I wish to connect both a probe and a toolsetter to a generic Chinese parallel port breakout board. Linuxcnc and indeed gcode use a single probe output.
The pin I am using requires to be grounded on probe contact. The tool setter is a simple switch to ground, however the probe's normal output is high (5v) going low on contact. The toolsetter is permanently wired whilst the probe is plugged in when required.
Given that the devices are used seperately this should not pose a problem with both wires connected to the same pin. However, if the toolsetter was accidentally pressed during probing, or the probe was accidentally left plugged in during tool setting, then the 5v probe output would get shorted to ground.
My question, therefore, is how to prevent this accidental short. Perhaps a diode in the toolsetter ground wire?

 

Welcome to AAC.

I would put a toggle switch on the input so that only one or the other could be connected at a time, isolating them from each other.

 

Certainly a toggle switch is one way to go, and it would work. But my suggestion would be one single point to plug in EITHER the probe OR the tool-setter, so that when one was being used there will be no chance of a false signal from the other. NO, it is not convenient, but my experience with machining is that one mistake and start over. THAT is A WHOLE LOT LESS convenient.

 

I agree, just looking for fail safe and convenient. My initial thought was for a single plug because a toggle switch is too easily forgotten.
However, there must be solutions for a permanently wired tool setter, since there is only a single g code for probe and most toolsetters are permanent fixtures. Hence my electronics solution question.
I also can investigate modifying the M6 g code, that calls for toolchange, to operate a change-over relay whenever that's called.
In my experience, if anything can be forgotten, it will be at some time!!!

 

OK, my suggestion would indeed require a modification to "permanent wiring already in place." No question about that. It would certainly take more effort to install.
So that decision is up to the TS. I explained the reason for it already.
In addition, installing a selector toggle switch for an "either-or" selection will require the same amount of effort to revise the same connections, because it will require opening the same circuit to the tool setter..