Primary clock. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches
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The system of primary clocks plus a network of secondary clocks has existed for a long time and has proven itself well in the workshops of factories, at railway stations, and in institutions. If, instead of cumbersome relays and mechanical drivers, microcircuits and transistors are used, the system can get a new life.
The author, using the modern element base, tried to create the most simple, small-sized design of the primary clock, designed for 5 - 7 secondary clocks. The device has a dual power supply, i.e. it operates from a 220 V network and automatically switches to backup power from the Krona battery in the event of a power outage. At the same time, the watch works offline for up to five days. The average current consumption from the battery is 1,5 mA. Accuracy - ±4 s per month.
The scheme of the device is shown in fig. 1. To power the device from a 220 V AC network, a mains transformer is required (not shown in the diagram), which provides a voltage of 11 V on the secondary winding. Power in this case does not play a role, the less the better, since the current consumption is very small. The alternating voltage is rectified by the VD1 diode bridge and stabilized by the DA1 chip.
(click to enlarge)
The minute pulse generator is assembled on a DD1 chip according to a typical scheme described, for example, in an article by S. Biryukov "Primary quartz watch"(" Radio ", 2000, No. 6, p. 34, 35). These pulses are fed to the input of the trigger DD2.1. From the outputs of the trigger, antiphase sequences are fed to two short pulse shapers, which are assembled on triggers DD3.1 and DD3.2. 2 (see diagrams in Fig. 2) The pulse duration is about 60 s and the period is XNUMX s.
On transistors VT2 - VT6, a voltage polarity switch is assembled. When a pulse is received from the output of the trigger DD3.1, transistors VT2 and VT5 will be opened (VT3 and VT6 are closed). When a pulse is received from the output of DD3.2, transistors VT6 and VT3 will open, and VT2 and VT5 will close. The pulse polarity at the output of the device will change to the opposite (diagram 5 - in Fig. 2). Transistor VT4 acts as a diode.
The polarity switch is powered by a micropower voltage converter, the generator of which is assembled on the elements DD4.1 - DD4.3, and the multiplier - on VD5 - VD12 and C9 - C16. The capacitance of the storage capacitor C18 indicated in the diagram (when charging it to 35 V) is enough to operate seven secondary clocks. Resistor R19 does not allow overloading the converter at the time of movement of the arrows.
The clock progress indicator is assembled on the transistor VT1. Pulses with a frequency of 1 Hz arrive at the base VT1 from the output S1 of the counter DD1. LEDs HL1 and HL2 light up alternately. In the absence of mains power, in order to save battery power, the display unit automatically turns off.
There is one feature that allows you to move the clock hands back. To do this, you need to quickly change the polarity of connecting the clock to the output of the device, so that pulses of the same polarity come to the clock in a row. Each such switching (after operation) reduces the clock reading by one minute. This is due to the peculiarity of the stepper motor.
If the number of hours connected is small, then transistors VT2 and VT6 can be KT315I, and VT3 - VT5 - KT361 I. Diodes VD2 - VD4 - germanium D9 series with any letter index.
To accurately start the clock, you need to install additional elements in the node on the DD1 chip as it was done in the article mentioned by the author
Author: V.Alferyev, Poltava, Ukraine
See other articles Section Clocks, timers, relays, load switches.
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