BL Touch – Reset Operation Mode

Operation Modes

The BL Touch has 2 operations modes. The default is the “open drain” mode and this is what the probes ship with. The other is the 5V mode. The default mode for all TH3D firmware is the “open drain” mode and that is what our firmware is setup to use. If you are having odd results you can force a mode reset on you BL touch to force it into the open drain mode.

Resetting the Operation Mode

All that is needed on our Unified 2 firmware to reset the operation mode to the “open drain” one is to add one line to your configuration.h file. Once you have this added, compile the firmware, and update your printer board.


When the BLTOUCH_FORCE_MODE_SET is enabled it will set the BL Touch mode to its EEPROM (the probe EEPROM, not the printer board) to the “open drain” mode. This happens on every startup or reset of the printer board. When the mode set happens, the pin will deploy and the red led will flash 3 times quickly. The pin will pull back up and the red light will come back on solid.

It is recommended (by Marlin) to then remove that line you added in the above step and re-upload to the printer board so you do not wear out your BL Touch sensor memory.

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