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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Signal Arbiter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur What do you think is common between mathematics and electronics? Readers familiar with digital technology will probably remember that the mathematical laws of Boolean algebra underlie the operation of logic circuits. However, that's not all. It turns out that both in mathematics and in electronics they often operate with such a concept as comparison. But if you have to compare numerical values with each other, then in electronics there is a comparison of electrical signals. To perform such operations, even special devices have been created - comparators. It is curious that comparators are close "relatives" of triggers already familiar to us. What is their similarity? Firstly, the information at the outputs of these devices is encoded by only two logical levels - high and low; secondly, both of them switch from one logical state to another only in the presence of a certain combination of signals at the inputs. How are comparators arranged and what is the principle of operation? Let's digress for a while from our story and imagine a sporting event in athletics, for example, in running. After the athlete has reached the finish line, his result is compared with the record time for this distance. If the runner has not managed to exceed the world achievement, in such cases they say that "the record has stood." But if the time for which the athlete covered the distance turned out to be less than the record one, then the runner now becomes the record holder himself, and his result is now entered instead of the previous one in all sports reference books as the highest achievement. A similar situation can be seen, for example, in the operation of a simple comparator. This device has two inputs and an output. One of the inputs is most often supplied with a voltage or current that does not change over time, the so-called reference signal. A signal is compared with it, the level of which is unknown. Suppose we want to match the battery voltage from a flashlight to a fixed voltage applied to the reference input of a comparator. If the battery is heavily discharged and its voltage is below the reference, then no change will occur at the output of the comparator. But if the battery potential exceeds the reference voltage, the comparator will switch, and a signal different from the original will appear at its output. Isn't it true that the analogy with running competitions justifies itself. Judge for yourself. The input signal is less than the reference signal (the runner time is worse than the record one) - the logical state of the comparator does not change (the highest achievement remains the same). The input signal exceeds the reference signal (the result of the athlete is better than the world achievement) - the logical state of the comparator changes to the opposite (the record becomes higher). Thus, we can say that the comparator, as it were, plays the role of an arbitrator, determining which level of the signals turned out to be large. We have introduced you to the principle of operation of only one type of comparators. In fact, there are many more of them, differing in different ways. For example, comparators are often used in engineering, which can compare two continuously changing signals. Such a device switches from one logical state to another when the levels of the input signals match. There are comparators that, when the input signals coincide, produce a short single pulse or a series of a certain number of pulses that operate at the moment the polarities of the input signals coincide. Comparators are used in many areas of electronics. However, the most important area of their "activities" - devices whose operation is based on the conversion of analog signals into logic. Here is the simplest example - a digital voltmeter. One of its main nodes is a comparator that controls the operation of a pulse generator. Let's imagine that we want to determine the voltage at the output of a low-voltage mains power supply. How does the measuring device work in this case? The voltage of the power source is applied to one input of the comparator, and linearly changing to the second. Until they are equal, the generator generates pulses. At the moment when the voltages at the inputs of the comparator match, it will switch and the generation will stop. The pulses will be summed up by the voltmeter counters, and the result of the measurement will appear on its display. The generator of the device is configured in such a way that by the time the comparator is switched, the number of generated pulses will correspond to the numerical value of the measured voltage with an accuracy, for example, to tenths or hundredths of a volt. From the above, it is easy to conclude that comparators have successfully combined the properties of analog and digital devices, and their main purpose is signal conversion. A simple comparator can be assembled on an operational amplifier. A diagram of such a device is shown in Figure 1.
A reference voltage is applied to the inverting input of the op-amp through the limiting resistor R1. The non-inverting input plays the role measuring. The signal is fed to it through the limiting resistor R2. To turn the op-amp into a comparator, a feedback circuit formed by resistor R3 is introduced into the circuit. The principle of operation of such a device is simple. In the initial state, the voltage at the output of the operational amplifier is zero. If a voltage is applied to the measuring input of the comparator, the value of which is less than the reference voltage, then the state of the op-amp will not change. When the voltage at the measuring input of the device exceeds the reference, the output voltage will begin to increase. Through the feedback circuit, it will go to the measuring input, which, in turn, will lead to an increase in the input current. As a result, the output voltage will increase even more. In short, the process becomes an avalanche and the voltage at the output of the op-amp will increase abruptly to a maximum level. Thus, the comparator will switch from the "zero" state to the "single" state. Isn't it all very simple? Well, now that we have got acquainted with the device and the principle of operation of comparators, we can proceed to their practical application. To do this, we suggest you assemble a simple electronic game. It is based on guessing by one opponent the actions of another. Two people participate in the competition. So, imagine a small box with a light indicator, a pushbutton switch, a toggle switch, and an electrical measuring device, such as a voltmeter, installed on the front panel. This is the main block. It is connected to two remote control, equipped with regulators. Having distributed the roles, the participants begin the game. It begins with the fact that the driver takes his remote control and turns the regulator to an arbitrary angle (within the limit of free play). The second player does not see these actions. His task is to repeat the opponent's move as accurately as possible. Let's say there are three tries. The guesser takes his remote control and turns the knob to the desired angle, in his opinion. Then he presses a button and evaluates his move. If the indicator light comes on, it means that the knob is not turned enough. The absence of a light signal indicates that the regulator is turned more than necessary. Further, the guesser decides what to him; now do - turn the knob forward (if the indicator is on) or back (if the indicator is off). Having made one more attempt, he again presses the button and evaluates his second move by the state of the indicator. Then he turns the knob a third time and now turns on the toggle switch. In this case, the voltmeter will prove the final result of the game. If the arrow remained at zero, it means that the guesser accurately “calculated the opponent’s move. If it deviated from its original position, the driver’s intention remained unsolved. The greater the deviation of the voltmeter needle, the more advantage the driver wins. Periodically changing roles, players can compete with each other, and then compare who has developed intuitive flair. better. If there are many people who want to take part in the competition, it can be held in a round robin system, a table of results can be compiled and the winner can be determined from it. In a word, you can find a lot of options for using this slot machine, the main thing is to show a little imagination and fiction. Note that the device has a peculiarity - it shows the final result, the value of which, in a strict mathematical language, is taken modulo, that is, without taking into account the sign of the difference. To define it; additional button must be pressed. If the indicator is not lit, it means that the second player has busted. When the indicator is lit, it means that the guesser "didn't reach" the opponent's result. So, having understood the rules of the game, you can get acquainted with the contents of the slot machine. Its schematic diagram is shown in Figure 2.
As expected, the "heart" of such a device is a comparator. It is assembled according to the scheme already familiar to us on the operational amplifier DA1. Resistors R4, R5 and R10 limit the input and output currents of the microcircuit, protecting it from overload, and R8 forms a feedback circuit. As an indicator, the HL1 LED is used, which is turned on by the SB1 button. The role of the measuring device is performed by a DC voltmeter PV1, installed in the diagonal of the rectifier bridge VD1-VD4. Its arms are connected, in turn, between the inputs of the comparator. The measuring circuit of the voltmeter is switched by the SA1 toggle switch. Resistors R1, R3, R7 and R2, R6, R9 form two controlled voltage dividers. In this case, the variable resistors R3 and R6 perform the functions of regulators installed in the consoles. How does a slot machine work? Let's say the driver took the first remote and set the variable resistor R3 to the middle position. In this case, the voltage from the top divider according to the circuit will go to the reference input of the comparator (inverting input of the op-amp) and simultaneously to the diodes VD3, VD4 of the rectifier bridge. Now the guesser comes into play. He takes his remote control and turns the variable resistor R6. As a result, the voltage from the lower divider according to the circuit is supplied to the measuring input of the comparator (non-inverting input of the op-amp) and simultaneously to the diodes VD1, VD2. If the voltage level at pin 10 of DA1 is lower than at pin 9, the operational amplifier will be in the "zero" state. By pressing the SB1 button, the player is convinced of this by the glow of the HL1 indicator. If the voltage at the measuring input of the comparator exceeds the voltage at the reference input, then the op-amp will switch to the opposite state, and a logical unit will appear at its output: the LED will not light. It should be noted that the switching of the operational amplifier occurs when the measured voltage exceeds the reference voltage by about 0,3 V. Thus, with the exact match of the input voltages (and, consequently, the positions of the regulators R3 and R6), H1.1 continues to burn. When participating in the game, do not forget about it. After all the attempts of the second player are exhausted, he turns on the BA1 toggle switch. If the voltage levels on both wires of the comparator are completely the same, the voltmeter needle, as we have already said, will remain at the zero mark of the scale. If the voltage at one of the inputs exceeds the voltage at the other input, the needle will deviate from zero and show the difference in input voltages. Since the device is included in the diagonal of the rectifier bridge, it does not matter which of the inputs of the op-amp has a higher voltage level. The voltage polarity on the voltmeter will always be the same. Naturally, the arrow of the device also deviates only in one direction. To determine on whose remote control the knob is turned more at the end of the game, as we have already suggested, you can press the BV1 button and draw the final conclusion based on the state of the HL1 indicator. The gaming machine is powered by a network stabilized source with a so-called artificial midpoint (Fig. 3).
If the K140UD1B chip is used in the design, then the output voltage of the power source should be 12 V. When using the K140UD14 IC, the voltage must be reduced to 9 V. The brand of the zener diode for the latter case is indicated in brackets in the diagram. The manufacture of a gaming machine begins with a circuit board shown in Figure 4. It is best made from a sheet of foil-coated getinax or fiberglass 1-2 mm thick, 35x30 mm in size.
Drill two fixing holes Ø 3 mm from one end. The elements of the power supply are placed on a circuit board with dimensions of 75x30 mm, made of the same foil material (Fig. 5). The transistor does not need a heatsink.
About the details. Operational amplifier - K140UD1B or K140UD1 A. Transistor - any of the KT601 series - KT603, KT801, KTV05, KT815, KT817, KT819. For a power supply with a voltage of 12 V, a Zener diode D811, D813, D814G, D814D or KS211 is suitable. If the supply voltage needs to be reduced to 9 V, you can use the Zener diode D809, D810, D818A-D818G, D814B or D814V. Diodes - Uy4 - any of the series D2, D7, D9, D1V, D20, D206, D220, D223, D226, D237. Rectifier unit - KTs405 with any letter index or four medium power diodes connected in a bridge circuit. LED brand AL 102 or AL307. DC voltmeter - with a measurement limit of 5-6 V. If this was not found, then a milliammeter with a series-connected limiting resistor of the required resistance can be used as a measuring device. Capacitor C1 - K50-6 or K50-16, C2 and C3 - K50-24. Fixed and variable resistors - any brand. The network transformer is low-power with a secondary winding voltage of 12-18 V. The H1-2 lamp is of the MN-2 or MN-3 brand. Toggle switches and push button switch - any type. The fuse must be designed for a current of not more than 0,5 A. ХР1 - a standard mains plug. The appearance of the gaming machine is shown in Figure 6. The case for it can be made of plastic, plywood or aluminum. A ready-made one, for example, a plastic box from under the threads, is also suitable. On the front panel of the device, fix the measuring device, toggle switches, push-button switch, LED and neon lamp. Install a fuse holder on one of the side walls. Apply appropriate markings near the controls. Mount the circuit boards and the power transformer to the base of the case. Solder the resistor R11 directly to one of the neon pins. Make all necessary connections with thin, insulated stranded wires.
Drill three holes on the rear wall of the case: one for the network cable, and the other two for the cords connecting the device with remote controls. Ordinary soap dishes are suitable as cases for them. Provide variable resistors with decorative handles. For greater convenience, several labels can be applied around each regulator - it is easier to navigate through them when calculating your actions. The slot machine does not require adjustment. If you did not make mistakes in installation and used serviceable parts, you can be sure of its performance. Author: V. Yantsev
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