Used a potentiometer to control the servo.​ The connection might be a little loose.


Then, I followed this tutorial to control a continuous servo and applied it to a magnifier. It should be getting slower when it approaches ​90 degrees and then change its rotation direction. However, it seemed a bit of out of control when I rotate the potentiometer fast - not so fast actually. It could only act in the correct way when I rotate it very slow.


Then, tried the Force Sensing Resistor. During the process, I accidentally unplug​ the wire connected the ground pin to breadboard and took a long time to sort out the problem - doubt almost everything... such a stupid mistake...