Home is Where the Heart is…

Finally figured out the home switches.  It turned out to be pretty simple once I got moving on it.  There were three wires coming out of each optical switch.  After probing around, it was discovered that:

Purple was +5 volts

Yellow carried the signal, either high or low of the switch

Black was connected to ground.

These connections were found by carefully piercing the the insulation of each of the 3 wires with a sharp stick pin and then probing with a continuity meter in the wiring box to locate were the connection came out.  Once the associated screw terminals were located, it was pretty easy to use the ohmmeter to find the pins on the parallel port connector.

Since I could not get at two of switches with the stick pin, I had to start up EMC and move the axis to limit, then unplug the parallel cable and verify which signal had gone low.  Turns out the switches emit a high 5volts when unblocked or open and a low signal ground when blocked or closed.

After I knew which pins went to which signals I had to open the parallel cable and connect them to input pins on the computer side that were still available to be used with EMC.  My probe was a straight through connection on pin 10 so I connected the XYZ home switches to Pin 11,12,13.   This leaves me with just 1 more valid input pin under EMC.

Since I still don’t quite know enough hal to add the pins myself, I used stepconf to generate a bogus config file with the home switch pins.  Then I cut and pasted from that file to my real hal file.  This trick allowed me to use stepconf, without blowing away my hard won spindle settings that were manually added into the original hal file.

It took a bit of tweaking with search speeds in the INI file but it was pretty quick to set up and now, wow!

Homing an axis is really quick.  Set up is much simplified as I can home each axis, then move out to the work and “touch off”.  I set up soft limits in the config file and no longer have to worry about driving off the axis end point.  I am now able to drive the machine around at fast speeds without fear of crashing.  This is helping me realize what kind of feed rates I can actually achieve.  sPlendiD


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