I wanna build a laser, the problem is for the last stage of kinematics, there is a need for cables to be tight, therefore I thought to connect masses of mechanical end-stop (3 pins: switch, +vcc, gnd) to the ground of a 24v fan (2 pins: 24v+ gnd), is it doable?
Are you wanting to reduce the amount of cable going to end-stops [or fans] by connecting the end stop gnd to the fans gnd?
yes, that’s exactly what I want.
In theory, and statically, a gnd signal can be picked up from any gnd wire as long as they both were originally wired to the same electrical gnd on the motherboard. You can verify this with an ohmmeter.
In practice, and dynamically, it is better for remote sensors to be individually wired from the motherboard to the sensor and back with discrete wiring. This ensures that the source and return current is only that of the sensor.
When a ground wire is shared all of the return current for all the devices on that ground will be seen by the sensor and its processor input. So in this case the fan current and sensor return current are seen by both. The fan does not care but it’s possible for the endstop circuit to pick up ground shifts created by fan motor noise.
Endstops are notorious for picking up noise in these systems, especially motor and laser firing noise because most processor inputs have little isolation from radiated and conducted noise. The longer the sensor wiring the more susceptible.
I note that the DLC32 has input filters on its I/O so that helps.
The above is a long-winded way to say. Your mileage may vary depending on the specifics of your configuration which include ground loops, wire length, proximity to motors, and other sources of noise.
If the return is greater than the risk give it a try.
Test the configuration with as much stress on the system as possible. Problems from ground shifts tend to occur when lots of artifacts in the system are turned on at the same time.
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I hope you have already verified that the fan gnd is not a controlled signal through a FET. Often the ground side of this boards is what’s switched/controlled. The schematic for the board should show you if the fan connector gnd is a solid ground or a switched ground.
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Looks like the fan is plugged into a dc power socket. I would imagine that is not controlled.
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