Homemade PCB (Etching)

The Theory
           The LM317 uses a voltage divider circuit for feedback which then defines the constant output voltage for the device. The circuit seen below is straight from the datasheet for the standard use of the device. C2 is the only thing omitted in my design which was a bit dumb on my part.

LM317 Theory

           When you change the resistance in the 5k variable resistor the output voltage changes as that resistance changes. Again, this is due to the voltage divider present in that circuit.

A Simple Formula

           When all else fails, you can also use the pyroelectro LM317 Calculator. It makes life easier, for when you don't have a calculator handy.