I take it what we are talking about here is the probe facility.
In the computer, whatever pin is allocated to your probe is normally kept high (5v) by the internal resistors in the computer. On the CNC4PC Bob board Arturo has seen fit to reverse these - so by the time you see the pin at the Bob, it is showing 0v.
Check that and see if I am correct - I think I am but I am not sure.
If you are using a copper clad pad, or similar as your touch plate (connected as you seem to say to pin 13) then what you need to do is put a +5v signal to it - not ground (0v) - why mess about with resistors.
Just try this with the diagnostics page on, and, if you touch your pad with a 5 volt lead, you should see the Digitise LED light up.
If it does, then all is working.If it is on then goes off, reverse the "Active Low"
You now have a dilema.
I personally would make an insulated probe of a fixed length that I can put in my chuck, with a +5v lead to it and use it that way.
However, what Arturo is saying is that you need to bring the plate up from it's 0v base to +5v (i.e. it is "on" all the time) then reverse the settings on Ports and Pins to active high - so the computer thinks it is off (because the computer sees it as low) . To do this he is suggesting putting the 5v to the plate through a 220ohm resistor. What would happen then is the tool comes down (and we must assume the tool is at 0v), touches the plate, pulls the plate down to 0v and gives a signal to the computer like that. It is one of the drawbacks of the CNC4PC board.
What I would do (which is even simpler) - and which I have done on mine - is take a lead from pin 13 BEFORE is goes into the Bob electronics, if you can get to it. Take this to a small socket on your electronics box.(a mini jack plug will do). Make up your plate with a wire and plug to fit the socket, so that when you want to use it, you can plug it into the socket and put it in position on your machine. Bring the tool down (which is normally at 0v - although check there is a return path) touch the plate. This will register, then you can move the tool up and unplug the plate.
Using the socket ensures there are no loose wires floating around when not in use.
Hope this helps.
Jim Pinder