775 spindle tachometer housing

This is an optical tachometer addon for a 775 motor CNC spindle (ER11), attaches by 2 M4x12 Allen screws . You only need 3mm IR LED and a 3mm photo diode, 2 resistors, arduino and a display. Programs for arduino can be found online, can also provide my own in case of interest.
The er11 chuck is reflective, so I covered most of it by a black tape, so the revolutions get detected.
One possible side benefit - the motor vent holes are not facing bottom, where the most dust is coming from, but the ait intake is rerouted to the sides. Not sure if it does much, though.