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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Hours on LED indicators KLTs202A. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches Table clocks, which this article talks about, differ from many similar designs in that they do not use luminescent, but large-sized LED indicators. The alarm clock in this watch emits a two-tone signal with an adjustable sound time and has an on indicator. In addition, the design provides blanking of an insignificant zero on the clock display and redundant power supply for clock microcircuits. Schematic diagram of the clock is shown in fig. 1. They use four large-sized LED indicators with a common anode to display the time. In the experiments, KLTs202A, KLTs202V, KLTs402B with h = 18 mm and KIPTs04A with h = 25 mm were used. The watch itself is based on the K176IE12 and K176IE13 integrated circuits described in [1, 2]. Elements DD1, ZQ1, R1, R2, C1 - C3 form a generator with a frequency divider, and DD2, VD3 - VD5, R5, C4 - the main counter with controls. The inclusion of these microcircuits is typical. As a cathode decoder, a K514ID2 TTL chip was used, powered by the +Upit circuit through a ballast resistor R9. Such an inclusion is somewhat incorrect, since the input voltages for K514ID2 exceed the permissible ones in this case. But this also has its advantage - it was possible to remove cathode switches from the clock (seven transistors with basic resistors).
Anode keys are made on transistors VT3 - VT10. The device for suppressing an insignificant zero is simplified as much as possible and contains only three elements - VD7, VD8, R17. Its action is based on fixing the ignition of segment f, which is a hallmark of the number 0 in relation to the numbers 1 and 2. When a low logic level (less than 1 V) appears at the output f of the decoder, the VD8 diode opens and shunts the base current of the transistor VT9. Key transistors VT9. VT10 closes and turns off the tens of hours indicator. As dividing points of the dial, single LEDs HL1 and HL2 are used, flashing to the beat of second pulses. The indication shutdown unit contains a thyristor VS1 and a transistor VT2. In operating mode, VS1 is held open by the supply current of the DD3 microcircuit passing through it, the value of which is in the range of 30 ... 40 mA. When the mains power is turned off, VS1 closes, the DD3 chip is turned off from the power supply and the indicators go out. When the power is turned on, the thyristor VS1 remains closed and the numbers do not light up, although the dividing points flash. This attracts the user's attention and reminds him that after turning on the watch, their readings must be checked against other watches (after all, it is not known how long the power outage was). The indication is turned on by pressing the button SB3 ("B"), while the pulses with a frequency of 128 Hz, which appeared on the basis of the transistor VT2, are amplified by the current and open the thyristor VS1. The alarm clock is made on DD4 and DD5 chips and works as follows. Pulses from the HS output of the K176IE13 chip are detected by the VD9R18C6 circuit, and a negative voltage drop from the output of the DD5.1 element through the R19C7 circuit starts the waiting multivibrator on the DD4.4 and DD5.2 elements. As a result, the generator on the elements DD5.3, DD5.4 is turned on and its antiphase output signals control the operation of the switch on the elements DD4.1 - DD4.3. As a result, either a frequency signal of 512 Hz (from pin 1 of the DD4 microcircuit) or 1024 Hz (from pin 5 of the DD4 microcircuit) passes to the base of the output transistor. Thus, a two-tone signal is formed, interrupted by pulses with a frequency of 1 Hz, coming through the resistor R24. The switching frequency of the switch is determined by the parameters of the elements R23, C9, and the sounding time of the signal - by the elements R21, C8. With the ratings of the elements indicated on the diagram, this duration can be changed from 0 to 60 s. The SB5 button acts as an alarm switch, and the HL3 LED is an indicator of its on state. Diode VD10 blocks the output of a sound signal in case of false operation of the waiting multivibrator at the wrong time (for example, due to interference). The clock power supply consists of a transformer T1, a rectifier - VD13C10, and a voltage regulator on the elements VT12, VD14, R28 (Fig. 2). Its output voltage is about 8,5 V. In the event of a mains power failure, the DD1, DD2 microcircuits are powered by capacitor C5, due to which the clock is maintained for some time (of course, without time indication). A number of clock elements in this mode eliminate leakage from the outputs of operating microcircuits to the disconnected part of the clock device.
So, the VD12 diode prevents current leakage through the pin. 5 DD4 chips. The emitter junction of the transistor VT1 is closed by the diode VD1, and the outputs of the K176IE13 chip are transferred to a high-resistance state by a low logic level at the input V. The high resistance resistor R24 reduces the leakage through the pin. 8 and 12 DD5 chips. All these measures make it possible to efficiently use the energy of the charged capacitor C5. The capacity of the latter is chosen based on the expected duration of power outages. Experimentally, at Upit = 9 V, the following values of the stroke retention time were obtained for the following capacitances of the capacitor C5:
With longer power outages, the use of a conventional capacitor becomes irrational; better results can be obtained when using an ionistor or a battery. A capacitor with a capacity of 1 F x 6,3 V supports a stroke of no more than 20 hours (the switching circuit of C5 in this case must be changed in accordance with Fig. 3), and a battery of four cells D - 0,26 D - more than four days. In the latter version, it is useful to supplement the watch with an automatic battery charger.
Of course, all the above methods of power supply do not exclude the classic solution - the use of the Krona battery or the like. The main components of the clock are assembled on a printed circuit board measuring 120x70 mm. During installation, fixed resistors were used: KIM (R1) (it can be replaced by 2 - 3 MLT resistors) and MLT (the rest), a variable resistor - SDR - 9a (R21). All oxide capacitors - K50 - 16, K50 - 33 or imported analogues, C1 - KT4 - 25, the rest - ceramic K10 - 7 or KM. Capacitors C11 - C13 are soldered directly to the power leads of the microcircuits DD1, DD2, DD4. As a transistor VT12, you can use KT815, KT817; and transistors VT4, VT6, VT8, VT10 - KT208, KT209, KT313; the rest - KT315, KT3102, KT503 with any letter indices. A heat sink is fixed on the VT12 transistor in the form of an aluminum plate 15x25 mm in size. Zener diode VD14 - any small-sized one, with a stabilization voltage of 9 ... 10 V at a stabilization current of at least 20 mA (D814B1, D814V1, D818 (A - E, etc.). Diodes VD1 - VD12 - any small-sized silicon. The thyristor is suitable from the KU101 series. HL1 and HL2 LEDs are chosen in the same color with digital indicators (and preferably of the same shade) HL3 LED with a glow of any color A quartz resonator is used in a cylindrical case from a watch Dynamic head - any power of 0,5 or 0,25 W with sound impedance coils 50 Ohm.It is also possible to use telephone capsules TA - 4 (65 Ohm) and TK - NT - 67. Switches SB1 - SB5 - P2K, they are all mounted on a common bar, and the buttons SB1 - SB4 without fixing, and SB5 with a return TP1 - 8 with a quenching resistor in the secondary winding circuit (MLT - 8 with a resistance of 1 ohms) was used as a transformer T24. In general, any small-sized transformer with a secondary winding voltage of 10,5 ... 11,5 V at a load current of 200 ...250 mA (exceeding this voltage is undesirable due to the deterioration of the thermal regime in the watch case). In place of the DD4 and DD5 microcircuits, similar ones from the K561 series can work. Decoder DD3 - K514ID2 in a case with a plenary pin arrangement. It can be replaced by a more affordable KR514ID2 chip in a plastic case. On the circuit diagram (see Fig. 1), the numbering of all pins for this microcircuit is indicated in brackets. The clock is set in the following sequence. First, the clock must be connected to the network and make sure that when you press the SB3 ("B") button, the indication turns on steadily. If this does not happen, it is necessary to select a thyristor or replace the VT12 transistor with another one with a high gain. After that, by selecting the resistor R4, you need to set the desired brightness of the flashing dividing points (HL1 and HL2). Then you should set the alarm. To do this, turn off the diodes VD10 and VD11 and check the operation of the waiting multivibrator by applying a logic zero level to the pin. 12 DD4 chips. At the same time, on the output 4 microcircuits DD5 should form a negative pulse with a duration depending on the position of the resistor R21 slider. Next, by selecting elements R23 and C9, you need to set the switching frequency of the switch (within 6 ... 12 Hz) according to the most pleasant sound of the alarm clock, and by selecting resistor R27 - the brightness of the HL3 indicator. After that, the diodes VD10 and VD11 should be returned to their place. If it is not necessary to change the duration of the alarm signal, the variable resistor R21 can be replaced with the corresponding constant. At the next stage, the quartz oscillator is tuned using an electronic counting frequency meter (both the clock and the frequency meter must be warmed up for 1 hour before measurement). First, the rotor of the capacitor C1 must be placed in the middle position and, by selecting capacitors C2 and C3, set the generation frequency close to 32768 Hz, controlling it on the pin. 14 DD1 chips. Then, by rotating the rotor C1, the exact frequency value of 32768,0 Hz is achieved. More precise tuning is possible when measuring the oscillation period on the pin. 4 microcircuits DD1 (1 s) with a resolution of 0,1 μs. In conclusion, by selecting a resistor R9 should be set to pin. 16 microcircuits DD3 voltage in the range of 4,75 ... 5,25 V (of course, with the indication on). And now a few words about the possible refinement of the watch. In the described design, four types of indicators were used, as already noted, but only KLTs202V devices can provide a really good glow. Alas, the trouble with many domestic indicators, especially large ones, is the large unevenness of the glow both within the segment and between adjacent segments, as well as a significant spread in brightness even at operating currents close to maximum. One of the solutions to this problem is the use of foreign indicators with a common anode (single or double), as well as special four-digit clock assemblies. It is fundamentally important for this circuit to have a separate anode output from each discharge, and for four-digit assemblies, it is also possible to display time in a 24-hour format. Another example of clock refinement is the introduction of an electronic alarm switch (Fig. 4). At the same time, a latching switch is removed from the old design, as a result of which all control can be carried out with small-sized buttons (PKN - 150 - 1 or the like). The alarm clock is turned on by any of the buttons SB1 - SB3 ("B", "H", "M"), and turned off by a separate button SB1 '("C"), installed instead of SB5. After a power outage, the alarm is forced to turn on. (In Fig. 4, the newly introduced elements are numbered with a prime.)
It should be noted one drawback inherent in such watches - reduced contrast with strong external illumination. For this reason, it is desirable to place the clock in a darkened part of the room, avoiding direct sunlight on it. It is desirable to eliminate the incorrect matching of the outputs of the DD2 chip with the inputs of DD3. To do this, five emitter followers should be installed between the microcircuits on any low-power silicon pnp transistors, for example, KT361. The bases of the transistors must be connected to the outputs of DD2, the emitters to the corresponding inputs of DD3, the collectors to the common wire. Literature
Author: D. Nikishin, Kaluga
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