If you want to control devices and/or take measurements from sensors which are not necessarily in close proximity to your PC, you should consider a distributed control system. This is one of the main aims of our "Control Master" range of boards. You just need one master controller board connected to your PC via a USB lead and then you can add a range of "slave" control boards for a wide range of controllable devices. This includes DC motors, relay control, analogue measurements (eg temperature, pressure, light etc...) and a million other purposes. All slave boards are connected to the Master by a simple single pair of inexpensive wires. What's more.... they can be up to a massive 1Km from the Master. It uses RS485 communications technology to provide control for up to 30 boards, all connected to the same twisted pair wires, and spread over 1Km. These are very often used in commercial and industrial applications where robust operation and PC electrical isolation are important considerations.