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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Automatic timer for TV. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches Modern TVs can automatically turn off after a certain, user-defined time or at the end of TV programs ("SLEEP" function). A homemade timer that provides such an opportunity is discussed in the article published here. It can be used in older TVs. Currently produced imported TVs are equipped with a wide variety of user functions. One, and very convenient, function can be considered the SLEEP ("sleep") mode, which allows the user to choose the time interval after which the TV switches to standby mode. It is also worth noting such a function as the AUTO SLEEP mode, in which the device turns off when the channel ends. In our country, a large fleet of early release TVs is operated, in which many service functions are missing. The device proposed for repetition by radio amateurs is designed to equip the old device with the SLEEP mode. When using it, there is no need to select the time interval for turning off the TV, it also turns off at the end of TV shows. The device consists of two complementary parts: analog and digital. The analog part extracts unchanging horizontal synchronization pulses from the full color television signal (PCTV), while the digital part provides the timing and the necessary operation logic. The use of digital microcircuits of the K561 series in the device simplified its establishment, and an additional power source was not required, due to the high efficiency of the microcircuits. Schematic diagram of the timer is shown in fig. 1. It contains a delay node (elements DD1.3, R1. C1, VD1), which does not allow the timer to work during transients that occur on the TV after it is turned on, and resets the counter DD2. performing the functions of the main time meter. In addition, it includes a master oscillator (DD 1.1, DDI.2. R3. C2), generator 34 (DD5.1. DD5.2, R5, C3) and a pause pulse counter DD3.
The cascade on the transistor VT3 selects and pre-forms sync pulses from the PCTV, which have constant amplitude and frequency. The cascades on transistors VT4 and VT5 amplify them, the diodes VD7, VD8 are rectified, and a constant component is allocated on the capacitor C11. Element DD4.2 plays the role of a threshold element. At the moment the TV is turned on, the capacitor C1 of a relatively large capacity is discharged and level 1.3 is present at the output of the DD1 element, which prohibits the operation of the counter DD2. All its outputs are in the state 0. The generator 34 on the elements DD5.1 and DD5.2 also does not work. Transistor VT1 is closed. Level 1 at the output of element DD4.1 sets counter DD3 to state 0. Key VT2 is closed. From the PCTV passing through the isolation capacitor C5, the integrating (R12C6R13) and noise suppressing (R14C7VD6) circuits emit clock pulses, which are amplified by the transistor VT3. Then, from its collector load (R15, R16), the pulses pass through the R17C8 circuit to the emitter follower on the VT4 transistor. Further, through the capacitor C9, they come to the base of the transistor VT5, operating in key mode. Diodes VD7, VD8 with capacitor C11 form a clock rectifier. In their absence, the capacitor C11 will have a very low voltage due to interference. The comparator that distinguishes the useful signal is the DD4.2 inverter, which operates when the voltage at the inputs is higher than Un„, / 2. Resistors R22 and R23 form a discharge circuit of the capacitor C11 and at the same time a divider that determines the operation of the inverter DD4.2. When receiving PCTV at the output of the element DD4.2, level 0 appears, which acts through the diode VD9 on the input of the element DD4.1, is inverted and disables the counter DD3. After charging the capacitor C1 counter DD2 counts the set time interval. Upon reaching it, counter DD3 will start working. which determines the turn-off delay time, and the generator on the elements DD5.1. DD5.2. R5, C3, warning sound or light signal about the end of the countdown. Switching to any other channel after charging the capacitor C1 will return the device to its original state. Loss of sync pulses causes the DD4.2 comparator to switch to state 1. Turns off the speaker system and enables the DD3 counter (without light or sound warning). The TV will turn off after the set time interval. The user is warned and the TV is turned off regardless of the signal coming from the radio channel or the external video signal. Establishing a timer basically boils down to choosing the desired time interval, ie, one of the outputs of the counter DD2. and pauses (ie, one of the outputs of the counter DD3). Due to the fact that the counter DD2 doubles the pulse repetition interval in steps, intermediate values can be obtained by adjusting the frequency of the master oscillator (the values of the elements C2 and R3). With the specified parameters, the main countdown lasts about 1 hour 20 minutes, the pause time is 30 s. And there is no need to achieve high accuracy. The main countdown is from the last program changeover. When checking the operation of the monitoring device, it is convenient to use the chains assembled according to the scheme in Fig. 2. The first of them, observing the polarity, is connected between point 3 and the common wire (it is also useful to connect any loudspeaker with a resistance of 4 to 20 ohms in parallel). The second one is connected to the collector of the transistor VT2 and the positive conductor of the power source. The third chain is connected between point 5 and the positive conductor of the power source.
When the timer is powered on, the third sound blocking LED lights up (transistor VT6 is open). and after 15 seconds, the second off-mode LED turns on (transistor VT2 opens). When is the PCTV. both LEDs go out. To speed up this process, the capacitance of the capacitor C2 is temporarily reduced by a factor of three. In order to simulate the user's command, the output of the anode of the VD3 diode is briefly connected to the positive conductor of the power source. In this case, the first LED lights up first and an intermittent sound signal sounds (transistor VT1 turns on). after 30 seconds, the second LED lights up (off mode when the transistor VT2 is opened). When changing the countdown time and selecting another counter output DD3, the CP input (pin 13) must also be connected to this output. Level 1 on it ensures that the timing stops. In the event of a fuzzy operation of the DD4.2 element, a voltage boost should be applied to the anode of the VD7 diode, disconnecting it from the common wire and connecting it to the engine of a tuning resistor with a resistance of 47 ... 100 kOhm. The other two terminals of the resistor are connected to a power source. By adjusting the resistor, they provide a clear operation of the DD4.2 element. The device is designed for connection to 3USCT TVs and subsequent modifications that contain color blocks MTs402, MTs403, MTs501, etc., equipped with a remote control system on a KR1506HL2 chip, a KUTs-1 relay and a button to turn off the TV. If there is no CDS, then an additional button should be inserted into the TV to turn it off without fixing (P2K or PKN), the power switch should be replaced with a button without fixing to turn on the device, and the shutdown assembly by a timer signal should be assembled according to the diagram in Fig. 3 (numbering of elements corresponds to Fig. 1). When installing the unit in the TV, be sure to remove the plug from the socket and make sure that the connections are correct.
On the TV, +12 V is applied to the timer. Point 1 of the timer is connected to pin 7 of connector X1 (A1). to which the video signal or PCTV comes, and point 2 - to pin 1 of the K1106HP2 microcircuit or pin 4 of the K04KP020 microassembly. Connection to the output of the microcircuit is provided in order to exclude dependence on the position of the APCG switch, otherwise the signal will need to be inverted. Point 3 is connected to pin 11 of the MDA3505 (K174XAZZ) chip or leave a chain with an LED by installing it on the front panel of the TV. In this case, horizontal stripes will be observed. You should visually verify the presence of a 75 ohm resistor between pin 11 of the microcircuit and the common wire. Point 4 is connected to pin 12 of the KR1506KhL2 microcircuit, and point 5 to pin 2 of connector X1 (A1) or pin 8 of the UPCZ-2 microassembly. In the device, in addition to those indicated in the diagram, you can use K561LA7, K561LE5, K561LN1, K561IE10, K561IE9 microcircuits and other transistors of the KT209, KT315 series with any letter index, KD521, KD503 diodes. KD509, D18, D9 also with any index, resistors VS or MLT, capacitors K73-17. KM. KD. K50-6, K50-12. In the case of using elements of the K176LP11 microcircuits (indicated in the diagram) or K561LE5, the diodes VD5, VD9 and the resistor R6 can be excluded, and the signals from the DD2 counter and the DD4.2 element can be applied to separate inputs of the DD4.1 element. Author: N. Latchenkov, Moscow
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