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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Proportional telecontrol system. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio control equipment Our magazine has repeatedly talked about discrete telecontrol equipment. It is reliable in operation, its encoder and decoder are easy to manufacture and set up, but the discrete system has one significant drawback - it does not allow the implementation of complex control algorithms. Greater flexibility can be provided by the so-called proportional system. In this article, we introduce readers to one of its options. As usual, only the encoder and decoder are described. The encoder uses the most common now pulse-width coding method with time division multiplexing. The average duration of information pulses (ti = 2 ms) and pauses between them (tp = 0,3 ms) is not much different from that. which is accepted in industrial equipment. However, for smoother control of electric motors, the increment in the duration of the information pulse (dt) in the extreme position of the control knobs is ±1 ms, which is more than generally accepted. To simplify the control of electric motors, the period T of the repetition of information packets is chosen constant and equal to 16 ms. At the end of each information packet, a pause is formed, which is necessary for synchronization of the receiver distributor. When moving the control knobs, the duration of the synchropause (tsp) varies from 3 to 11 ms. Schematic diagram of the encoder is shown in Fig.1. and signals at some of its points - in Fig.2. The bottom diagram in Fig. 2 shows the information package for one command transmission cycle in a four-channel equipment.
The main node of the encoder is a generator of rectangular pulses. It consists of a source follower on the transistor VT3 and a Schmitt trigger on the elements DD4.3, DD4.4. The generator also includes resistors R11 -R14 and a decoder DD2.
When the power is turned on, a low level signal is set at the output of the DD4.4 element. Capacitor C2 will be charged through an open transistor VT2, and capacitor C4 will be charged by the flowing input current of element DD4.3 through resistor R9. Since the charging time constant of capacitor C2 is less than that of C4, then by the time the Schmitt trigger switches to a single state, capacitor C2 will be charged to a voltage of about 5 V. The charging time of capacitor C4 determines the pause between information pulses. After switching the element DD4.4 to a single state, the transistor VT2 closes and the capacitor C2 begins to discharge one of the resistors of the remote control selected by the decoder DD2. The voltage from the capacitor C2 through the source follower VT3 and the diode VD1 is supplied to the Schmitt trigger. When this voltage decreases to the switching threshold, determined by the position of the trimmer resistor R7, the trigger switches to the zero state - an information pulse is formed. The state of the decoder DD2 is determined by the signals coming from the counter on the triggers DD1.1 and DD1.2. The counter switches at the time of the decline of each information pulse and alternately connects resistors R11--R14 to the generator. When on the inverted outputs of triggers DD1.1. DD1.2 will be signal 1, then a low-level signal will appear at the output of element DD3, prohibiting the operation of the Schmitt trigger. In this time interval, a synchropause is formed. Again, the generator will be started by a pulse from a clock generator assembled on a transistor VT1 and elements DD4.1 and DD4.2. The encoder is fed from a voltage regulator made on transistors VT4, VT5 and a zener diode VD2. The use of this stabilizer made it possible to increase the stability of the entire device. The encoder is operational when the voltage changes from 7 to 15 V. The current consumed by the device is 10 ... 11 mA. Instead of the bipolar transistors indicated in the diagram, any silicon low-power transistors of the appropriate structure can be used. Transistor KP303G can be replaced by KP303D, KP303E. Instead of KP303A, you can use any transistor from this series with a cut-off voltage of not more than 1,5 V. Diode VD1 - any germanium. The K134LA2 chip can be replaced with a chip from the K106 or K136 series. Replacing the rest of the chips is undesirable, as this will lead to the need to recalculate the encoder. Capacitors C1 and C2 must be paper, metal-paper or film, since the stability of the encoder depends on them: C3 - K50-3. Thermistor MMT-1 (RK1) can be replaced with KMT-12, MMT-9. Resistors R11-R14 - SP-1. Their resistance can be from 68 to 150 kOhm, but if the angles of full rotation of all control knobs are chosen equal, then the values of all resistors should be the same. The inputs of the DD3 chip not shown in the diagram (pins 3, 5, 8, 9, Fig. 1) must be connected to any of the connected inputs. Before setting up the encoder, it is necessary to set the initial resistance (Rini) of the console resistors. This resistance is determined by the formula:
where R is the nominal resistance of the remote control resistor, a is the full angle of rotation of the engine, da is the angle of rotation of the engine when the control knob is moved from neutral to one of the extreme positions. For a resistor SP-1 (a=255°) with a resistance of 100 kOhm at da equal to 45°, the initial resistance should be 35 kOhm. Resistor R3 is selected so that the clock cycle is 16 ms. If the duration of the negative clock pulse differs from 4±0.5 ms. it is necessary to set it within the specified limits by selecting a resistor R2. After that, an oscilloscope is connected to the output of the encoder and, by rotating the tuning resistor R7, the generation of information packets is achieved. Resistor R7 is set to a position where the duration of each information pulse with the neutral position of the control knobs is 2 ms. Radio control equipment must work stably over a wide temperature range, so the correct choice of resistor R8 is an important final step in establishing an encoder. First, instead of resistors Rl 1-R14, fixed resistors equal to Rini are connected to the encoder. Then the encoder board, together with an exemplary thermometer, is wrapped with several layers of fabric (for thermal insulation) so that the power and output conductors are free, and placed in the freezer of the refrigerator for an hour. After that, the board is removed and, without unfolding, is connected to a power source and an oscilloscope. When the thermometer shows 5 ... 10 ° C, the duration of any information pulse is measured. Then, without unfolding the board, it is slowly heated (for example, wrapped in a heating pad). At a temperature of 45 ... 50 "C, the duration of the same pulse is measured again. If the difference in duration between the cold and heated encoder exceeds 0,1 ms, then the resistance of the resistor R8 must be increased by approximately 100 ohms for every 0,1 ms difference. If the pulse of the heated board will be shorter, then the resistance of the resistor must be reduced in the same ratio. In the receiver, the signal from the output of the detector is fed to the input of the distributor, which divides the information packet into four separate channel pulses, which are fed to their decoders. Schematic diagram of the distributor is shown in fig. 3. Reinforced by the DD1.1 element and brought to the TTL levels by the DD1.2 element, the information packet enters the selector that selects the sync pauses (DD1.4. VD1, C1) and through the inverter DD1.3 to the input of the counter (DD2.1, 1) 02.2). and further to the decoder-demultiplexer DD3, DD4. Since the information pulses received by the receiver have a level of 0, then the output of the DD1.4 element will be level 1. The same level will remain in the pause between the pulses because the pause is not long enough to charge the capacitor C1 to a high level and change the state of the DD1.4 element .four. The counter DD2.1, DD2.2 changes its state on the decline of each information pulse, allowing them to alternately pass to each output of the decoder-demultiplexer.
After 1 ms after the start of the synchropause, the capacitor C1 is charged to the switching voltage of the element DD1.4. A low level is set at its output, and triggers DD2.1, DD2.2 switch to state 0, which corresponds to the selection of the first channel. When the next information packet arrives, the DD1.4 element switches to a single state, and the pulse distribution process will be repeated. The adjusting distributor does not require any and starts working immediately. Only when connecting it to the receiver may need to select the resistor R1. It is selected, achieving stable operation of the distributor with the greatest change in the amplitude of the signals from the receiver. Negative information pulses from the distributor outputs are fed to four identical channel decoders. On fig. 4 shows a diagram of one of them, and the signals at its characteristic points are shown in fig. 5.
Negative pulse-width modulated information pulse, passing through the repeater DD1.1, DD1.2 and the differentiating circuit C1R2, starts a single vibrator (VT1, DD1.3, VD1), which generates a negative exemplary pulse, the duration of which is determined by the formula:
where Ucontrol - voltage at the input control. decoder. Negative information and positive exemplary pulses are fed to the coincidence node DD2.1, DD2.2. On the same node, only on the elements DD3.1, DD3.2, receive positive information and negative exemplary pulses. If the information pulse is longer than the exemplary one. then a differential positive pulse will appear at the output of the moment DD3.2, and if vice versa - at the output of the element DD2.2 (see Fig. 5, the signal at the output of the elements DD3.2 and DD2.2). The difference pulses of the coincidence nodes come to two identical pulse lengthening devices. The first consists of an integrator (C3, R5, VD4, R4), an emitter follower (VT2) and a Schmitt trigger (DD2.3. DD2.4), and the second consists of an integrator (C4, R11, VD6, R10), an emitter follower ( VT3) and Schmitt trigger (DD3.3, DD3.4). Since the time constant for charging capacitors C3. C4 is much less than the discharge time, then positive pulses will be formed at the output of the Schmitt triggers, the duration of which is proportional to the duration of the difference pulses. The duration of the positive pulses will be 16...40 times longer than the duration of the difference pulses. The voltage stabilizer (VT1, VT2, VB2, C2) is designed to power the distributor and all decoders (see Fig. 3). The distributor and each of the decoders consume a current of no more than 6 mA. The decoder transistors and the voltage regulator transistor VT1 can be any silicon. The KP303G transistor in the stabilizer can be replaced with KP303D. KP303E, and K134LB2 microcircuits in the distributor - on K106LB2. To establish a decoder, a generator is required that generates pulses with a duration of 1 ... 3 ms and a repetition period of 16 ms. If there is no such generator, then you can use an encoder by connecting a distributor to it. The signal from the encoder is fed to the input of the distributor element DD1.2, and output 1 of the DD1.1 element is temporarily disabled. The decoder single vibrator is tuned at the voltage at the control input. 2,2 V. Negative pulses are applied to the signal input, and the resistor R3 is selected so that the duration of the negative pulse at the output of element DD1.3 is 2 ms. If the decoder is designed to turn on the motor for a certain time, then jumpers are installed instead of resistors R5, R11. Pulses with a duration of 2,3 ms are applied to the decoder (a difference pulse with a duration of 3.2 ms will appear at the output of the DD0,3 element) and resistor R10 is selected so that the duration of the pulses at the output of the DD3.4 element is 12 ... 15 ms. Then, the duration of the input pulses is reduced to 1,7 ms (difference pulse 0,3 ns) and the resistor R4 is selected so that the output of the DD2.4 element has pulses with a duration of 12 ... 15 ms. If the decoder is used to control the speed of the motor. then on the Input ex. a voltage of 2,2 V must also be applied, and the duration of the output pulses must be 2,8 ms. Resistor R11 is selected so that capacitor C4 is charged to a voltage of 2,5 V. Resistor R10 is selected so that the pulse duration at the output of element DD3.4 is about 15 ms. Resistors R4, R5 are selected in the same way as R10, R11, but pulses with a duration of 1,2 ms must be applied to the input of the decoder. The distributor can work with any type of receiver. Information pulses at the output of the receiver must be negative with an amplitude of more than 1 V. The output of the receiver must be closed or have an output signal in TTL levels. Literature
Publication: N. Bolshakov, rf.atnn.ru
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