I opened a 3D Touch bed probe to see how a small retractable contact sensor works. This unit is a BLTouch style clone. The photographs document the clone itself, while the genuine BLTouch documentation is a useful reference for the operating idea.
Inside the probe
The main parts are a plastic push pin, a small coil, a magnetic moving part and a controller board. The coil changes the position of the pin. The electronics read the pin state and provide a separate trigger output to the printer controller.
This arrangement is different from an inductive probe. It touches the bed, so it can work with glass and other nonconductive surfaces. It also avoids a normal exposed microswitch. The probe still depends on a straight, clean pin and a rigid mount.
Signals and power
A BLTouch type system normally has two interfaces. A servo style control signal commands the pin, and a second output reports the probe event. The genuine BLTouch uses a Hall sensor and a solenoid. ANTCLABS specifies less than 15 mA in standby and a short pulse below 300 mA while the pin moves. Those values belong to the genuine device and should not be used as guaranteed ratings for a clone.
Wire colors are not a reliable pinout across clone versions. Check the exact board documentation and verify ground, 5 V, control and trigger with a meter before connection. A reversed supply can damage both the probe and the printer board.
Practical checks
- Mount the body square to the bed and keep the pin vertical.
- Move the pin by hand only when power is off.
- Run the printer firmware self test before homing the Z axis.
- Keep one hand near the power switch during the first homing test.
- Repeat the probe test at one point and compare the spread before trusting a full mesh.
The ANTCLABS BLTouch technical page explains the genuine sensor, its signal timing and its current requirements.
Project photographs
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