SKR 1.4 "PROBE" pin not working for BL-Touch

General Discussion
1

Basic Information:

Printer Model: SP-5
MCU / Printerboard: SKR V1.4 (lpc176x CPU)

My issue:

I am trying to hook up the sensor signal of my bl-touch to the SKR v1.4 “PROBE” pin instead of the Z-endstop pin. No matter what I do, the PROBE pin is low voltage. I’m suspicious that the klipper firmware has disabled the pull-up on the pin.

The PROBE pin is connected to P0.10 on the LPC1768. I searched the klipper source code for that pin, and see a hard-coded reference to it in i2c.c:

DECL_CONSTANT_STR("BUS_PINS_i2c2", "P0.11,P0.10");

Is there any reason that declaration would cause the pin to not go high?

The whole system works just fine if I put the bl-touch sensor pin on the z-endstop pin, P1.27.

Here’s the board diagram of the SKR 1.4: BTT SKR V1.4PIN.pdf

2

Any reason why you did not attach a klippy.log as requested?

3

Yes, sorry, I didn’t think it was relevant because the MCU doesn’t get good input, so the log wouldn’t show anything. I’ve attached the log to this post.

The only thing I change between working and not working is the pin assignment of [bltouch] sensor_pin (and of course the connections on the mainboard).
klippy.log (95.1 KB)

4

You need to add a pullup: sensor_pin: ^P0.10

5

Thanks, that fixed it.

Can you help me understand why that pin needs a pullup, but pin P1.27 (z endstop) doesn’t? Is there something in the klipper codebase that sets some pullups?

I’m asking because my next problem is that my filament detector switch is having false positives and I’m not sure if it’s a pin settings as well.

6

Most 3D printer boards have physical pull-ups on endstop pins. You would need to look at the schematic to confirm.

7

It sure does, thanks!