Also a good starting point for novices wanting to get their hands dirty with the 555 timer IC. Some would argue that this is not the most efficient approach, but hey (read the title), it's simple, and it works.
Check the video out.
More images and description here.
Pulse Width Modulation (PWM)
Put simply PWM is the process of switching power ON and OFF to a device in pulses at a specific frequency. Same approach used in commercial light dimmers, DC motor speed controller, CPU fan speed controllers and etc.
That's what we seek to achieve here.