if you are going to use ULN2003 or some similar IC for controlling a stepper motor then take care the necessary digital value gets inputted based on the movement of the joystick....
specify somemore details about the joystick specs and the design you want to design... if possible about what your venture is and what the desired output is for an particular input.....
because based on the transducer you are using as joystick only your design can be done....