Manual tool change + tool lengh touch off

It could be electrical noise. Exactly how is the switch wired, and to what?

What does the probe signal look like in Halscope?
If you are in the axis UI then it is Machine -> Halscope.

image missing http://www.linuxcnc.org/media/kunena/attachments/legacy/images/Bildschirmfoto_2-b54cb913e80d1d85edaa3643a645f4dc.png

I can't imagine that it's electrical noise, because in this picture my power stage is not enabled and i build an RC lowpass with 1kHz corner frequency. This signal is about 3kHz. And why is there no electrical noise if the switch is open?

Ok i found the reason, my paralell-port has internel pullups, so if my switch was closed there was a current backwards through my lowpass causing 1,8V drop, an thats no clear signal.

EDIT: G38.5 works fine

How can I set the direction of G38.5 Z0 f15?

EDIT: Ok found it

You could probably remove the lowpass and use the "debounce" function in HAL.
www.linuxcnc.org/docview/html//man/man9/debounce.9.html

I think that probe moves towards the indicated position. You might need a G53 on the same line as the probe command.

Where do I have to add the debounce command and which are the right parameters for
"parport.0.pin-10-in-not" ?