LDR based light controlled Home Automation system

LDR based light controlled Home Automation system

Introduction:

Automation is the thing we can see all around the globe in terms of advancement of this electronic era. We all know the first and foremost automation system anyone can be inspired of is home automation system, and the basic home automation can be a simple switch which can be controlled automatically with simple sensor like which we are using in this project. So, basically what we are doing in this project is that we are making a simple light controlled switch which can be turned ON automatically when there will be no light in the surrounding and automatically will turned OFF if there will be some lighting.

Here's the step by step process to make a DIY light controlled switch.

Components Required:

1. PCB Board
2. 12 V Relay
3. 4k Resistor
4. MOSFET 2N7000
5. LDR(Light Dependent Resistor)

CIRCUIT SETUP :

Setting up the LDR (+MOSFET) :

Here we have used MOSFET(2N7000) transistor for our circuit which will act as a switching circuit and for switching operation we have used LDR which is a light dependent resistor. LDR work as a resistor when there will be light on it and at that time it will have high resistance, but in dim light or no light it will act as short circuit or it's resistance gets down to low or just zero which is a short circuit situation. So, our purpose of turning the lights ON at night/low-light and turning them OFF when there is adequate surrounding light, is automatically fulfilled. 

MOSFET  as we all know that it can work as a switch as well as amplifier but here we are taking the operation of switch from this transistor. Here we had connected one more resistor of 4k.

Connection of Relay Module:

Here we have taken a 12 V relay of 5 pins. Relay make a separate connection of AC and DC on one circuit. It synchronises between AC mains and DC supply so that we can control the ac switch with dc voltage. As this relay is of 12V so if we give 12 v to the relay then it will be activated and it will make connection between common and normally open pin of relay(i.e. NO pin).

Note: The connection between the 220V AC device (or the bulb), and the 12V relay needs to be kept in mind. Otherwise, the relay may get permanently damaged, which is quite obvious as the relay can tolerate a max voltage of 12V DC voltage and 220 AC volts would burn it in a short instant. Instead, the relay simply acts as a switch for connecting the E1 Bulb's Common terminal to the Common/GND of the House supply. The circuit has been simplified to illustrate these points. Here, SW3 switch denotes the switching action performed by the LDR.

Final circuit setup:

So now here's our main or final step to connect all the components and find the result. We have connected the relay and the transistor as shown in the diagram. 

(All the lines/comments made with the BLUE sketch are not to be treated as wires/components e.g., the Coil Terminal of the relay)

After making the connection as shown in figure you need to connect the 12V power supply to the relay module so as to make the relay board  and circuit working.

Working of the whole Circuitry:

The aim of all this was to switch relays.In the other project (Home Automation using Bluetooth Module and Home Automation using IR remote),the Bluetooth module and the IR sensor were used to send the readings to the microcontroller, which was programmed and used to switch the relays using Arduino Uno. Here the Arduino is missing as we don't need it. 

So, at initial state, (suppose there is no light on our LDR and its Dark) the MOSFET has two of its terminals (Source and Gate) shorted. The +12V supply on the GATE terminal enables a channel for current to flow from the Source(connected to the positive terminal of the Relay) to the Drain (connected to the GND terminal of the Relay). The Relay module has now got a proper supply and gets activated. i.e., It disconnects the NC and COMMON and connects NO and COMMON. This further completes the circuit for the AC controlled terminal device (in our case, a BULB).  

In the other case, if there is sufficient light (due to the daytime light or any other source), the LDR exhibits very low resistance(rather Open Circuit). Hence, there is no connection between the Source and the Gate. So, the Gate does not get a +12V supply and is not able to generate channel between the Source and Collector. The Relay Module does not get activated and the Bulb stays disconnected. 

To summarize the logic:

No Light   ->   Short Circuit by LDR  -> Relay ON     ->   Bulb ON

   Light        ->   Open Circuit by LDR   -> Relay OFF   ->   Bulb OFF