Electron beam evaporation sources require two power supplies, one each for the filament current and the electron acceleration. To obtain a stable deposition rate, the emission current between filament and target must remain constant. During film deposition, slight geometry changes in the evaporator cause significant rate variations, making constant readjustment of the emission current necessary. While in commercial solutions, analog feedback regulators are often used to perform this task, these controllers cannot easily be adapted to home-built evaporation sources. The microcontrolled feedback controller presented here is more flexible and versatile than the commercial solutions. The controller can be easily modified to work with different external power supplies and allows the easy upgrade of most existing electron beam evaporation setups. A serial-port computer interface completely integrates the controller into the automated laboratory environment.