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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Autoindicator with one lamp. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices At one time, various designs of voltage indicators were very popular among radio amateurs. And this is not surprising - with their relative simplicity and minimum costs, you can quickly get a "visible" result. As for motorists, then, according to the observations of the author, such designs did not arouse interest in them. They required alteration of the car's dashboard or placement of a separate unit on it, besides, they distracted the driver's attention. On the other hand, motorists did not see the need to redo anything in this regard, since they completely relied on standard instruments: an ammeter, voltmeter and / or a control lamp. Meanwhile, the control lamp and the ammeter in most cases register only the direction of the current in the "Battery (AB) - generator" system and do not allow one to judge the qualitative changes in it. The author reviewed publications on this topic over the past 20 years or so and came to the conclusion that the most successful design is still E. Klimchuk's voltage indicator [1]. The specified indicator works with one regular control lamp, which is available on almost any vehicle, including motorcycles. At the same time, it allows registering with a high degree of accuracy the four main modes of operation of the "AB-generator" system. Such a number of modes, as practice shows, is optimal. By the way, the driver practically does not need to change the psychology of perception: two more clearly distinguishable generator modes are added to the usual modes of operation of the control lamp. As for the usefulness of this indicator, the case that happened to the author is very curious. On the road in a GAZ-2410 car, the control lamp began to flash, moreover, at the moments when the car was shaken on potholes. Checking the tension of the alternator drive belt did not give any results. And only an inspection of the car in the pit revealed an unexpected malfunction - the loss of the lower generator mounting bolt. Since the generator bottom rested against the engine, the belt was not loosened. However, on the roughness of the road, obviously, the upper bar of the generator mount began to "play", and there was a short-term slippage of the belt. This was enough to register voltage dips. The most curious thing is that for a long time the release of this model, a control lamp was installed on it, which lit up only when the dashboard lamp test button was pressed. No device for controlling its operation was provided by the plant. The presence of an ammeter with a scale length of about 40 mm and a maximum deflection current of ±50 A turned out to be useless in practice. For example, before the indicator was installed, the failure of the voltage regulator was noticed too late, when the battery was already almost completely discharged. The indicated voltage indicator has been working reliably on the car so far. Since publications on this topic continue to appear in the amateur radio literature (for example, [2]), I want to return once again to a well-proven design. In the new version of the indicator, the digital part has been completely changed. The basis of the proposed indicator circuit (Fig. 1), as in the prototype, is a dual voltage comparator assembled on the DA1 chip. Its only difference is the use of a low (rather than high) voltage level to obtain an additional logical combination, which increases the stability of the generated voltage threshold. The voltage at the non-inverting inputs of the comparators is stabilized by the parametric stabilizer VD1-R5. The applied DA1 chip is operable in a wide range of input voltages (from 0 to 32 V), but for the correct operation of the comparator, it is necessary that the voltage at one of the inputs of each op-amp be at least 1,5 V less than the supply voltage (excluding the voltage drop across resistor R11), which is ensured by the corresponding inclusion of the zener diode VD1.
The voltages at the inverting inputs of the comparators are set during tuning by the dividers R1-R2 and R3-R4. For the DA1.1 comparator, the voltage at the inverting input, due to the connection with the DA1.2 output through the VD2-R9 chain, can take two values. Thus, as the supply voltage increases, four logical combinations are sequentially formed at the outputs of the comparators: 00, 10, 01, 11. In accordance with these combinations, the digital part of the indicator provides 4 modes of operation of the control lamp. The indicator operation algorithm proposed by E. Klimchuk turned out to be very successful in practice. A higher frequency of operation of the indicator lamp instantly signals a dangerous voltage in the on-board network, and a lower frequency warns of an unacceptable degree of battery discharge. The digital part of the indicator is built on an inexpensive timer DD2 (MC14541B), the pin assignment of which is given in Table 1.
The presence of a built-in generator and a counter with a variable division factor makes it possible to abandon two low-frequency generators and use capacitor C3 with a better TKE or smaller dimensions as a frequency-setting element. The choice of the division factor depends on the two-digit code at the address inputs A and B of the timer. As can be seen from Table 2, division ratios of 256 and 1024 are suitable for obtaining two visually distinguishable generator modes of the lamp, since they provide a difference between the frequencies at the output of the timer by a factor of 4.
Unfortunately, the logical levels at the outputs of a dual comparator do not allow one to immediately obtain the desired sequence of timer operation modes (Table 3). Therefore, EXCLUSIVE OR elements are introduced into the circuit (chip DD1). At different logic levels at the outputs of the comparators, the DD1.2 element generates a high logic level, which resets the internal timer counter and stops the generator. In this state of the timer, its output voltage matches the logic level at the SE input. Accordingly, the lamp is either on or off. The required switching order of the lamp corresponds to the logic level at the output of the comparator DA1.1. In the extreme modes of the indicator (at the input MR - "0"), the internal timer generator starts to work. The generation frequency at the output of the timer depends on the logical combination at the inputs A and B. Since in this mode the logic levels at the outputs of the comparators are the same and match the required level at the input A of the timer, then for input B the signal is inverted by element DD1.1.
The logical levels marked with an asterisk in Table 3 were not chosen by chance. Although they do not affect the operation of the indicator as a whole, it is still preferable that the levels on inputs A and B are already set before the generator starts to work in order to avoid unnecessary "bounce" inside the timer. The levels indicated in the table at the SE input allow you to start the generator mode with an instant switching of the lamp, without waiting for the first pulse to appear. So, if the lamp was turned off in the previous state, the generator mode will begin with its ignition, and vice versa. A sound generator is assembled on the elements DD1.3 and DD1.4. Its inclusion occurs only in the generator operating modes of the indicator when there is a level of "0" at input 12 and "1" at input 8. Therefore, extreme modes can be distinguished by ear. This circuit is designed for vehicles in which the control lamp is connected to the "+" power source (through the ignition switch contacts). Meanwhile, on some older models, for example, the VAZ-2101, the control lamp on the dashboard is to disassemble the instrument panel, in this case it is enough to replace the transistor VT1 with KT973A, and to invert the output signal of the timer, add the transistor VT2 (Fig. 2). In this case, the emitter of the transistor VT1 must be connected to the "+" power supply through the ignition switch, and the collector - with a free lamp outlet (both wires on the above model are brought to the engine compartment). Resistor R17, shown in Fig. 2 by a dotted line, may be needed when using transistors of a different type as VT1, for example, KT814, KT816. The composite transistor KT973A already has such a resistor.
The printed circuit board of the device (Fig. 3) is made of one-sided foil fiberglass and is designed for both options for connecting a control lamp. In the first option, it is necessary to bridge the contact pads blackened in Fig. 3 with a jumper, in the second one, additional details must be installed: transistor VT2, resistor R16 and, if necessary, R17, which is soldered directly on the terminals of the transistor VT1 or on the board from the printed conductors. In the latter case, it is convenient to use this method. At a resistor with a rated power of 0,125 W, bite off the leads and remove the protective paint from the end cups. The cups are cleaned with fine sandpaper, for example, by holding a resistor in a microdrill chuck. The resistor prepared in this way is soldered with cups to the pads of the board or to the terminals of the transistor.
Zener diode VD1 and resistor R7 are installed on the board before mounting the DA1 chip. Capacitor C1 - K53-1A, the rest - any ceramic. Free pins 4 and 11 of the DD2 chip are best removed. Although they are just a technological part of the case, the presence of any signals on them is undesirable. The piezo emitter HA1 may be of another type. It is advisable to start setting up the indicator by setting the comparator thresholds, i.e. supply voltage (AB) at which the control lamp operation modes change Upor.1...Upor.3. This requires a power supply with a continuously adjustable output voltage of 10 ... 15 V, a digital multimeter and, preferably, an oscilloscope. The resistors that determine the comparation thresholds (R2, R4 and R9) are set as they are selected. First, instead of R4, a tuning resistor (preferably a multi-turn) is soldered and, by setting the voltage at the "AB" terminals of the circuit, equal to Upor.3, by rotating the R4 engine, they achieve switching of the DA1.1 comparator, controlling the voltage at its output using an oscilloscope. Then the voltage is smoothly changed, specifying the upper and lower switching thresholds DA1, because comparators for more precise switching are covered by positive feedback through the chains R6-R8 and R7-R10. It is better to do this operation several times, changing Upores. After that, the tuning resistor is soldered, its resistance is measured and replaced with a constant with the same value. In principle, the selected resistor can be made up of two. The use of trimmers is not recommended. Then the resistor R2 is selected in the same way at the supply voltage Upor.2. seeking to switch the comparator DA1.2. And in conclusion, they select R9, seeking to switch the comparator DA1.1, but already at the supply voltage Upor.1 The resistance R15 in the sound generator may differ from that indicated in the diagram, especially if a different type of piezo emitter is used. It is selected according to the maximum volume of the piezo emitter. Voltage Upor.2 and Upor.3 it is advisable to choose equal to the extreme values of the range provided by the voltage regulator. This range is usually indicated in the operating manual for the car or in the passport for the voltage regulator. It should be noted that in industrial voltage regulators, the specified range, as a rule, corresponds to the technological spread of parameters during production, and not to the actual change in voltage from temperature. When the indicator is operated with a fully thermally compensated voltage regulator, the choice of the specified comparation thresholds becomes more complicated. Therefore, we can simply recommend radio amateurs to choose Upor.2 = 13,6 V, Upor.3 \u14,6d XNUMX V. Most industrial voltage regulators fit into the specified range. As for temperature-compensated voltage regulators, the indicator works for me in conjunction with a voltage regulator [3]. In cold weather (about -30°C), when the engine is started, the control lamp starts flashing at an increased frequency, signaling a high voltage (as you know, at low temperatures, the voltage at the battery terminals must be increased). After warming up the engine compartment, and therefore the battery, the lamp goes out. Initially, this behavior of the lamp caused alarm, but very soon this mode became even convenient - it indicates the performance of the thermal compensator. In moderate weather, the indicator works normally. With choice Upor.1 the matter is even more complicated. At first glance, you can install Upor.1, corresponding to 50% of the degree of discharge of the battery (as is known, the voltage is related to the density of the electrolyte in an almost linear relationship). But this voltage is highly dependent on the temperature of the electrolyte. There is another important factor as well. Let me remind you that in order to increase the measurement accuracy, the indicator should be powered directly from the AB terminals. The control lamp turns on when the ignition switch is turned. At the same time, a significant load is also connected to the battery - the excitation winding of the generator (the current through the primary winding of the ignition coil is not excluded). You can, of course, use a separate switch to power the lamp, but this is not very convenient. It is better in the design of the voltage regulator to provide for the inclusion of the excitation winding after the engine is started [4] or even after the engine reaches the minimum speed required to excite the generator [5]. You can also do this: select a day with an average temperature, discharge the AB load plug to the desired level and install it on the car. After that, turn the ignition key (without starting the engine) and measure the voltage at the battery terminals with a digital voltmeter. On the received value and adjust Upor.1. As a last resort, you can recommend Upor.1 = 12,0...12,6 V. Structurally, the voltage indicator is made as described in [6]. The indicator housing serves as a common wire. It is better to install the indicator in the passenger compartment, avoiding proximity to the heater. The conductor connecting the indicator to the AB should be soldered to the board (without a connector), and at the other end, solder a petal under the AB terminal. To facilitate the removal of the battery from the car, the petal can be put on the starter terminal connected by a "powerful" wire to the "+" terminal of the battery. The proposed circuit is operable in the supply voltage range from 3 to 18 V. The temperature range depends on the design of the DA1 chip and ranges from 0°С to +70°С (LM358) and from -55°С to +125°С (LM158). Literature
Author: A.Martemyanov, Seversk; Publication: radioradar.net
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