Well if you work with electronics as I do, you’ve probably noticed that every electrical device works on different voltage. Until now I was forced to use batteries or different types of supplies. With this regulated power supply you can easily change voltage from 1,25V to 13V by turning potentiometer. Only thing that you need is an adaptor that gives more than 13V (mine gives 17V). Heart of this project is LM317T voltage regulator, which is very good. Reason why this adjustable voltage regulator is so good, is that this regulator is small and it can regulate up to 40V and up to 1,5A so for desk power supply is this regulator best choice. Here you can see some pictures and the circuit. You can also make this as a fixed voltage regulator there’s an equation for counting resistor value (note that R1 has to be 240ohms).
If you want to calculate output voltages use this equation:
VOUT = 1.25 * (1 + R2/R1)
And if you want to calculate resistor value use this equation (with potentiometers R2 is maximum I’ve used 2K2 Potentiometer):
R2 = R1 * ((VOUT/1.25) -1)