Tropical Africa, hmmm. I wouldn't have thought that Electicity supplies would be in abundance out in tropical Africa, and obviously in order to be in a position to use electronic items in the first place, you would need an electricity supply. It would seem fairly logical to attempt to provide an electricity supply local to places where electronic items would be used in tropical Africa, so maybe you could design some kind of power supply for the region? I believe sunlight would be plentiful there, provided no trees shelter the area, so you could do a solar based power supply. Alternatively, a local river could be used as the source for an electricity generator.
Other than that, I can suggest some kind of climate control based project. Tropical Africa can be a harsh environment to live in, and it'd be ideal to have a climate controlled home for anyone staying out there for any great deal of time. You could base the project on monitoring the ambient temperature and altering the speed of fans or other cooling techniques within the home/base.
Or, what about some kind of weather prediction project? The weather can change dramatically in tropical Africa and this can be a problem. Design a weather predicting device based on monitoring the current air pressure, things like that.
Hope this helps