08-11-2012, 11:50 AM
AUTOMATIC CONTROL OF EQUIPMENTS IN A ROOM WITH TEMPERATURE CONTROLLED FANS
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INTRODUCTION
The project title is “AUTOMATIC CONTROL OF EQUIPMENTS IN A ROOM WITH TEMPERATURE CONTROLLED FANS.”
In today‟s world, there is a continuous need for automatic appliances with the increase in standard of living; there is a sense of urgency for developing circuits that would ease the complexity of life. Many times we forget to switch off appliances like lights, fans and air conditioners before leaving house, office, college etc. This leads to considerable wastage of electricity apart from reducing the life of appliance.
The circuit presented here senses the absence of occupants in a room and automatically shuts off the power to a particular appliance, say a tube light or fan. It turns on the appliance again when someone enters the room. The circuit uses LDRs as sensors.
Along with the automatic room controller circuit, an extra circuit is provided for automatic temperature controlled fan. Here the speed of the fan can be linearly controlled, depending on the room temperature. The circuit use LM35 as the temperature sensor and is highly efficient.
The objective of this project is to make a controller based model to count number of persons visiting particular room and accordingly light up the room. Here we can use sensor and can know present number of persons.
Power Supply:-
Here we used +12V and +5V dc power supply. The main function of this block is to provide the required amount of voltage to essential circuits. +12V is given to relay driver. To get the +5V dc power supply we have used here IC 7805, which provides the +5V dc regulated power supply.
Enter and Exit Sensors:-
This is one of the main parts of our project. The main intention of this block is to sense the person. For sensing the person and light we are using the light dependent resistor (LDR). By using this sensor and its related circuit diagram we can count the persons.
Temperature sensor:-
Temperature sensor is one of the two sensors used in our project. The function of this is to sense the surrounding temperature and to produce an output voltage corresponding to it. Here we are using LM35 as the temperature sensor. By using the output of the sensor, we can control the speed of the fan.
16F877A:-
It is a low power, CMOS 40 pin micro controller having very versatile applications. It consists of program memory, read only memory(ROM) and electrically erasable programmable read only memory(EEPROM).It consists of timers, analog comparator, counter etc. , with 35 instructions that are generally single cycle instructions except for program branches which are two cycle.
Relay Driver Circuit:-
This block has the potential to drive the various controlled devices. In this block mainly we are using the transistor and the relays. One relay driver circuit we are using to control the speed of the fan. Output signal from 16F877A is given to the base of the transistor, which we are further energizing the particular relay. Because of this appropriate device is selected and it do its allotted function.
Automatic room control circuit
The 230V supply is step down to 12V ac using a 12-0-12 transformer which is then converted to a 12V dc using a bridge rectifier. Capacitor is provided to filter the ripples present in the 12V dc output. This filtered 12V dc is regulated to a 5V dc which is then fed as VCC to components like PIC, LM35, LDR-LED combination ,seven segment display etc. The relays are fed with 12V dc.
The input voltage given to the LDR-LED combination give raise to a current to flow through the circuit. The combination being a voltage divider circuit, the current gets divided into two, let i1 be flowing through LDR 1 and i2 be flowing through LDR2.The LDRs are constantly supplied with light from an LED or LASER diode which will give resistance minimum due to which the current i1 will drain out to the ground. But when someone enters or leaves the room the light falling on the LDR 1 gets blocked first as a result the current i1 will select a less resistance path, which will lead to the PIC. Then the light falling of the LDR2 is blocked and the same process repeats. The outputs from the LDRs are in analog form, which should be converted to a digital signal. Hence the outputs from the LDRs are fed to the ADC pins of the PIC. According to this signal, the LED-1 or LED-2 will glow to represent the entry or leaving of a person. When someone enters the room, the value of the decade counter of the PIC is incremented by one, and when someone leaves the room, the value of the counter is decremented. The count is displayed using a seven segment display or LEDs. The output from the PIC is fed to Relays.
Temperature control circuit
The major part of the circuit is the temperature sensor, LM35, which is a highly efficient one. The analog output of the temperature sensor is converted to digital signal by the ADC part in the PIC. The sensor senses the surrounding temperature.
A reference temperature of 25°C is stored in the PIC. The fan will be switched on, only if the surrounding temperature is greater than the reference temperature. If the difference between the temperatures is very small, and then the relay 1 is switched on, which will connect a large resistance R1, in series to the fan circuit. And the fan rotates in minimum speed. As the difference in temperature increases, the Relay 2 is switched ON, which will connect the resistor R2, such that, R2<R1 in series with the fan and the fan rotates in an increased speed. And if the temperature difference is further increased, the Relay-3 gets switched ON, which will connect the resistor R3 in series with the fan, such that R3<R2<R1 and the speed further increases and if the temperature difference is maximum, the Relay-4 is switched on, which will connect the minimum resistance R4 to the fan, and thus the fan rotates with maximum speed.
CONCLUSION
We here by conclude our project with the confidence that by implementing our project in houses, libraries, public halls etc. we can minimize power wastage to a great extent. As part of the project we have successfully imparted LDRs and LM35 to ensure power savings through automated switching of power by detecting human presence in the room or space considered.
Through this project we have achieved a system which is of low cost, user friendly, a system that can be implemented on a single door, which reduce the wastage of power, which reduces the human efforts. Here we have achieved whatever we require, and have made this project an impressive and economic one by abiding to standard methods.