This experimental circuit board was designed and built as a development aid for those constructors who wish to design their own parallel printer add-on boards. The author used the prototype board whilst experimenting with digital to analogue converters (DACs) and liquid crystal displays (LCDs) amongst other things.The board of which the circuit diagram is shown in Figure 1, connects to the standard 25 way ‘D’ connector of the computer’s parallel port via a 25 way ribbon cable, and is terminated on the circuit board with a transition connector (see the relevant construction notes). The design itself comprises of three circuits — one for each of the registers (DATA register, STATUS register and CONTROL register) associated with the parallel printer port.