8. INTRODUCTION:
Usually when a person enters the room in
darkness, we find it difficult to locate the wall-
mounted switch board to switch “on” the light.
For a stranger it is tougher still as he has no
knowledge of the correct switch to be turned on.
Here is our reliable circuit that takes over the
task of switching “on” and switching “off” the light
automatically when somebody enters or leaves
the room during darkness. The circuit has
following salient features:
9. It turns “on” the room light whenever a
person enters the room, provided that the
room light is insufficient. If more than one
person enters the room, say, one after the
other, the light remains “ON”.
The light turns “OFF” only when the
room is vacant (or) in other words, when
all the persons who entered the room have
left.
10. BLOCK DIAGRAM DESCRIPTION:
1. POWER SUPPLY UNIT:
Power Supply Unit provides DC supply to ICs and components.
STEP DOWN
TRANSFORMER
0V-09V
RECTIFIER
DIODE
FILTER
CAPACITOR
VOLTAGE
REGULATOR
IC 7805
230V, 50Hz 5V, 500mA
AC Mains Constant DC
09VAC Pulsating DC Pure DC
(Removes Ripples)
11. TRANSFORMER:-
Here are using step down transformer to reduce the voltage level.
RECTIFIER:-
A bridge wave rectifier converts an AC input voltage to a pulsating DC.
The pulsating DC voltage is only suitable to be used as a DC power supply.
FILTER:-
A circuit uses to reduce the fluctuations in the rectified output voltage are
ripple. This provides a steadier DC voltage regulator
REGULATOR:-
A circuit uses to produce a constant DC output voltage by reducing the ripple
to negligible amount.
12. The 9 volts transformer is given as the input to the 7805 IC
provided with rectifier and filter circuit. Apart from the IC drop(2.4v), we
have to consider the drop across all the components. So in order to get
5v output, the minimum voltage for the IC is 9v. By using an 7805 IC 5v
dc can be given to the basic IC’s, and 5v dc is used to drive the relay.
TR1
TRAN-2P2S
D1
DIODE
D2
DIODE
D3
DIODE
D4
DIODE
C1
1000u
VI
1
VO
3
GND
2
U1
7805
R1
25
Volts
+4.99
TR1(P1)
14. TRANSMITTER:-
Here we are using IR transmitter using Astable multivibrator. It is a free
running multivibrator that has no stable states but switches continually between
two states this action produce a train of square wave pulses at a fixed frequency
PHOTO DIODE:-
A photo diode is a transducer that takes light energy and converts into
electrical energy.
DIFFERENTIATOR:-
A differentiator is a ckt that is designed such the output of the ckt is
approximately directly proportional to the rate of change of input
15. MONOSTABLE MULTIVIBRATOR:-
A one-shot multivibrator that has one stable state and is
triggered externally with it retuning back to its first stable state.
UP/DOWN COUNTER:-
It is also known as bidirectional counters. Both synchronous and asynchronous
counters are capable of counting up/down count but there is another more
universal type of counter that can count in both directions either up/down
depending on the state of their input control pin and this are known as
bidirectional counters.
DISPLAY:-
It will display the up/down counts.
16. CONTROL ELEMENT:-
It will control the relay as per the up/down counter out. When the up/down
counter is “0” only the relay get switch off
RELAY:-
Relay is a electro mechanical switch.
28. DETAILED CIRCUIT
DESCRIPTION
The IR transmitter circuit consist
of an astable multivibrator NE555
timer IC1.
The output of IC1 at pin 3 is a
unregular square waveform. This
output is used to drive IR LED, which
transmit IR light.
Modulated frequency is used
because the IR receiver modules
used in this circuit respond to IR
signal modulated frequency.
29. We are not considering Modulating frequency
because we are using photo diode.
so we are using constant resistance.
Resistor R3is a current limiting resistor that keeps
the IR LEDs, current within the required range.
30. PHOTO DIODE
The Photo diode have two terminals for Vcc (Anode)
(+5v), ground(cathode). In the normal state.
It receive light from the IR transmitter and it will act
like a closed switch.
So the entire voltage will go to the ground
Whenever the object (or) obstacle come between
the IR transmitter and Photo diode at the time Photo
diode will act as a open switch
The entire voltage will go to inverting terminal of op-
amp
31. COMPARATOR
Op-amp will act as a
comparator.
Whenever the Photo diode will
act as a open switch The voltage
at inverting is equal to the
voltage at non inverting so the
comparator will produce low
output. And it is given to the
monostable multivibrator
D2
LED
R4
10K
R5
10K
R6
10k
R7
10K
3
2
6
74
81
U2
OP07
R8
33K
C4
100p
32. When ever the Photo diode will act as a closed
switch the voltage will go to the ground and some
reference voltage will appear across non-
inverting terminal and no voltage will appear
across inverting terminal of the op-amp.
Whenever the obstruct is coming between IR
transmitter and receiver the Photo diode will act
as a open switch So the output of differentiator
will produce low output. And it will give input to
the monostable multivibrator
33. In the circuit, two NE555 timer ICs (IC1 and IC2)wired
as monostable multivibrators are used. The pulse width of
the output waveforms (ON time) for these multi vibrators is
fixed at about 3.3 seconds by suitably selecting the values
for the timing capacitors c5 and c6 in conjunction with
their associated resistors R8 and R9.
MONOSTABLE MULTIVIBRATOR
R
4
DC
7
Q
3
GND
1
VCC
8
TR
2
TH
6
CV
5
U3
555
C5
0.1uf
C6
30uf
R9
100k
1 2
U4:A
7404
i/p
O/p
34. These monostable multivibrators get triggered
when their trigger input pins (pin 2) goes low. Thus
the multivibrators are triggered only when the IR
light beams are interrupted. Although the output
pulse width of both the multivibrators are
approximately the same.
When the object coming between the IR link
the i/p of the monostable is low so the o/p of the
monostable is high so o/p is connected to the not
gate and it given to the up/down counter
35. UP/DOWN COUNTER
o counter 74LS192 IC are used to counting the up
and down count.
o Monostable output is given to the 4th pin of
74192. It will do DOWN count.
o When ever the monostable output is given to the
5th pin 74192.It will do UP count.
o The IC output of Q1,Q2,Q3,Q4 is connected to
the driver IC(7447). And it will also connected to the
4 diodes.
o The 4 diodes output is connect to the base
terminal of the transistor.
36. o And the transistor emitter is connected to the
ground and collector is connected to Vcc.
o whenever the voltage present at the base
terminal the voltage will go to the ground.
o So the Relay will get switch ON. So light will not
glow
o Whenever the no voltage present at the base
terminal so the transistor will not switch on.
o So the relay will get switch off And the light will
not glow
37. DISPLAY
• Counter IC output is given to the input of the driver IC
(7447).
• 7 segment display is a most popular display device
used in digital system for displaying data using this device.
38. • The data have to converted from BCD to SSD code
• The IC 7447 decoder are driver has 4 input lines,7
output lines to drive a SSD
• Active low output terminal a bar through g bar of
decoder or connected to a through g terminals of display
respectively
• Has output of decoder or active low ,SSD LED’s of
common anode types used.
39. ADVANTAGES
39
The light will not glow if no person is present
inside the room.
The light will on only when the person enters the
room .
Displays the number of persons present inside the
room.
40. The circuit requires different path for both entrance
and exit way for the proper way of working.
DISADVANTAGES
41. LIMITATIONS
41
It can’t display more than 9 (no: of persons)
,as the circuit is not cascaded.
As we had used the decade counter, when
the 10th person gets in, the light automatically
goes OFF.
