Optical Home Switch circuit design - feedback requested

[mhackney]

Hi all, I normally spend my time in the Benchtop Machines forum. I am just wrapping up conversion of a Grizzly G0704 and wanted to use optical switches for combination home/limit switches. After searching, I did not find any info on circuits to do what I wanted so I came up with this.

My objective was to use Optek OPB830 optical switches as home switches wired to a single pin on the BOB and in Mach 3. This conserves pins since Mach3 homes each access in sequence (there is no advantage to having each home switch wired to its own pin). I also wanted to mimic the behavior of a mechanical NC switch circuit, i.e. there is normally a +5 volt on the line which drops to 0 volt when the switch is triggered. If used for combination home/limit this will trigger a limit if a wire to one of the switches breaks for instance (a little extra safety measure). Since there were extra unused components in the ICs used, I was able to add a 4th optical switch that I can either use for an ATC home switch or maybe as a spindle tach. It is highlighted in yellow in the circuit diagram, simply omit V04, R7, R8 and connector A.



I plan to put this circuit in a small box mounted on my mill's column with short leads to each of the optical switches. A 4 conductor cable carries power, ground and the signals to my control box. I've been using these 4 pin connectors from Radio Shack and will likely use them on the connections to the switches and to the control box. (you need the mating plug too)

At this point, I've wired up the circuit on an experimenter's board and tested the logic. It works great.

Here is the prototype:

And a short video of it in operation:

Optical Home Switch Ganging For Mach 3 CNN - YouTube

Optical Home Switch Ganging For Mach 3 CNN - YouTube

Next I will build it on a protoboard and hook it up. I haven't drawn electronics in decades so please excuse me if the drawing sucks! Feedback welcome though. I've thought about milling a PCB but I have not done any CAD work on PCBs. I've tried both Eagle and DipTrace for the design but the learning curve is just too high for a one-off project like this. I was hoping to produce the gcode for the PCB and make it available for folks and maybe offer milled boards with the components (a kit).

cheers,
Michael

[Al_The_Man]

This is a variation on the same idea, it may need tweeking for different components.
Al.