Mars 3 Print Complete Sensor

It annoys me that I can't use Octoprint with this printer, but this way I can at least get notified when it finishes printing.  This has two brackets that attach to the Elegoo Mars 3.  One attaches to the top of the z-axis tower and holds the sensor body, the other slips on to the moving arm and holds the magnet that triggers the sensor.

In addition the printed parts, you'll need a suitable door/window sensor. I used this one that is a 20 mm cylinder.

You'll also need a pair of M4 heat set inserts and a pair of M4x14 or M4x16 screws. The magnet holder has a hole in the bottom for a screw to keep it from sliding. You may not need it, but if you want to include it you'll need an M4 screw that is at least 26 mm long (because the arm isn't actually a rectangle, the bottom side is hollow). I used an M4x30 and it works pretty well.

Installation

To install it, remove the two M4x10 screw from the top of the z-axis, add the bracket, and put the M4x14 or M4x16 screws where those screws were. You can then use the M4x10 screws that you just removed for the little bracket that holds the little retainer in place.

I have the sensor hooked up to Home Assistant so it can send me notifications and automatically turn on the exhaust system to pull the fumes from inside the printer.