Solar light indicator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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It will take only a few parts and a little time to assemble a light indicator. It is useful for comparing the brightness of lighting lamps, the illumination of workplaces, and if its scale is calibrated in units of illumination according to a reference device, then it can also be used as a meter. It should be recalled that the unit of illumination in the International System of Units is lux (lx), 1 lx = 1 lm / m². Lighting is one of the natural conditions of life, which is necessary for health and high productivity. Insufficient, as well as excessive, illumination negatively affects human performance. Lack reduces attention, drowsiness appears, excess excites, increases fatigue. The table shows the average light levels in different situations.

The indicator scheme is shown in fig. 1. Its base is a rechargeable LED lawn light. From it the case and the solar battery are used. The use of a solar battery as a light sensor made it possible to make the device without a power source, and therefore it is always ready for operation.

Rice. 1. Indicator scheme

The device uses the property of a solar battery, which consists in the fact that the short-circuit current (SC) directly depends on its illumination. To create a mode close to the short circuit mode, it is necessary to connect such a load to the solar battery so that the output current is determined by its internal resistance. Since the maximum voltage (EMF) of the applied solar battery is 2,4 ... 2,5 V, by connecting a load at which the output voltage would not exceed 0,2 ... 0,3 V, a mode close to a short circuit can be obtained. This can be done with a microammeter and shunt resistors to achieve multiple subranges.

The indicator uses a small-sized microammeter with a total deflection current of 100 μA and a coil resistance of 2,6 kOhm. Therefore, the voltage on it when the arrow deviates to full scale is 0,26 V. Resistors R1 and R2, which are connected in parallel to the microammeter using switch SA1, expand the current measurement limits to 1 and 10 mA. Fixed resistors MLT, S2-23 and similar are used, the switch is any small-sized, for example, sliding, any microammeter can be used with a total deviation current of not more than 150 ... 200 μA, the dimensions of the indicator part depend on its design.

The device consists of two parts, a sensor and an indicator, connected by a two-wire cable 1 ... 1,5 m long. A lamp with a cylindrical body with a diameter of 45 mm was used, the dimensions of the solar battery were 25x25 mm. All "electronics", except for the solar battery, is removed, and the height of the case is reduced to 10 mm (Fig. 2). The microammeter, switch and resistors are placed in the diffuser (Fig. 3). To do this, a rectangular hole is made in its side wall for the switch engine, to the conclusions of which resistors are soldered. To give a "commodity" look, the diffuser is painted with black paint. The appearance of the device is shown in fig. 4.

Rice. 2. Housing

Rice. 3. Microammeter, switch and resistors

Rice. 4. Appearance of the device

Establishment comes down to a selection of resistors R1 and R2. To do this, a microammeter through a resistor with a resistance of 1 kOhm and a reference ammeter (multimeter in current measurement mode) is connected to a laboratory power supply with an output voltage of 0 ... device. Resistor R15 is connected and the output voltage of the unit is increased, setting the current ten times more, and by selecting this resistor, the arrow is set to the maximum mark on the scale. Perform a similar operation by connecting the resistor R0 (pick it up) and setting the current ten times more. The adjustment procedure can be simplified by replacing the fixed resistors with trimmers, for example SP1-1 (R2 = 3 ohms, R19 = 1 ohms).

The light sensor must be positioned perpendicular to the incident light. When light rays fall obliquely, the illumination decreases in proportion to the cosine of the angle of incidence.

Author: I. Nechaev

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