An opto isolated FET switch for driving a heatbed, fans and anything else on an alternative power supply. It has a constant current input so it can be driven direct from a processor output or 24V output with no problems, The design source files are eagle PCB. It is single sided so it can be milled using the printer. This is a single sided design that was milled using the printer. Electronics BOM is in the eagle file. The enclosure has retaining bumps inside to hold the PCB. The lid is friction fitted. Add some M5 nuts and bolts to attach it to the frame. Alternatively use the slots in the lid to zip-tie it to the frame. As standard, you get the openSCAD parametric CAd file so you can resize the box to anything you like. Note that the pictured driver is for controlling the electronics cooling fan. The power cabling is smaller than the cabling used on the heatbed driver. Happy Hacking - Matt