In many cases you simply need a voltage source that could be used right away. It may be 5V, 3V or other like. Many battery operated electronics require voltages that are multiply of 1.5V – single cell. So for instance if device requires 4 AA batteries then it total voltage is 6V. Jason is a fan huge of garage sales where he can find lots of ideas and materials for his projects. But he wants to make sure if devices works properly before purchase. Due to variety of battery types he didn’t want to carry a bag of batteries around. So he came up with nice idea p DIP switch controlled power supply. As you can see there is nothing actually new or extraordinary. An LM317 power regulator is used to adjust voltage to right level. DIP switch seems to be convenient way of selecting the voltage. Each switch is connected through resistor that allows adding 1.5V per step. Supply is powered from 9V battery. So this makes useful battery replacement. Output wires have alligator clips to connect to device being tested. I think DIP switch idea can be used in breadboard power supply as well, so you could generate proper voltage for embedded project prototypes.