In this truly awful video, you can see my bench power supply at work.
For testing, I coded a function to cycle the voltage between 0-5.0V. In reality, 0-100% duty cycle is the parameter the code changes. A "PWM'ed" square wave(yellow trace) is fed to an RC filter, which is then buffered with an op-amp(the op amp output is the blue trace).
You can also see the LCD updating in realtime. The voltage reading is coming from the ADC on the ATmega 644. It's has a hard time keeping up with the displayed "SET" value, but there probably several factors, the biggest of which purely software related, I simply don't refresh the "widget" that displays the voltage reading any faster than 3Hz.
(Ignore the Amperage settings/reading, they're not coded yet, the analog portions of that have me the most intimidated)
Anyways, crappy quality aside, this is a great demonstration of how PWM signals can be used to generate analog voltages from a digital MCU pin, and how "duty cycle" affects what comes out of a simple low-pass RC filter.