This article reports on the training of a blind foreign language teacher of sighted students and the designing of a substitute of the board. A composition of computer devices available today was provided to the blind teacher in order to get pieces of writing projected on a screen. This basic instrument was transformed through instrumental geneses (Rabardel. 1995) i.e., transformations of the blind teacher's activity and/or of the properties of the artefacts in order to get writings readable for sighted students as well as adapted to didactic purposes. The article deals with knowledge construction, which implies four categories of actions on pieces of writing: adding, erasing, organising and pointing to. The questions involved are: how can a blind teacher manage these various actions? What are the limits of such instrumental geneses? (Contains 1 figure and 1 table.)