the n 1 n 2 correspondingly in step s 70 when the metal detecting apparatus 10 detects one of the metal blocks 410 again the output pin p 101 of the metal detecting apparatus 10 outputs a low level signal such as u201c 0 u201d to the input pin p 11 of the scm 12 the scm 12 adds one to n 1 stored in the storage module 5 in step s 80 when the photoelectric device 2 detects one of the holes 412 again the output pin p 21 of the photoelectric device 2 outputs a low level signal such as u201c 0 u201d to the input pin p 12 of the scm 12 the scm 12 adds one to n 2 stored in the storage module 5 in step s 90 the scm 12 outputs n 1 and n 2 to the display module 3 via the output pin p 19 the display module 3 displays n 1 n 2 correspondingly in step s 100 the scm 12 determines if n 2 is equal to the predetermined number of testing cycles of the motor 42 stored in the storage module 5 if yes the procedure goes to step s 110 if not the procedure goes back to step s 70 in step s 110 the output pin p 17 of the scm 12 outputs a low level signal such as u201c 0 u201d to stop the motor 42 the display module 3 displays n 1 and n 2 in the.