Control circuit for a stepping motor in battery-operated instruments

A circuit for the control of a stepping motor, comprising:

• an oscillator circuit;
• a divider circuit for producing timing signals from the output signals of said oscillator circuit;
• a drive circuit for the generation of pulses to actuate a field coil of a stepping motor;
• a measuring device for detecting current flowing through the field coil of the stepping motor and producing an output signal related thereto;
• a detection circuit for detecting the variation over time of the flow of the current through the field coil, and for terminating said actuating pulses upon detection of a predetermined change in the current;
• a delay circuit for inhibiting operation of said detection circuit for a first predetermined period of time with respect to the onset of each actuating pulse, wherein said first predetermined period of time is determined so as to insure that a derivative of the variation over time of the current under all operating conditions of the stepping motor has at least attained a minimum value, to thereby insure that the duration of said actuating pulses is not less than said first predetermined period of time;
• and
• a timing circuit for insuring that the duration of said actuating pulses does not exceed a second predetermined period of time.