rotation. My description is a little weak but I think I've presented the basic idea. There's a forum on lynxmotions website about building a servo from a gear head motor and a potentiometer that you may find useful. I didn't have much luck finding a schematic of how one works, but you could probably pull a $10 servo apart to learn about it.

http://www.lynxmotion.net/viewtopic.php?f=26&t=3399&start=0

 

[wade_hassler]

Are you describing a system to make a servo-motor duplicate the movement of a potentiometer? If so:

Implement two timer-interrupts
   Timer A triggers every 15 milliseconds, turning ON an I/O pin that connects to a servo-motor. 
       Also reads the ADC
   Timer B is started by Timer and triggers at a variable time (minimum 1 mSec) later, turning the same I/O pin OFF. 
       Also starts an ADC-reading

An (8-bit) ADC reads the position of a pot connected between Vcc and ground, giving a number 0-255. This number is multiplied by 4 and added to Timer B's minimum, making its output in the range 1 to 2.0+ mSec. This will cause the servo to rotate proportionally to the pot. Unfortunately, the pot's rotation is 270 degrees and the servo's is likely to be 180 degrees, but if have gotten that far you will by then see what to do next