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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Humidity, light and water level sensor on the timer KR1006VI1 (NE555). Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology To signal a violation of a parameter in production and at home, electromagnetic relays connected to electronic circuits are used. The contacts of electromagnetic relays work more durable if the winding is powered in the "trigger" mode - a sharp supply and a sharp removal of voltage, while it is desirable to reduce the number of switching on and "bounce" is completely undesirable - pulsed power supply of the relay winding. The timer on the KR1006VI1 chip is well suited for such purposes for the following reasons:
Thus, two threshold devices, a trigger and two powerful outputs with a small package size allow you to assemble good devices, but we will focus on a relay device - a converter of a weak and slowly changing signal into sharply changing two states to control the output relay. Figure 1 shows a diagram of a moisture detector. The scheme is suitable for controlling the moment of deposition of moisture droplets on the hygristor sensor R'. The simplest sensor can be made from foil fiberglass by cutting out two tracks in a zigzag pattern. The best results will be if you cover these tracks with silver or use a fluoroplastic plate and stainless electrodes pressed against it. To better "catch" the increase in air humidity, you can place the sensor electrodes in a bag of calcium chloride (or at least table salt). Place the sensor in a cooler place. Resistor R1 sets the threshold for the circuit (relay armature pull). Switching off the circuit (releasing the relay) occurs at a higher resistance of the sensor, so the relay will not operate too often.
Resistor R2 limits the adjustment limit of R1 to "zero", R3 limits the current at the input of the circuit from the sensor during installation, emergency situations. Capacitor C1 (with good insulation!) Smooths out the input signal, as well as interference from the network. It is advisable to always use the VD1 zener diode in circuits with the KR1006VI1 timer - this will allow you to safely mount and set up the device: the zener diode limits the voltage at the timer inputs from + stabilization voltage to - 0,6 V. The zener diode can withstand current up to 30 mA, and the input resistor has a resistance of 50 kOhm . Conclusion: input voltage up to 1500 V will not harm the timer (and the input resistor will fail). Capacitor C2 smooths out the potential of pin 5 of the microcircuit, which is "involved" in the comparator comparison circuits, so its use is mandatory. Diode VD2, turned on "back" to power, removes current surges at the moment the relay winding is turned off. The power supply of the circuit must be stabilized (the microcircuit can normally operate in the range of 5-16V power supply. The photo relay (Fig. 2) contains an input stage on a field-effect transistor with an insulated gate. This increases the input resistance to billions of ohms and allows you to include not only semiconductor photoresistors, but also vacuum photocells, the stability of whose parameters with temperature changes is higher than that of semiconductor ones. Of course, by reducing the resistance of the resistor R1 even to 10 kOhm, you can adjust the input of the circuit to the resistance of the photosensor at the moment the output relay is triggered. A circuit with a voltage follower on a field-effect transistor allows, by adjusting the resistance of the resistor R6, to “bring together” the edges of the interval for switching on (off) the relay.
If in the circuit (Fig. 1) the moment of operation of the relay satisfies the user, and turning off (return) requires a large change in the input potential, then in the circuit (Fig. 2) by increasing the resistance of the resistor R6, you can arbitrarily narrow the "differential" between switching on and off. The possibility of such an adjustment makes it possible to turn the parameter violation signaling device into a regulator that maintains the parameter in a certain interval near the norm. To control or regulate the temperature, it is necessary to include a temperature sensor - a thermistor, diode or transistor (Fig. 2) at the input of the circuit in Fig. 3. A semiconductor decreases resistance as the temperature rises. If heating the diode by 10 ° C leads to an approximately twofold decrease in resistance, then heating the transistor leads to a fourfold decrease. The germanium semiconductor "feels" the temperature more strongly, but the silicon one can operate at higher temperatures (up to 150 ° C). It is better to install transistors in which the case is connected to the collector, and the emitter is supplied with positive power, then there will be no problems with isolating the "input" point from the circuit case.
To increase the speed of the circuit, a tinned sheet heatsink can be soldered to the transistor case. If soldering is carried out with a powerful soldering iron and the transistor is quickly cooled with air, even germanium devices will not be damaged. With such a temperature sensor, the 9th expedition of the Vinnitsa region. measured the air temperature during observations of the solar eclipse in 1981 in the Novosibirsk region. Comment. The terminals of transistors in metal cases are insulated with glass insulators. Check whether the illumination of the leads by sunlight will cause the circuit to operate, if necessary, wrap them with black thread and cover them with glue. If the resistance of the temperature sensor is not very high, the field-effect transistor can be replaced with a bipolar one with a high gain, for example, KT3442B, this will reduce installation difficulties. When connecting the contacts of the output relay in the diagrams (Fig. 1 and 2), it should be taken into account that the relay closes when humidity, temperature, and illumination increase and opens when they decrease. Thus, if the circuit in Fig. 2 controls the circuit of the automatic fire extinguisher, the make contacts of the relay should be used. If the circuit controls the electric lamp-heater in the drying cabinet, it is necessary to use the NC relay contact The presence of two comparators as part of the timer chip allows you to perform a simple circuit for controlling the water supply pump (Fig. 4). The circuit is designed for pumping water out of the tank (the tank filling circuit uses a break contact in the output relay). When the lower level electrode E1 is soaked with water, a voltage approximately equal to half the supply voltage acts at the input of the circuit (such a voltage cannot switch the output of the microcircuit), due to the same resistances of resistors R1 and R2. Depending on the temperature of the water, the material of the electrode, the emerging EMF can slightly distort this voltage, then you will have to change the value of the resistor R2.
With a further increase in the water level and the soaking of the electrode E2 at the input of the circuit, the voltage decreases lower than the third part of the supply voltage. This causes the circuit to switch and the output relay to operate! The water level decreases, but as long as E1 is in the water, the state of the circuit does not change. The loss of contact between E1 and water leads to an increase in the voltage at the input of the circuit above 2/3 of the supply voltage, as a result of which the internal trigger of the microcircuit switches and the relay is de-energized. To tune the circuit, the following circumstance is essential: it is necessary to tune at the lowest water temperature and the lowest concentration of conductive impurities. The capacitance of the capacitor C1 is chosen relatively large so that the network pickup on the wire going to the input of the circuit is suppressed. This capacitor is better to install non-electrolytic. Resistor R2, which connects the electrode leads to each other, should be installed on a fiberglass board, which is fixed to one of the electrodes (to the electrode terminal). The flexible lead is connected by an insulated conductor to the second electrode. It is necessary to protect the resistor from moisture and mechanical influences. Unlike most circuits of water level indicators, this circuit not only saves one core of the cable, which simplifies setup and installation, but also suppresses AC voltage interference at the circuit input, including impulse noise (which is currently used in existing installations with industrial level indicators). often cause problems). By increasing the ratings of R3 and C1, you can even "delay" the relay operation time by several minutes, then any impulse pickups will not be able to cause false tripping of the circuit. In addition, the microcircuit has one more input terminal (pin 4), the closure of which "resets" the timer output to 0, regardless of the input potentials (pins 2 and 6). Usually this pin 4 is connected to the supply voltage so that the input does not affect the operation of the circuit. Another interesting application can be obtained by a relay device if its input is equipped with a double (differential) light or temperature sensor. In this case, the output relay is activated when the light/shadow boundary passes through the double sensor. To eliminate false positives, as well as to protect against high illumination of two sensors, it is necessary to install two resistors R1 - to limit the current of "own" photosensor and R2 - to add the "initial" current to the shoulder of "own" photosensor. Such a circuit, in the case of illumination of two sensors with bright light, gives the input of the relay circuit a potential close to the limit values of R2 and R. would lead to an indefinite signal at the input of the circuit.And only in the case of not too much illumination of the photo sensors, under the condition of greater illumination R ', the relay device switches to the required state (depending on which input option in Fig. 5 suits us). Such an unusual connection of sensors makes it easy to make a photo shooting target. In the central zone there is one photoresistor, and around it there are four, connected in parallel, only the "hit" of light in the central zone will trigger the output relay! If the resistor R3 is shunted with a silicon diode, then, depending on its polarity, the circuit will go faster to one state and slower to another. By selecting R3 and C1, it is possible to delay the operation of the relay from a short flash of light for a while. It will not be difficult to make an alarm clock for a fisherman, triggered by the light of the moon. To do this, you need to point the protective tube of the photo sensors to the place where the Moon will appear at a certain time of the night, so that one sensor is illuminated earlier and the other later. If the night is moonless or cloudy, the "alarm clock" will not work!
Light and temperature sensors can be devices with different resistance - the range of circuit tuning is huge. In the case of a differential sensor, it is desirable to use photo or thermal devices from the same box, i.e. devices manufactured and stored in the same way. The few applications mentioned do not cover the entire range of applications for bottom relay circuits. Indeed, by changing the time constant of the input circuit and installing a high-frequency transistor instead of an electromagnetic relay at the output, it is possible to make the circuit operate at frequencies up to a megahertz (depending on the input sensor). This means that it is possible to make a TV remote control device from a long distance, using a differential photo sensor - and "secret" control. In a similar way, it is possible to open the door of an object with an infrared impulse "key", directing a focused beam to a certain point - this increases the degree of protection of the object. With good road markings, a differential sensor with an illuminator could “follow” the marking strip and give the driver an audible signal at the moment of blinding from an oncoming car, so that the driver could “not fly off” the road for a couple of seconds, but continue driving further. But this requires duplication of sensors and the use of a different scheme. A circuit with a differential photosensor and a properly selected time constant of the input circuit can, with the help of an electric motor, turn the solar light or heat receiver following the movement of the luminary. Author: N.P. Goreiko
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