Interlock circuits.

[mccarrot]

This is kinda similar as my latest desing, but I have added a capicitor and a pull up resistor to make the input more bullet proof.

[DMills]

Yea, I omitted the RFI protection networks and a couple of low rating polyswitch fuses in that sketch.

If you use a galvanically isolated supply for the thing it increases the protection against external shorts to signal lines, and actually this thing is best when run from as low a supply voltage as possible, so that the range of voltages that will bias both transistors on is as small as possible.

I was really posting to see what other people were implementing so I could make sure I was not leaving myself open to someones badly thought out splitter.

Regards, Dan.