Clock stepper motor control circuit. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Electric motors

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In connection with the ongoing renovations and reorganization of enterprises, electromechanical clocks with centralized control are being removed from the walls of many institutions, which are becoming useless. However, such clocks can be used by mounting a stepper motor control circuit in them. The stepper motor of such watches, for example, of the "Strela" type, is started by bipolar pulses with an amplitude of about 24 V, following with an interval of 1 min. Modernization of wall electromechanical clocks is devoted to several publications [1,2].

The proposed control circuit consists of a quartz oscillator, a frequency divider, a minute pulse shaper, a phase inverter pre-amplifier, a bridge key amplifier, a short pulse shaper, and a power supply circuit. The device does not contain electromechanical relays and is placed on a small printed circuit board, which is fixed inside the watch case.

Schematic diagram of the device is shown in Fig.1.

(click to enlarge)

The crystal oscillator and frequency dividers are made on a DD1 chip of the K176IE12 type. The crystal oscillator operates at a frequency of 32768 Hz. The first stage of dividing the pulse repetition rate of the quartz oscillator contains a 15-bit binary pulse counter, from the output of which (pin 4) second pulses are fed to the second stage of division with a division factor of 60. Minute pulses from pin 10 are fed to the clock input C of the counting trigger of the DD2 microcircuit ( output 3) and through the resistor R4 to the base of the transistor VT1. The state of the upper trigger changes on the positive edge of the minute pulse.

At the trigger outputs (pins 1 and 2), we get antiphase pulses that go to the preamplifier on transistors VT2 and VT3. Amplified pulses control a bridge key amplifier on transistors VT4, VT5, VT7 and VT8. The winding of the clock stepper motor is included in the diagonal of the bridge. If the collectors of transistors VT5 and VT8 are connected to a common wire, then the circuit works, since when the transistor VT2 is closed and VT3 is open, transistors VT4 and VT8 are open, the current flows through the winding from left to right. When the state of transistors VT2 and VT3 changes, transistors VT5 and VT7 open, the current flows through the winding in the other direction. But for the operation of a stepper motor, short bipolar pulses with a duration of 0,5 s are sufficient.

To reduce the waste of electricity in the time intervals between "steps" (59,5 s), to facilitate the thermal regime, to reduce the size of the device, a short pulse shaper is introduced into the circuit - a single vibrator assembled on the lower trigger of the DD2 microcircuit, and transistors VT1 and VT6. Single vibrator [Z] is started by minute pulses from the collector of transistor VT1. A positive voltage drop occurs at the trigger output (pin 13), which, through the feedback circuit, acts on the reset input R (pin 10), returning the one-shot to its original state. The time constant of the R6C5 circuit is chosen so that the duration of the generated pulse is approximately 0,5 s. This pulse opens the transistor VT6, which allows the flow of current through the bridge amplifier.

Figure 2 shows oscillograms at characteristic points of the circuit.

Diodes VD3-VD6 protect the circuit from surges that occur on the winding of the stepper motor. Button S1 serves to reset the frequency dividers to zero and to delay the clock. Button S2 is designed to move the clock hands forward in second pulses. Trimmer capacitor C2 is used to fine-tune the frequency of the crystal oscillator. Zener diode VD2 stabilizes the supply voltage of 9 V.

The device uses resistors C2-23 and KIM (R2), capacitors K50-29 (C4 and C6), KT4-256 (C2), K10-17-16 (the rest). Quartz resonator RK-724A-17BU - from an electronic clock at a frequency of 32768 Hz. The K561TM2 chip can be replaced with K176TM2, K561TM1, K176TM1. Transistors - any silicon of appropriate conductivity and power. Any small-sized power transformer, for example, from a network adapter with a voltage of rewound secondary winding of 15-16 V.

Setting up the device comes down to checking the supply voltages with a tester, checking oscillograms. For the convenience of viewing the waveforms, it is necessary to speed up the processes in the circuit, for this, the capacitor C5 (0,33 μF) is temporarily replaced with a capacitor with a nominal value of 1000 pF, then a jumper from point 5 sends a trigger pulse from pin 1 of the DD1 microcircuit. Instead of a stepper motor, it is advisable to connect a 6 kΩ resistor to points 7 and 1 of the circuit. Oscillograms should correspond to those shown in Fig.2. After viewing the waveforms, the circuit is restored and, using a digital frequency meter connected to pin 14 of the DD1 chip (point K), in the frequency measurement mode, the frequency is set to 32768 Hz, selecting the capacitance of the capacitor C1. The tuning capacitor C2 should be in the middle position.

In some cases, it becomes necessary to increase the capacitance of capacitor C2 by soldering an additional capacitor with a capacity of 22-33 pF in parallel with it. Then the frequency meter in the pulse period measurement mode is connected to pin 4 of the DD1 microcircuit and capacitor C2 sets the repetition period of second pulses with an accuracy of 1 μs. It is advisable to carry out such an operation after the "aging" of the quartz resonator after several weeks of operation of the watch. This ensures high accuracy of the clock.

With an increase in the power of the power supply and transistors of the bridge amplifier, several secondary clocks located in different rooms of the building can be connected to this circuit. A similar device assembled on. four microcircuits [4], allows you to power up to 40 secondary clocks.

Structurally, the step-down transformer T1, the rectifier bridge VD7 and the capacitor C6 can be placed in the housing of the modified network adapter. All parts of the device, except for the buttons S1 and S2, are installed on the printed circuit board shown in Fig.3.

The dashed lines on the board show three jumpers. The printed circuit board is made of one-sided foil fiberglass 1,5 mm thick. Buttons are attached to the side wall of the watch.

References:

1. Alekseev S. Primary quartz clock//Radio. -1985. -#10. -C 44-45.
2. Giniatullin H. The evolution of electronic clocks//Radio. -1992. -#2-3. -C.18-19.
3. Single vibrators on D-triggers//Radio. - 1984. -№7. -C 58.
4. Biryukov S. Primary quartz clock//Radio. -2000. -#6. -C.34.

Author: V.V.Cherlenevsky

See other articles Section Electric motors.

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