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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Magic Relay. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches The automatic device can be used in various models, toys, which, when they encounter obstacles, will change their movement, as well as in everyday life (sat, for example, in an armchair - the light in the floor lamp came on, music played, the fan started); to turn on the light in the premises (corridor, room, pantry); for car alarms. Previously published capacitive relay circuits are quite complex, have large dimensions and a high level of interference radiation. Meanwhile, this device does not create interference within a radius of 4-5 m, has small dimensions (85x30 mm), is powered by a 9-12 V DC source, consuming a current of about 7 mA in the initial state, and up to 45 mA when the relay is triggered. . A schematic diagram of a capacitive relay is shown in Figure 1. A low-power generator with an operating frequency of 1 kHz is assembled on the transistor VT465, and an electronic key on the triode VT2 is used to turn on the relay K1, the contact system of which connects the actuator. Diode VD1 protects the device from accidental reversal of the polarity of the connected power source.
The range of the capacitive relay, that is, its sensitivity, depends on the setting of the capacitor C1 and the design of the sensor, and reaches 50 cm. Construction and details. The capacitive relay is assembled on a printed circuit board made of one-sided foil fiberglass or getinax 85x30 mm in size (Fig. 2).
Coil L1 is wound on a polystyrene frame from the circuits of DV (long waves) of transistor radios or on a self-made frame with a diameter of 7 mm, made of paper or other insulating material (Fig. 3). The distance between the "cheeks" is 1,5-2 mm. The coil contains 1100 turns (550 + 550) with a PEL or PEV 0,06 wire tap from the middle. Winding in bulk between the "cheeks" of the frame.
As a sensor, a piece of insulated wire with a diameter of 1,5-2 mm, a length of 15 to 100 cm, or a square or square lattice made of wire, with a side of 15 to 100 cm, is used. The sensor and the printed circuit board are located in close proximity to each other, and the wire or antenna plane is installed perpendicular to the printed circuit board area. The "minus" of the power supply must be connected to the body (metal) of the structure in which this capacitive relay will be used. Resistors, diode and coil L1 are mounted vertically on the printed circuit board. The parameters of the radio elements used in the device are not critical. The tuning capacitor is KPK-M, but another type can also be used with an interval of capacitance change from 3 to 30 pF. Oxide capacitors C2-C4 are used brand K50-6, but other types can be used, you just have to modify the PCB topology for them. Capacitances C2, C3 - from 20 to 30, C4 - from 50 to 1000 uF. Diode D226 can be with any letter index. You can also use another semiconductor device, designed for direct current up to 100 mA. Transistors: VT1 - field, brand KP303, VT2 - bipolar pnp type brand MP40 with any letter indices. Instead of the latter, the P13, P14, P15, P16, MP39, MP41, MP42 series with any letter indices and h213 are also suitable. K1 - relay RES10 (passport PC4.524.303). Instead, you can connect a small-sized electric motor for toys or a sound simulator ("meow", "cuckoo", "nightingale", etc.). Resistor R1 - any type of resistance from 6,8 to 7,5 MΩ. R2 - from 820 kOhm to 1,1 MΩ. The value of the resistor R3 is selected in the range from 0 to 30 ohms, depending on the current of the relay or electric motor. It is best to power the device in stationary conditions from a 9 V mains rectifier, rated for a current of up to 100 mA. To connect the power supply, grounding and actuator, pins made of copper wire with a diameter of 0,8-1 mm and a height of 5-7 mm are installed on the printed circuit board. For fastening in the board, 4 holes with a diameter of 3 mm are made. Establishment. Connect the sensor and a 9-12 V DC source to the board, observing the polarity. Using an insulated screwdriver, set the rotor of capacitor C1 (Fig. 4) to the position of minimum capacitance (6 pF) - this will activate the relay. Then slowly rotate the rotor C1 in the direction of increasing capacity until the moment when K1 turns off (when setting C1, try to stay as far away from the sensor as possible).
Bringing your hand to the sensor, test the sensitivity of the capacitive relay until the moment of self-operation (the smaller the capacitance C1, the greater the sensitivity of the device). Author: V.Tabunshchikov
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