Stepping motor control circuit capable of detecting external magnetic field

The invention relates to a control circuit of a stepping motor. The motor comprises a bipolar permanent magnet, a stator for limiting two isthmus parts and two rest positions of a rotor, and a coil mounted on a stator magnetic circuit. The control circuit comprises means for determining the rest position of the rotor, an electric pulse generator and a circuit for detecting an external magnetic field, the circuit being formed by:-a circuit for measuring the current in the coil after the electric pulse has been triggered,-a circuit for comparing the measured current with a reference current, -a circuit for measuring the rise time between the triggering of the electrical pulse and the next time at which the current flowing in the coil reaches the reference current, and-a circuit for processing the rise time, which is arranged to be able to determine whether the measured rise time indicates the presence of a given external magnetic field, the external magnetic field passes through the two isthmus portions accordi