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Photo relay - automatic lighting control
When to automatically turn on or turn off the electricity In cases for example the illumination of streets and squares in the dark. Or for example in greenhouses or in the apartment, everywhere where there is light and need to turn it on, there are many options on how to do this The need to control the lighting has always been and will remain relevant in any season and under any conditions. Photo sensors is one of the real devices that allows you to control lighting by analyzing the light level in a particular location or on the lot or on the roadway. Photo relay is typically scheme, consisting of a light receiver and a key device. From the light-receiver signal, the device in one position, if not, it switches to another, thus either there is a light on the pole when the night, or no if its a clear day. Schemes under this direction very much, radio designers create them almost on the fly, the main thing is to have a good photo diode and not difficult to assemble transistor switch in the load circuit which turn on the relay control circuit 220. Will you the simple system, this scheme is a weekend, will work in all conditions as a clock. I use it for several years in a greenhouse as soon as it gets dark and the backlight. Simple as day! Look at the figure, this General scheme, about the way she looks. You will be able on the basis of such a scheme to build both simple and more complex device. To create a light barrier with a smaller number of parts simply will not work. Design of the day, it is simple and effective. Everything else, I want to add that the sensitivity of the device is quite high. The fact that the circuit has two transistors in the switching circuit as a single compound. This is used if you want to get a big gain on a current. In this case, did it. If a little clever, the switch transistors electronic band called "the Darlington circuit". Like I said earlier, all for the sake of increasing the coefficient for current gain, in this inclusion, indicators of each of the transistor multiplied. There is another significant advantage, this system has a large input resistance, this allows a wide range of sensors. See how the diagram is included photoresistor PR1. Now briefly about the scheme and how it works. The resistance of the sensor PR1 with growth irradiance drops in each scheme at least, in most cases it is several kilo ohms. If the night, then resistance becomes several Mega Ohms, and this is already enough, so that the transistor VT1 turned into "open". Track opens and VT2, which will trigger the relay K1, and its burden is already lighting circuit. Diode D1 is not particularly critical, but for the stability and damping of currents inductance desired. As you can see a small current in the sensor triggers the relay and the lighting. It is simple. The scheme is trimming resistance, it need to be rude to the sensitivity of the photo relay. It is placed in parallel to the resistor R1. To nourish such a scheme is possible from a simple power supply to 12V, the relay can use the corresponding relay, just select the operating current and voltage. The main thing to remember is that the transistor such that the switching circuit keeps the current through the relay is no more than 50mA, if more punches and the scheme is not working as expected:)) All success. Although, if you put the output transistor type CT 815, the current will be strong enough for the starter to 12V to turn on:)) Well it as you wish.