Home Automation Lighting Control
Created: Feb 26, 2015
No description available.
This device is a home automation lighting solution based on the presence of a person inside the room. When a person enters or leaves the room, the circuit automatically turns the lights of a room ON and OFF respectively. It also has a memory element which eliminates undesired switching of the lights in the event of more than one person entering or leaving the room.
The circuit uses two Light Dependent Resistors (LDR) which are placed on different locations and separated by a considerable distance (say one meter) to independently sense a person entering and leaving the room. The outputs of the LDRs are applied to two counters; the first counter will count as +1, +2, +3 and so on when persons enter the room, on the other hand, the second counter will count as -1, -2, -3 and so on when persons leave the room. The type of counters used are Johnson Decade Counter ICs, part number 74HC4017BQ. The outputs of the LDRs are also coupled to LEDs which emit green and red lights when a person enters or leaves the room. The next stage is comprised of two logic ICs which combine the output of the two timers and determine if there is any person left in the room. The logic ICs are in a single package of the 74ABT08D Quad 2-input AND gate. The output of the gates are then fed to a NPN Bipolar Junction Transistor (BJT) which regulates the current to the relay which will energize the lights. The relay closes or opens depending on the current from the transistor.
Once triggered ON, the bulb remains ON until all persons who entered the room have left. The maximum number of persons that this circuit can handle is limited to four because after the receipt of the fifth clock pulse, the counters are reset. The capacity of the circuit can be easily extended to handle up to nine persons by removing the connection of pin-1 from the reset pin-15 and utilizing Q1 to Q9 outputs of CD4017BQ counters, however, additional inverters, AND gates, and diodes will be required.
Automation of room lights is one of the applications of this circuit, but devices such as air conditioning units, television, and other home or office appliances may also be automated by adjusting the relay and power requirements. Homes, offices, and establishments such as hotels may also take advantage of this technology.