[BUG] If I start the spindle, ALARM:13 is displayed about ucnc

[Paciente8159]

If this only happens when you run the spindle...most probably it's not a bug but a noise issue.
If you can run GCODE ok and nothing goes wrong and when you turn the spindle on it trips an alarm now and then you have a noise issue.

You can confirm this by running the same GCODE with the spindle unpowered (but still using M3, M4 and M5 commands) and nothing trips.

You can solve this with hardware. I recommend using some optocouplers (like the inexpensive PC817) and work with 2 voltage levels. 5V on the Arduino side (near the board) and 12V or 24V (or whatever power supply you are using on the other side (on the limits wires).

Here is an example:
https://planet-cnc.com/wp-content/uploads/2016/02/switch.png

I've also had this issue with my Spindle+VFD. The optocouplers solved it.

EDIT
Actually I use a circuit like the one above but use N.C. switches. That allows me to detect also unconnected limits or faulty wires.

[andy0983]

You were right, there are interferences with the Spindle+VFD and the relay that turns on the spindle cooling
Thank you for your help