In many places like classrooms, offices, and small halls, fans and air conditioners are often left ON even when there are no people inside. This leads to unnecessary power consumption and higher electricity bills. Also, manually switching devices ON/OFF every time someone enters or leaves is not efficient. So, there is a need for an automatic system that can control fan and AC based on the number of people present in the room.
Schematic:
The system consists of two IR sensors placed at the
entry and exit door. These sensors are connected to a PLC. The PLC is also
connected to output devices like a fan and an air conditioner through relays or
contractors. A display unit can also be connected to show the number of
visitors inside the room.
LADDER DIAGRAM:
Solution:
The solution is to design a PLC-based visitor counter
system. When a person enters, the entry
sensor detects and increments the count. When a person leaves, the exit
sensor detects and decrements the count. If the count is greater than
zero, the PLC will turn ON the fan. If the count increases beyond a certain
number (for example, more than 3 people), the
AC will also turn ON. When the count becomes zero, both fan and AC will
turn OFF automatically.
PLC Program (Ladder
Diagram Description):
-
Use two inputs: I0.0 for Entry Sensor and I0.1 for Exit Sensor
-
Use one counter
for counting number
of persons
- Increment counter on I0.0 signal
-
Decrement counter on I0.1 signal
-
If counter value > 0, turn ON output Q0.0 (Fan)
- If counter
value > 3, turn ON output Q0.1 (AC)
- If counter
value = 0, turn OFF both
outputs
Explanation:
In this system, PLC plays the main role in controlling
the entire operation. The IR sensors detect movement and send signals to the
PLC. Based on these signals, the PLC program updates the count value using up
and down counting logic. This count is then used as a condition to control output.
When at least one person is inside the room, the fan is
automatically turned ON to provide ventilation. When more people are present,
the temperature may rise, so the AC is also turned ON for better comfort. When
all people leave, the system automatically turns OFF all devices, saving
energy.
This system is very useful in real-life applications
like classrooms, meeting rooms, and offices. It reduces human effort, saves
electricity, and increases efficiency. The project also helps in understanding
PLC programming, sensors, and automation concepts in a practical way.