555 Servo Controller
From BEAM Robotics Wiki
This 555 circuit is an easy way to control hobby servos. It has a continuous variable input from 0-5 volts and can be driven by a wide variety of circuit inputs to include the BEAM bicore, microcore etc.
An easy way to experiment with this circuit is to use a signal generator so that you can input a variety of waveforms (such as a sine) and play with the DC offset, frequency and amplitude and see how the servo reacts.
A single transistor sine oscillator as an input with the 555 circuit can make a simple walker. A couple of photo cells as a voltage divider and summed at the input can make a light following photo walker. This is called an OISM (Oscillating Infinite State Machine) which is a branch of Neuromorphic robotics (BEAM is a separate branch but it all follows the BEAM philosophy).