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Automated Outdoor Lighting

This Project enables a person to make any Outdoor Lighting Automated i.e to switch On/Off according to the sunlight outside. If it is dark outside then the light will turn On and if it is daytime then it will automatically switch Off. This can be very useful for all Outdoor Lighting of various commercial buildings as well as for residential buildings. This can also be implemented in Vehicles which will automatically turn their lights On. Our aim can be achieved by designing a proper transistor circuit and using a relay with it to control the high voltage network. The Requirements Are:

 1:- Bipolar Transistor(Bc 547)
2:-5/6v Spdt Relay
3:-Resistors(Around 4.5k And 3k Ohm)
4:-Light Dependent Resistor
5:-5v Power Supply
6:-Pcb For Soldering Things Together
7:-Multimeter





  •         CIRCUIT AND EXPLANATION


The project involves the use of a transistor as a switch to make the outdoor light on/off. As we know that transistor can be used in three different regions of operation namely saturation, active and cutoff region. These regions can be known from the datasheet for the transistor used.
            
                   
For switching, the transistor must work only in saturation and cutoff region. So our first objective is to design a circuit which makes the transistor to work in saturation/on state when the light is there and to go into cutoff/off state when there is no light. Now as we know the LDR changes its resistance according to the light. If there is more light its resistance decreases and if there is dark, then its resistance increases. So we need to know the resistance of LDR in above two states and hence we use a multimeter and take the two resistances in darkness and in the light. In my case, it was around 3k in light and around 800k in darkness. So now we design a circuit which changes the state of the transistor according to the change in resistance of LDR. Now with a bit of knowledge about transistor and its biasing, we get to know about the values of two resistances r2 and r3.in first case taking resistance of LDR as 3k ohm, we make  r3 to be 3k as to build a simple voltage divider. The value of r2 is to be determined as to make the transistor work in the saturation region. For saturation state, we need to keep the base terminal current as high as possible so that collector terminal current may increase to its saturation value. We know from the datasheet we need to keep base current above 300-350 microampere for saturation region. So taking the value of base current as 300-350 uA and applying Kirchoff's law in the base-emitter loop, r2 comes around 4.5k.

So now the transistor works in saturation mode and hence the voltage across the collector-emitter terminal is approx. Equal to the applied voltage as the transistor works as a short circuit. Now we need to connect the 5 v power supply across the collector-emitter terminal and also a relay in b/w. When the LDR changes to 800k then it works almost as an open circuit and hence base is not biased so the transistor is cut off, so the relay is also off.




The connections are to be made like above. Any simple adapter can be used to provide 5v or above. This circuit can be assembled on a PCB and can be covered with a transparent sheet so that only light enters.                                                                     
It should look something like this on a breadboard.



Now we need to assemble all the components on PCB.


Now the relay is to be connected to the high voltage line. It must be noted that there are 2 options for the relay and we have to make sure that the connection is short circuited when the relay is off and open when the relay is on.

So now the circuit is complete and we need to power on the adapter.


Hence the automated outdoor lighting is complete.
To demonstrate the working, a short video is attached below.

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