I just ordered a micro-controller to get my hobby started, but couldn’t wait for it to arrive to get my projects rolling. I wanted to controll a servo using just the parts i had laying around, so i opted for a 555 circuit.
This circuit produces a 50Hz square wave with a duty cycle of 7.5% (this will set my servo to the middle position). To control the servo, the duty cycle must be variable from 2.5% to 12.5%, so i replaced R1 with a 3k potentiometer. Changing the value of this resistor only affects the duty cycle of the output, and not the frequency.
Here is a great illustration of what’s going on to control the servo: