Here’s a simple project with Windows control software that allows you to control up to eight relays or other actuators, and read back an equal number of input lines, all by means of the parallel port on your PC.The UPIO software and hardware (a board attached to the PC’s parallel port) allows you control up to eight relay outputs using a Windows-style user interface designed for user-friendliness. UPIO also allows you read back logic states on input lines.Circuit descriptionThe circuit that belongs with the UPIO program is very simple and consists of a few low-cost and easy to find parts. The circuit diagram is given in Figure 1. A tristate buffer type 74HCT241(IC5) arranges all input contact reading. An 8-bit latch type 74HCT574 (IC3) is used to preserve the output state during instruction execution. The third essential component is a power driver type ULN2803 (IC1) which enables output relays Re1-Re8 to be actuated and de-actuated.