Automatic backlight device with house number. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Automatic backlight device with house number. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Lighting

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The figure shows the appearance of an automatic lamp that works when the working surface is darkened.

Automatic lighting device with house number

The practical application of the device is in the automatic switching on of the illumination of the plate with the name of the street and the house number. The incandescent lamp is installed inside the plastic case of the plate with the house number, and the elements of the device are installed in the wall of the house in a closed case protected from moisture. In normal lighting (when it is light outside), the lamp does not light. At dusk, the level of natural light drops and the incandescent lamp lights up, illuminating the sign. The photoelectric sensor is a photoresistor, which receives an external light flux through the lens.

PR1 - RFT-01 brand photoresistor, used as a photosensor in Arctur-004 turntable rotation controller. Instead, as a photoresistor, it is also permissible to use photoresistors installed in OEP-1 optocouplers. When the photoresistor is illuminated (bright sunlight), its resistance drops to 12 kOhm and shunts the transition "control electrode - cathode" of the thyristor VS1. In this case, the thyristor closes and de-energizes the incandescent lamp EL1. For such illumination, a low-power lamp is sufficient. It is impossible to use a more powerful incandescent lamp in the device because of the danger of overheating and melting of the plastic case of the plate.

With a 1 W incandescent lamp (to illuminate refrigerators, sewing machines and illuminate other household appliances), the device was operated for two days (with the EL1 lamp constantly turned on), while the temperature around the lamp bulb did not rise above +35 ° С, which is quite acceptable . If the sensor is not sufficiently illuminated (which happens at night), the resistance of the photoresistor is high (more than 1 MΩ). The current passing through the limiting resistor R1 is sufficient to open the thyristor.

Establishment. To increase the photosensitivity of the node, you can replace the fixed resistor R1 with an equivalent circuit, as shown in Fig. 2.12 (below), by entering the sensitivity adjustment into the electronic assembly. So, by changing the resistance of the resistor R1, an increase or decrease in the current through R1 is achieved, respectively. For the same reason, there will be potential changes at the midpoint of the voltage divider R1PR1. With an increase in current through R1 (a decrease in its resistance), the sensitivity of the node to external darkness increases many times over. Now the lamp works faster at dusk (turns on the backlight).

With a decrease in the current through the resistor R1 (increase in its resistance), the opposite will happen - the lamp becomes more sensitive to external lighting and turns off the backlight even with a small impact on the working surface of the light flux photosensor. Any variable resistor is used in the process of setting the sensitivity threshold (after adjustment, having measured its equivalent resistance, R1 is replaced by a constant one). To retain the ability to adjust, a multi-turn variable resistor SPZ-1BV or a similar compact tuning resistor is suitable.

The phasing of the connection to the 220 V network is not important for the device.

About details. Thyristor VS1 is used of the MCR-106-8 type (marked MCR-106 in the diagram). It can be replaced with other Motorola thyristors. This designation is not given by chance, since the thyristor for this circuit can be chosen and another one, guided by reference materials on the electrical characteristics of thyristors and triacs from Motorola (located in the appendix to the book).

Capacitor C1 of the MBM type or similar for an operating voltage of at least 300 V. When the load power increases by more than 60 W, it is necessary to install a thyristor on the heat sink.

The electrical circuit can be assembled independently for use in other designs as a simple photo relay. In doing so, the following points are taken into account.

Thyristor VS1 is replaced by a domestic triac KU208G.

The fixed resistor R2 is excluded from the circuit, a jumper is installed instead. Resistor R1 is replaced by another with a dissipation power of 2 W and a resistance of 12-18 kOhm. Or an equivalent circuit (if sensitivity and threshold adjustment of the photorelay is required) with the same total resistance. Photoresistor PR1 is the same as in the basic circuit. When replacing it with a different type, the resistance of the resistor R1 will have to be selected additionally and within other limits.

See other articles Section Lighting.

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