BIGTREETECH SKR v1.3 doesn't have enough voltage for endstop

I started to assemble my delta printer today and only find out that the sense voltage on X+ X- and Y- endstops are only about 3.1v where the Y+ Z- and Z+ are 3.3V
so my X is always TRIGGERED or OPEN (depends on the marlin config) and it won't change.

I tried to replace the 180 ohm resistor on the optical endstop with a 100 ohm and I also tried to add a 220 ohm resistor on top of 180 ohm per the suggestion in a facebook group,
but none of them worked, and now I am clueless what approach I can still try.

I can't be the only one that having the problem, so I am wondering anything I did wrong?
appreciate for any input.

I had a similar problem with an MKS SBase and Lerdge optical endstop's a couple of month ago. I put a 1k between signal and ground to archive a proper low level as it was way too high (about 1.8V).
Maybe it's also this issue.

... for longer sensor cables I'm level-shifting the 3,3V or 5V signals to 24V and adjusting the return with a resistor bridge to the "original" voltage level ... this is good enough for some ten meters cabel elngths

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

It should be possible to get the endstops working by reducing the IR LED series resistor. Duet users sometimes face the same issue, because the open source optical endstop designs were not designed with 3.3V electronics in mind, and I am not aware of anyone not being able to resolve the problem in this way.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].