Circuit for an Electronic Clock Having a Parallel-Connected Alarm Device and Stepper Motor

The invention relates to a circuit arrangement for an electronic clock with an alarm device, comprising a stepper motor, driven by a quartz oscillator with an associated frequency divider, which stepper motor drives the display elements, and comprising a PXE (piezoelectric oxide) element which generates the alarm signal.

Such circuit arrangements are generally known. FIG. 1 shows an example of one such prior art circuit. An electronic circuit 1, which is not shown in more detail, generally an integrated circuit (IC), in conjunction with a quartz resonator 2 and a voltage source 3, generates a constant frequency, which after multiple division supplies a second-pulse to a stepper motor 4, which moves the display elements, not shown, for example the hands. A switch 5, which is mechanically coupled to the hour-hand, actuates an alarm device at a preset time, which device in the present example comprises an inductance 6, a PXE (piezoelectric oxide) element 7, and a transistor 8. When the switch 5 is closed at the preset alarm time, a frequency of 4.194 kHz, derived from the frequency divider, is applied to the base of the transistor 8, so that the PXE (piezoelectric oxide) element 7 (electromechanical piezoelectric oxide transducer) generates audible vibrations, the inductance 6 constituting the d.c. path for the transistor 8.

The control pulses for the stepper motor 4 may, for example, have a duration of 1/32 sec., as is indicated in FIG. 1 at the bottom right.

It is an object of the present invention to simplify a circuit arrangement of this type in such a way that the inductance 6 and the transistor 8 may be dispensed with. According to the invention this is achieved by connecting the PXE element in parallel with the winding of the stepper motor and by providing the frequency divider with a switch, which upon closure in the interval between every two stepping pulses supplies the frequency required for driving the PXE element in the parallel arrangement of the motor winding and the PXE element.

It is apparent that the resonant frequency of the PXE element 7 and the derived frequency of 4.194 kHz should correspond in order to obtain optimum efficiency.

It has been found that the d.c. pulse of 1/32 sec. duration required for controlling the motor 4 does not influence the PXE element 7, while on the other hand the stepper motor 4 is not influenced by the high frequency.

FIG. 1 shows a schematic and waveform diagram of a prior-art circuit for an electronic clock; and

FIG. 2 shows a schematic and waveform diagram of a circuit for an electronic clock in accordance with the invention.

FIG. 2 shows an embodiment of a circuit arrangement in accordance with the invention. This embodiment again comprises an integrated circuit 1, a quartz resonator 2, a voltage source 3, a motor 4 and a contact 5. As can be seen, the PXE (piezoelectric oxide) element 7 is connected in parallel with the winding of the stepper motor 4. The integrated circuit 1 includes a switch 9, which--after closure of the contact 5--in the interval between every two control pulses for the stepper motor supplies a voltage having a frequency of 4.194 kHz to the parallel connection of the stepper motor 4 and the PXE element 7. The corresponding pulse diagram is shown in FIG. 2 at the bottom right.

When the circuit proposed by the invention is used, inductance 6 and transistor 8, as used in FIG. 1, may be dispensed with, for a considerable saving in size and cost.