This is on a machine that has been working fine for years. (and still is working fine.) I'm just a little baffled by how the 12v+ is floating right at ground, and the 12v- is -12v below ground. I did a little more poking around, and tried to check for current between the DC- and ground and the moment I touched the probe to the DC- to ground Linuxcnc pops up a bunch of errors about the Mesa card having an over-current, and shutting down. I need to go back and recheck everything and try to see where i went wrong when I set it up years ago.
However maybe having the DC+ floating at ground level might not be an all bad thing, I can then connect the 12v+ to the spindle tool clip, and the touch plate to the input. With a conventional DC- ground would I need to set up with a 12v pull up resister to the input and then to the touch plate, and a ground wire clipped to the tool. (Assuming I can figure out why my 12v is below ground instead of above it, and fix it.) ----- Original Message ----- From: "John Thornton" <j...@gnipsel.com> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Sent: Friday, April 7, 2017 4:52:03 PM Subject: Re: [Emc-users] 7i77 Field Power? This should clear it up. http://gnipsel.com/linuxcnc/configs/7i77.html JT On 4/7/2017 3:47 PM, Todd Zuercher wrote: > I was going to start working on putting a tool touch probe on a machine with > a Mesa 7i77 setup. > (I was just going to try a wire clipped to the tool and a touch plate for a > start.) > I pulled out the multi-meter and started poking around to try to figure out > what exactly I wanted to do and noticed something odd. I checked the V+ to > ground and it read 0v and V- showed -12v. > My field power is suppied by a simple 12v switching power supply (wall wart). > I don't see any obvious place where the 12v power is referenced to ground > (positive or negative.) Might this be normal? Would It cause a problem if I > tried to connect the V- to ground (such as short out the 12v power supply)? > Is this a symptom of another wiring problem somewhere (a short to ground > hidden somewhere.) > Which side should I use for the spindle/tool wire clamp the field power or > the input pin? (the spindle does show a little resistance to ground) > Should I put any resistors in line to help protect from short circuits? ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users