How do you make a simple Voltage regulator?

Answer 1

This depends heavily on the intended usage (voltage, power, etc).

If your power source already has the correct voltage but you want to regulate power spikes (e.g. electrical noise in a car), you can use a passive RF filter: basically, an LC low-pass filter element.

If your power source has a higher voltage than the device you intend to drive, there are two options: a passive regulator, built around a power resistor and a Zener diode, for very low to low power systems, and very low cost; or an active regulator built around a 78XX chip (or equivalent), for medium power systems, and somewhat higher cost. The 7805 chip is very widely used to provide 5V, and will always work. The Zener regulator is really the simplest and cheapest way to do it, but it requires you to modelize your power requirements to choose the correct diode and resistor.

If your power source has a lower voltage than the device you intend to drive, there are various chips available, but they generally require more external components like a coil and a capacitor, and require you to do more computations to get right. They also generally cost more.