A hard drive crash, and some other happenings that aren’t entirely clear to us, led [Devbisme] to put in a parts order. As he wanted to make the most of his shipping costs, he decided to fill out the order with parts that he’ll use eventually. He’s been working with surface mount designs and wanted to move from using resistors with 0805 packages to the 0603. Having nothing on hand, he devised a way to account for almost all standard values with the fewest number of different resistors.
That’s a mouthful, but what he actually did was figure out what combinations of resistors can best be wired in parallel to achieve a different standard resistance value. This way, if he doesn’t have a specific value he can solder one 0603 surface mount resistor on top of another one to get there. He ended up writing a Python program to best calculate this set of values. It came up with a set that lets him synthesize 159 of the 168 standard resistor values within +/- 4% using just 19 actual resistor values. His method requires anywhere from one to three resistors to get to each value. Soldering three 0603 packages on top of each other might not be the most fun, but it makes for easy parts inventory management.