Street lighting machine. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting
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The scheme of the machine that allows you to automatically turn on and turn off street lighting in the morning is shown in Fig. 1.
The light sensor is a photoresistor R4. When it is dimmed, its resistance is high (several megaohms), at the inputs of the logic element DD1.1 - a high level voltage, the same voltage at the output of the element DD1.2. Transistor VT1 and trinistor VS1 are open, and street lights EL1 are turned on.
At dawn, the resistance of the photosensor R4 decreases, the logic elements DD1.1 and DD1.2 switch to opposite states, the transistor VT1 and the trinistor VS1 close and the street lights go out.
On logic elements DD1.1, DD1.2 and resistors R2, R3, a Schmitt trigger is made. This device, like a conventional (counting) trigger, has two stable states. But unlike the counting trigger, the state of which changes after the next pulse arrives at the input, the Schmitt trigger switches when the input voltage level changes. It is possible to choose resistors R2 and R3 in such a way that the switching thresholds with an increase in the input voltage and with its decrease will not be equal to each other. For example, for our trigger, when the input voltage increases, the switching threshold can be 3V, and when the voltage decreases, 2V. The difference in switching thresholds is called the trigger hysteresis. The greater the hysteresis, the greater the R2/R3 ratio.
If the Schmitt trigger is not used in the machine (i.e., the resistor R3 is excluded, and R2 is short-circuited), then when the illumination changes, the lighting lamps may flicker, while the output of the DD1.2 element will have a voltage between the low and high voltages . In the Schmitt trigger, this cannot be, since the feedback through the resistor R3 from the output of the DDL2 element to the input of the DD1.1 element will speed up the switching process, make it avalanche. Such feedback is called positive.
As a light sensor, you can use photoresistors FS-K (with any numbers), as well as photodiodes FD-1, FD-2, FD-3 (connected by cathode to resistors R1, R2).
The photo sensor should be located in a place where the direct light of the EL1 lamps does not fall, otherwise the machine will work unstably. Resistor R1 can change the level of illumination at which the illuminators turn on and off. The difference in the thresholds for turning on and off the lighting lamps can be changed by selecting the resistor R2.
The maximum power of lighting lamps is determined by the types of trinistor VS1 and diodes VD2-VD5. In this case, it is 2 kW. The trinistor and diodes are mounted on radiators.
See other articles Section Lighting.
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