For most people, making coffee entails taking a couple scoops out of a can of pre-ground coffee, adding water, and pressing “Go” on the drip machine. To others coffee brewing is an artform, and want as much control over the process as possible. For those without an overflowing bank account for a home roasting machine, Evil Mad Scientist Labs have put together a general guide for throwing together a Coffee Bean Roaster and cooler (which is apparently just as important as roasting) from a low cost hot air popcorn popper. The home roasting scene is even big enough to warrant its own Wikipedia page, which also mentions using a popcorn popper as a bean roaster.
The guide includes some great simple circuit diagrams to keep in mind when hacking your own, as well as a good explanation why you shouldn’t just clip out the heating coil for cooling mode.