A mechanical boy made of 6,000 parts sits at a desk and writes any text up to 40 characters long. The message is programmed by arranging a set of cams (shaped discs) on a central spindle.
Three separate cam systems control the quill's X position, Y position, and lifting/pressure. As the main drive wheel turns, the cams translate rotary motion into the precise movements of writing.
The original automaton is preserved at the Musée d'Art et d'Histoire in Neuchâtel, Switzerland, and still functions after 250 years.