Setting the precision of a quartz watch. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches

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The use of quartz resonators in electronic watches does not always provide the desired accuracy. The proposed revision will make the clock more accurate.

Adjusting the accuracy of the clock with the help of a frequency meter is extremely inconvenient, takes a lot of time and requires a fairly high qualification. Therefore, I propose a simple device that does not require the restructuring of the crystal oscillator, but only compensates for the error once a day. No tools are required, just one screwdriver is enough. In practice, the device proved to be very effective. After the first adjustment step, the error of the Elektronika-18 table clock was only 1 s per month.

The compensator (Fig. 1) is designed to operate in clocks made on K176 series microcircuits [1].

Every day at 00 hours 00 minutes, a short low-level pulse with a duration of 3 ms appears at pin 176 of the K13IE250 chip. It is used to recalculate the days of the week in calendar watches. This signal is fed to the input of a single vibrator, made on the timer DA1. The single vibrator starts up and generates a high-level pulse at the output (pin 3). Its duration is determined by the timing chain R1R2C1. Using capacitor C1 with a low leakage current, on the KR1006VI1 microcircuit, it is possible to obtain the pulse duration with high accuracy. In the proposed device, the error is no more than 0,3% over the entire range of the duration of the generated pulses from 0,45 s to 5,6 s.

The signal from the output of the single vibrator is fed to the correction input of the K176IE13 microcircuit (pin 6) and resets the minutes and seconds. The same signal also resets the K176IE12 counter (this connection is not shown in the diagram), which adjusts it to within the phase of second pulses. Depending on the pulse duration, which is determined by the position of the trimmer resistor R2, the clock correction value will also change.

Diode VD1 is used for decoupling. Capacitor C2 allows you to avoid the influence of external noise and supply voltage ripple on the accuracy of the timer [2]. The device consumes current no more than 4 mA at a supply voltage of 9 V. The supply voltage can be in the range from 5 to 16,5 V [2].

The compensator is assembled on a single-sided printed circuit board made of foil fiberglass (Fig. 2).

Fixed resistor R1 - MLT, tuning resistor R2 - SPZ-29VM. Capacitor C1 - K73-17, C2 - K10-7 or KM. VD1 - any low-power diode. The length of the connecting wires should be no more than 10...15 cm.

The printed circuit board is attached to the clock using two threaded bushings with M2,5 screws. The lid is soldered from one-sided foiled getinaks 1 mm thick. It is attached to the board with a screw through a threaded bushing.

In order for the accuracy of the course to be adjusted both positively and negatively, the quartz oscillator is tuned using a frequency meter to a frequency not of 32768 Hz, as usual, but to a frequency of 32769 Hz, so that the clock is deliberately faster by 2 ... 3 s in day. If the clock is in a hurry, then there is no need to specifically increase the frequency of the generator. The tuning is best done by measuring the period of second pulses with a resolution of 1 μs. The period value must be 999970 ±5 µs. This is a rather rough setting - it does not require a long warm-up of the frequency meter and clock, so it does not take much time.

With the middle position of the slider of the resistor R2, the indicated frequency of the crystal oscillator corresponds to the minimum error at the time of tuning. In the extreme positions of the engine, the clock is adjusted by +2,5 s or -2,5 s per day.

Using a frequency meter in the pulse duration measurement mode, the entire circumference of the resistor R2 must be divided into divisions in increments of 0,5 s per day. Thus, for example, if the clock is 10 seconds behind in 5 days, then to correct them, you need to turn the slider towards the plus (to the left according to the diagram) by one division.

The clock adjustment process is as follows. Set the R2 slider to the middle position. At a certain time, for example, at 18:00, press the button for correcting the clock according to the exact time signals. After 10 days at 18:00, record how many seconds the clock has gone. Divide this value by 5 and you will get the number of divisions by which you need to turn the slider of the resistor R2.

With a little modification, the proposed electronic unit can be used in any watch that has an alarm clock and a reset button for seconds. In this case, the start of the single vibrator will occur on an alarm signal.

Literature

1. Biryukov S. A. Electronic clock on MOS integrated circuits. - M.: Radio and communication, 1993.
2. Kolombet E. A. Timers. - M.: Radio and communication, 1983.

Author: D. Kashirskikh, Kirov

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