Simple 555 Variable PWM Astable Oscillator

I came across this circuit the other while trying to make a simple open loop control system for driving DC motors and other non-feedback actuators. Another good use for the 555 chip is a variable PWM circuit that isn't that dissimilar from the regular 555 oscillator.

Familiar right?
See my 'Circuit Help Index' for help on 555 astables.

We can take the normal RC timing circuit and modify how fast the timer rises and falls as the current moves in different directions using diodes which are of course directional. Essentially controlling the 'mark-space ratio' of the oscillator through differing the RC constant in each direction.

We can make the circuit variable by adding a variable resistor in one direction, a good rule of thumb value for this resistor would be twice the size of the fixed resistor as you will be able to get a duty cycle range of around 0 - 70% or more if you increase the size of the variable reistor relative to the fixed resistor.

I hope you find this useful.