This video shows a simple circuit that can be used to control the position of an typical remote control (RC) style servo with an analog voltage. The PWM (pulse width modulated) control signal format for an RC servo is reviewed, followed by the presentation of a simple circuit that can be used to control the servo with a simple adjustable DC voltage.
The circuit is built with rail-to-rail op amps and a few resistors and capacitors. Note that the schematic presented doesn’t include all of the decoupling on the power supply and reference lines that you would likely want to include. A description of the circuit, as well as a more in depth discussion of each of the building blocks such as an integrator, hysteresis comparator and DC signal conditioner circuit including an attenuator, inverting amplifier and level shifter, is presented.
For more detail: Circuit Fun: Control an RC Servo with an adjustable DC voltage