This is a board to connect the limit switches of a CNC machine or a 3D printer.
It offers noise reduction and galvanic isolation between the limit switches and the mirocontroller.
There are 3 photocouplers (one for each axis) and a 5V to 5V isolation module. The NPN transistors on board are used to invert the signal from the photocouplers and light an LED every time a limit switch is triggered. The NC and the COM pins of the switch are connected on board. NO is not connected. If you use 2 limit switches for one axis they should be connected in series.
You can buy a bare pcb and build one for your machine.
This is an open source project and you can download for free the gerber files to produce a pcb on your own. An interactive BOM is available here.
Enter your email to receive the gerber files.