I would like to connect the different ground wires of temp. sensor, end stop, hotend, and two fans to reduce the number of wires going to the moving hotend sledge.
I noticed that the ground pins on the Smoothie don’t seem to be connected (e.g. ground of hotend and endstop). What’s the reason for this and can I connect the ground pins together?
Thanks
Hugo
Smoothieboard v1 on a 3d printer
You can’t do that, for many reasons. For the temp sensors, the ground is “special”, it’s a reference, it needs to be left alone or you’ll have bad readings or even burn the sensors. For the other ones, you’re putting yourself at severe risk of generating EMI, burning things, etc There is a reason all machines, in particular pro ones, do not do this despite the obvious cost savings. It’s a terrible idea, pretty much.
Welcome by the way ! 
The mostfet which turns some load on and off is usually on the ground side (n-channel). So, the ground pin for the hotend isn’t always connected to ground.
Sounds like it is not a good idea to do that. Thanks guys!
I need to pick up on this. A friend of mine mentioned that the Smoothie has a common high, rather than a common ground. Would it than not be possible for example to connect the plus of both fans together?
It’s technically imaginable, it’s not recommended and not supported.