BLtouch with RAMPS 1.4 never trigger z-min endstop

I'm installing BL touch sensor for the first time, its a clone from aliexpress, everthing are working well except the fact that z-min probe never change state either open or trigger.


I'm able to put pin down and up using M280 P0 S10 and M280 P0 S90. But in every states of pin up/down the status remains the same. I've already use multimeter to check continuity for this 2 wires and never got continuity signal so that means the state of switch was always open?

Should be able to read the closed state of the button when the pin is on top or bottom rifgt? I know that some BL touch clones have the logic in reserve way, and thats is okay. My problem is I never saw any change in state.

Could anyone help me with this question?

You cant read a bltouch with a meter or M119, It sends a tiny 5 ms pulse, it doesn't hold the signal like a switch or other probes
You would need a oscilloscope

from [locxess.de]
"NOTES M119 can’t be used to see the state of the sensor end stop as the signal is only 5ms long (A CRO might work)"

Or just move Z way up, deploy the probe and tell it to home Z, then manually trigger it and check it stops Z (while being prepared to remove the power should it not stop)

Edited 2 time(s). Last edit at 10/25/2018 01:24AM by Dust.