Introduction - If you have any usage issues, please Google them yourself
When there is no magnetic material near the magnetic testing sensor, the magnetic testing sensor, open Q1 conduction.
When magnetic material near the magnetic testing sensor, magnetic detection sensor conduction, in the base of Q1 get make Q1 turn-on voltage, namely the Q1 conduction, the power the R6- D3- Q1- to form the current loop, the D3, P1.0 for low level at the same time.