Woodworking hand planer safety device detection circuit

The circuit of the woodworking hand planer safety device is divided into two parts: the detection circuit composed of quartz crystal, etc.,
and the main circuit and control circuit of the planer motor, which consists of the quartz crystal HTD and the transistor VTi inter-electrode capacitance
to form an oscillation element, with an oscillation frequency of 3MHz. When the hand approaches the danger zone of the tool axis, the oscillation frequency suddenly changes, the output signal of the transistor
VTi suddenly decreases, VT2, VTa, and VT4 are cut off, the relay KAI is released, causing the contactor KMi
to be released, and the motor brakes quickly. After parking, press the start button SBi again, and the planer will resume normal
operation.
    The inductor L is made of 0.15mm diameter sheathed wire wound on a high-frequency magnet with 133 turns.