Data logging is the process of collecting and storing data from an experiment. Traditionally, data from science experiments was collected manually by hand and graphs were produced using pen and paper. By the introduction of cheap and powerful microcontrollers, all data logging operations are currently carried out using microcontroller-based data logging devices. This article describes the design of an educational microcontroller-based data logger device, which can be used to collect and save data for both offline and online analysis. (C) 2009 Wiley Periodicals, Inc. Comput Appl Eng Educ 18: 397-405. 2010: Published online in Wiley Inter Science (www.interscience.wiley.com); DOI 10.1002/cae.20281