I am in the process of completing a 3d printer, reprap style. I am remotely controlling this with octopi software but find it would be useful to be able to leave the octopi server running (rpi) whilst being able to control the power to the printer and camera from a browser terminal. In order to do this I will need an interface card for the rpi. Most of these seem large and clunky. I just wanted one which will not increase the overall size and yet give good visual indication of the output states. I have made two designs, the std transistor type where the load is connected to the supply and switched to ground, and a design where the load is connected to ground but can be switched high. This will be useful for powering up usb devices, like the camera. Details and artwork are in the pdf.
Hopefully this will be of use.