light emitting diode serving as display element 21 in addition an output a2 of the microcomputer 17 is connected to a display element 22 and via a switch 23 to a turn off device 24 of a drive motor 25 which drives a main shaft 26 of the sewing machine through a v belt 27 an output a4 of the microcomputer 17 is connected to the reset input r of a flip flop element 28 whose setting input s is connected to an output a5 of the microcomputer 17 the output q of flip flop element 28 is connected to the input e2 of an and gate or element 29 whose input e1 is connected to the input e1 of the microcomputer 17 and whose output a is connected to the input e of a counter 30 the outputs are connected to the inputs of an and gate or element 32 the output of the and gate or element 32 is connected to the input e2 of the microcomputer 17 and via a diode 33 to the reset input r of counter 30 as well as to the reset input r of the flip flop element 28 during operation of the sewing machine light beam 12 is radiated from the light emitting diode 13 onto the opening 10 in the bobbin capsule 3 as soon as the shuttle thread 5 on bobbin 6 has diminished to the extent that beam 12.