RADMON is a small, low cost and low power instrument developed for the Aalto-l student satellite. RADMON will measure protons (10-200 MeV) and electrons (0.7-10 MeV) in low-Earth orbit using a silicon detector and a CsI-scintiliator with photodiode readout. The instrument, the sensors and the electronics are described in this article. RADMON uses FPGA logic to analyze the continuously digitized sensor data at 10 MHz. We expect the instrument to be much faster than traditional radiation monitors with analog pulse storing. Fabrication of the electronics is now completed and the testing has been started. RADMON will be integrated into the Aalto-l satellite in the summer of 2014. Educationally RADMON has been both rewarding and difficult: half a dozen master's theses have so far been completed within the project. On the other hand there have been significant delays and continuity problems in RADMON due to the changing workforce.