Black Box Probe show closed loop before touching plate

did you try the other clip on the bit? in other words, swap the clip wire for the plate wire.

 

That changes the logic (react to logic high or logic low on the signal pin, but still same pin) - wiring swop changes the actual polarity.

Confusing though, you want the Spindle body EARTHED (mains earth, to trip GFI) not Grounded (V-/GND/0vDC), they sound almost the same but are very different things. If your spindle body is tied to logic GND, all the EMI from the motor is getting dumped into GND on the controller!

 

that is exactly the issue, your spindle (clip on the bit) is now controller GND so clipping the sense wire to it will always close the loop. by clipping the GND wire to the bit it can now only sense when it hits the plate which is now the actual sense pin connection.

 

measure if Earth is connected to GND (Bad!)

 

It is weird for sure, normally PC components dont have GND connected to earth! Very old monitor? (the last 5-6 I've owned all had DC power bricks, havent seen a monitor with onboard AC in like a decade or more)

 

This issue has been teasing my mind for a bit. I really don't want to connect a microcontroller pin to the spindle nor to a random bit of metal that could end up anywhere on my desk, including contacting other bits of metal which may or may not be connected to 'something'.
Then there is a ground loop thing we all want to avoid.
And then there is the knowledge that optocouplers can vastly reduce noise problems on limit switches, so why not use on on the probe as well?

So I grabbed a couple of paper sensors harvested from an old photocopier. These have an optocoupler with a gap that is occluded by a plastic lever.
The lever makes the sense distance too long for a probe, we want the actual probe thickness to be minimal because most of our machines have limited Z travel.
I cut off the lever and modified the rest of it to have a short lever. This ended up 12.8mm thick and worked but was sensitive to bit position and size. Not what we want.

I started again and end up with this: I removed the sensor from its plastic base and discarded the lever. Glued it to a plastic card and then built a new lever.
But using a long flat lever like this we can minimize offset errors caused by the diameter of the tool. this triggers within 1mm of this resting position, thus minimizing the offsets even more.
aim the tool at the black dot on the icecream stick and probe...



The lever detail, the lead weights are to keep it where I put it otherwise the wires will move it at the worst possible moment. It is important that it is held flat.

By having a relatively long lever arm one creates a nearly linear movement of the sensed end, thus removing the radius errors one gets with a small radius arm. Hit the black spot with a cutter flute for best calibration.

The experimental wiring... I am using a bare Arduino Uno for my controller and this is a plug in 'screw shield' that gives me quick access for this experiment. I will make a more permanent connector in due course.


I figured out the wiring using sites like this one Making endstops from printer photo interrupters. ending up with a 150 ohm resistor (the blue one in the photo) from power to the LED, and a 10k from power to the output line.

Some optosensors have a very narrow gap, I used a wider one to make it easy to build my lever though a narrow gap is theoretically more accurate.

NOTE: the output from this sensor is always on (acting as a NC switch) so you have to invert the probe sense. $6=1
EDIT: I have since reconfigured it to normally off by remaking the the part that breaks the beam in an L shape. Now it operates with $6=0 which matches my other probe, a PCB with a clip for the tool, also has an opto device to prevent false triggers.

Once you have it working you need to figure out how high it is. I set the offset to 0 then probed, removed the sensor, then jogged down slowly until my favourite bit of paper was just touched by the tool.
At this point my z was at -9.7mm

My paper is 0.1mm thick so I could add that to the 9.7 to get 9.8. When I put that into the probe wizard the tool ends up at the right spot for Z=0 at the surface of the work.
I may refine this value after some experience with actual work.

 

That can be added in a future version, added to todo list Probe Input endmill diameter in inch or mm · Issue #126 · OpenBuilds/OpenBuilds-CONTROL

Use a straight shank / piece of 1/4" round bar / known diameter to establish Zero then switch to the Tapered bit and Zero Z only

 

DC gnd to Earth leakage via the new monitor? Disconnect as a test

 

ah, you have an XYZ probe, so you cannot switch the wires.
So, as Peter said, you now have a DC ground to power ground connection via that new monitor and you will have to figure out how to isolate it.

 

How old are your switches? Your suggestion has been implemented a while back

 

i remember plastic washers with a little step in them that were used for mounting TO200 transistors to heatsinks, could those be used on the limit switches?
ah, still available
https://www.aliexpress.com/item/33043457451.html?gatewayAdapt=Msite2Pc

 

Its wasn't a plated hole, so you don't need the shoulder - screw side has always been isolated, but the bottom pour was exposed. Pulled that back in the 2nd revision. Was only issue if switch was mounted upside down (which sadly some of our build videos do). The intended design has the rubber pad on that side to space the switch pins away anyway, and when mounted right way round the screw head sits on the unconnected cover plate

 

Yeah, that was fixed since in the V1.2 switches

 

It should be there: (Next to the hole on the main board) - if not its an old rev. Big warehouse, old and new stock tends to float around.