I’m in the process of installing a BLTouch on a Velleman Vertex K8400. The board doesn’t have a dedicated servo pin, so I’ll assign one. No problem there.

The board only has a Z-min pin, so it’s my understanding that I’m supposed to unplug my Z-min cable and plug the BLTouch into the Z-min port.

My question is: "Can't I assign another unused pin as a Z-max, plug the BLTouch into that, adjust the firmware, and leave the existing Z-min sensor plugged in?"

Upon further review, I probably shouldn't have said Z-max, and will be more specific.

This is a Mega 2560 board with 2 available PWM pins. Anything wrong with this setup?


  #define SERVO_0_PIN 15 //PH3 (PWM)
  #define Z_MIN_PROBE_PIN 16 //PH4 (PWM)


=======Z Probe Option=======


  #define BLTOUCH

I want be able to keep my Z-min sensor plugged in as a backup to prevent a bed crash just in case the BL touch doesn't trigger. From what I see this should work as long as I make sure the BLTouch triggers before the Z-min. Any issues that anyone can see?

  • $\begingroup$ Did you install bltouch on k8400? I have the same printer and want to install auto bed leveling but I dont know how $\endgroup$
    – Ofitecno
    Jun 17, 2022 at 8:48
  • 1
    $\begingroup$ @Ofitecno - Hi and welcome to Stack Exchange. Please ask a new question - questions posted as an answer aren't permitted. Please take the tour to get a better understanding of how SE works. Thanks. $\endgroup$
    – Greenonline
    Jun 17, 2022 at 9:12

2 Answers 2


Note: The question has changed after posting this answer. This answer answered the previous question, but is now out-of-date with respect to how the question has changed; I'll update it later, as it is possible what is asked now.

You can change the Z-min and the Z-max pin assignment in Marlin Firmware in the pins_<boardname>.h file, you basically exchange the Z-min and the Z-max. Note that the switch connected to the old Z-min port now becomes a Z-max sensor if you enable that in the firmware; you should therefore remove it (the actual switch) from the minimum Z position.

To enable a BLTouch sensor you require 2 pins free on the microprocessor. One registers the signal of the trigger, the other triggers the servo to stow/deploy the sensor.

You can connect the white/black to the Z-min signal (Z-min pin) and ground of the Z-min connector (or if pins are swapped in the firmware to the Z-max). The other wires need to be connected to +5 V (red), ground (brown) and orange/yellow to a free analog pin (PWM pin):

BLTouch can be operated in the following condition.
- One I/O for control (PWM or Software PWM)
- One I/O for Zmin (Z Probe)
- GND and +5 V power

The PWM pin should be defined in your pins_<boardname>.h file, e.g.:

#define SERVO0_PIN         5 // RUMBA board


#define SERVO0_PIN         27 // ANET board

The Z-max signal pin is no PWM pin for the servo.


After studying the Marlin code, I found the answer I was looking for.

If I have a spare PWM pin, I can assign it to anything I want. So the best solution is to define the pin as a Z_MIN_PROBE and then in Configuration.h in the Bltouch settings


rather than


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