The classroom has the most varrying number of vistors within a day, than most other common places. Also, it is one the most significant place the number of people inside the class is significant. Being a place of learning, the time spent by the teacher inside is valuable and hence, attendance is definitely a place where time can be saved.
Another angle to this situation is the energy consumption. Most students are seemingly oblivious to the actual energy needed to the energy they consume. Hence, a lot of energy is wasted. In this scenario, the need of the day is an automated system which will monitor the number of students inside the class and also act as an intelligent system that will control the actual number of energy consuming devices being used.
With this in mind we have designed a system which will do exactly the same. The aim of the system is “classroom automation and energy saving unit”. As a result a two sensor are used to minitor the number people entering the classroom. & leaving the classroom & shows it on two different seven segments This will be used to calculate the number of people inside the classroom. The Controller is the device which decides how many lights should be ON and which should remain Off.
Although the system was intended to be universal, a few assumption in the design had to be made. These consideration, though not very limiting in its scope, do put a few restrictions on the area of the operation. Design has been based taking into account the fewest number of assumptions and exception. These considerations if violated, do not hamper the working of the sytem, but do put a dent in its reliability. Hence, it is recommended that these considerations are followed.
The considerations were taken while designing the system:
1) The entry and exit doorways are different
2) The Doorway width does not exceed 1.5m, and has enough space for mounting.
3) The doorway has no exposure to any strong “DC” light, or flashes.
4) The microcontroller has constant, uninterrupted supply and reset only when none are inside the class.
5) People that can be inside the class at a time are less than 9 persons.
6) Entry and exit time are not more than 500ms.
1) The Senor consists of a pair of IR Transmitter-Receiver pair.
2) The sensors indicate a high pulse every time an obstruction appears in between the transmitter receiver’s line of sight.
3) The signal conditioning circuit consists of a Low-pass filter and a comparator. This circuit removes any fluctuation in sensor output and brings its output to the proper level to interface it with the microcontroller.
4) The Microcontroller continuously polls the input terminals of both the sensors. Depending upon the sequence of sensor outputs, the microcontroller decides whether a person walked inside or out.
5) The Microcontroller keeps a count of the number of people inside the room depending upon the sensor outputs. This value is shown on an LCD or seven segment display.
6) The microcontroller is also connected to relay which control the lights inside the classroom. Depending upon the number of people inside the classroom, the relays control the number of lights.
The entire system runs on a included power source and is isolated from high voltage AC by the relay
(1) IR TRANSMITTER:
The IR transmitter used was designed with respect to the IR receiver used. Since, the IR Receiver used was TSOP 1738, the IR transmitter needed to capable of giving its output in the burst mode. The burst mode consists of the pulsating input signal of 38KHz and a modulated by another such that the ‘ON’ time becomes more than 14 cycles while the ‘OFF’ time becomes more than 20 cycles.
Multivibrator 1 gives a square wave output of 38KHz. So its duty cycle is 65%(because of burst mode) with an ‘ON’ time as,
T = 1 ÷ 38000 =26.31µs
Same for both IR transmission circuitFor obtaining the above outputs, we need the following components:
R1’ =11.3kΩ R1 = 11.3kΩ
R2’ = 13.3kΩ R2 = 13.3kΩ
C1 = 1nF C1’ = 1nF
(2) IR RECEIVER:
The Receiver used is TSOP 1738, manufactured my Vishay Siliconix. The receiver is a IR receiver which works in two modes, namely the Continious mode and Burst mode.The Continious mode operation is intended for small range use and restricts to only a few inches. The burst mode operation however is intended for long range use. If the transmitter power is high enough, the range is upto a couple of meters.
Specifications of the receiver are:
-0.3V to 6V
-0.3V to 6V
The Receiver has a photodetector and preamplifier within the same package. The total signal conditioning and fallback features are implemented within the same package. The package consists of a PCM filter. The receiver has high ambient light immunity.
The receiver has and Automatic Gain Control (AGC) unit within it. This unit reduces the gain of the receiver once a continious signal is received, it reduces its gain to avoid false detection due to ambient light.
The receiver output is TTL/CMOS compatible.
The output is a square wave of frequency 3KHz (approximately) of amplitude 122 Vp-p'> with an offset of 3V, when there is no obstruction. Hence, the output wave swings from 3V to 5V. The output becomes a constant 5V DC when there is an obstruction.
(3) SIGNAL CONDITIONING:
The output of the receiver, although TTL compatible, it is difficult to process. Also, if direct processing were to be done, it would take valuable polling time. Hence, an intermediate Monostable Multivibrator using IC555 is added so that the output is easier to process.
The ‘no obstruction’ ouput is a square wave of 3V minimum value, and with a frequency of 38KHz. This output is given to the trigger input of an Monostable multivibrator. When the sensor output is a square wave, the negative going edges of the square wave triggers the multivibrator gives a square pulse. The 38KHz input continiously triggers the multivibrator and the output remains at 5V. When the sensor ouput is a constant DC 5V, the multivibrator isn’t triggered at all, and gives an output of DC 3V. This gives us the final output as,
OBSTRUCTION – DC voltage of 5V
NO OBSTRUCTION – DC vtg of 1.3V
The microcontroller used is Intel 8952 architechture microcontroller. The one being used is Atmel AT89S52. The AT89S52 provides the following standard features: 8K bytes of Flash,
256 bytes of RAM,
32 I/O lines,
two data pointers,
three 16-bit timer/counters,
a six-vector two-level interrupt architecture,
a full duplex serial port,
and clock circuitry.
In addition, the AT89S52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes.
The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning.
The Power-down mode saves the RAM con-tents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset..
The chip was chosen such that it has the least onchip memory, since the processing isn’t demanding of memory.
The program was burnt into the chip using external programmer device and the Embedded Development Tools software was used. The code was compiled using the Crossware Compiler.
(5) SEVEN SEGMENT DISPLAY
The SEVEN SEGMENT display is the last stage of the system and is the final output. The SEVEN SEGMENT also has the useful feature of auto refreshing.(by programe).here since single seven segment is used for incoming counter & single segment is used for outgoing counter…since max. count limit is 9 persons..
The relay may be considered as the final effect of the system. There is one relay, It is connected to Lamp loads. The lamps represents the actual AC device to be run. The ‘Normally open’ (Off) conacts are used as trigger inputs for the relay. Once triggered, the ON switches will toggle to closed, and the Lamp loads will be switched ON. The lamps remain ON till the relay trigger is given, and turns off when the trigger is removed.
(here we can also control the no of lights in room depending upon the no of persons inside the class)
1) As the name suggest it is a model of INTELLIGENT CLASSROOM so it is useful to make very scientific classroom
2) It can be used as the person counter purpose as concern as attendance of students.
3) Here it is also used for power saving purpose…because using relay we are controlling the lights of the room & also other power equipment
4) It’s also usefull to count the strength of the persons inside the room
5) It project can be developed with making password enable incoming & outgoing door…
6) It can be used with some extra features in offices , malls, auditoriums & highly restricted area….or self controlling area..as automatic system..
Initially the hardware was not responding as we had expected it to. This was due to certain physical aspects and design anomalies we did not consider. These were:
1) TRANSMITTER did not respond to mode 1 (continious) transmission. This was because the transmitter IR LEDs were not transmitting with full capacity. The receiver would recognize this as DC noise and reject it. Hence, the receiver did not respond to the tranmitter.
So this problem can be solved by changing the transmitter to operate of mode 1 (burst) tranmission.
Also, we replaced the existing LEDs with higher candescence LEDs. Both these changes made the difference and the receiver started responding to the transmitter.
2) SIGNAL CONDITIONING used before consisted of a lowpass filter and comparator. However, the LPF capacitor stored the charge much longer than expected, and hence, a DC output vtg. Couldn’t be recognized till it discharged.
We solved this problem by, replacing the LPF+Comparator bloack by a Monostable Multivibrator.