PCB pinout question for Servo wiring


Have you made some changes to the Firmware?
I´d like to use the “SS”-Pin for to switch an Optocoupler with it.
No changes other than setting the servo pin to 53 in pins.h.



if you want to use your free SS Connector (PIN 53) in digital than in PWM- Mode, you have to change only one line in your firmware.
go to “Marlin_main.cpp” and change in row: 1027 (for Marlin Ver.2) / row:1507 (for Marlin Ver.1) from

if (sensitive_pins[i] == pin_number)


if (sensitive_pins[i] == pin_number && sensitive_pins[i] != 53)

Now you can control your PIN53 (SS Connector on board) direct via G-Code:

M42 P53 S0 -> to LOW (0V) M42 P53 S255 -> to HIGH (+5V)
Description: PIN 53 (SS_PIN) is defined in “Sd2PinMap.h” (don’t change this setting because otherwise the controller hangs). This is required for the internal initialization for SD card mode. After initialization, the SS_PIN changes to PIN 25 as it is configured in “Pin.h”. From now PIN 53 is useless, however it is held as a important functional PIN in the “SENSITIVE PINS” list. This forbids a direct call over G-code:M42. Now, the changed code line allows the command. This only works fine if you don’t need the SS-pin on your board as the K8201 does.

From now you can use your own additional hardware to control one or more servos, for example with an Arduino Micro

greets Don



I have a BLTouch autobed leveling sensor on my K8200. I did an upgrade to the RepRap Discount Full Graphic Controller witch works fine (after some tweaking).
I connected the BLTouch same as in your photo. There are 2 additional wires that must be connected to the Z-Endstop connector.
It does a selftest so it does function.
I did try almost everything including your code to get the BLTouch to work.
My BLTouch doesn’t do anything when using any M280 command.
I used almost every firmware & marlin version. No responce of the BLTouch.
How do i know if pin 53 (ss) still works? Is there some code to test this pin?
I strugle more than a month with the BLTouch and i run out of ideas.



hello how did you make the bltouch run on the k8200 because at home it does not unfold .
tank you