SHADOW
DETECTOR
K. SATHYAPRAKASH
RAO
BROAD
AREA
This simple project is based on basic electronics
leading to the development of a module or an instrument which can be used in
various applications.
A physical module/instrument is developed which can
be used in any surroundings. The working
can be seen by adjusting the circuit according to the surroundings.
ABSTRACT
This is the
circuit of a simple burglar alarm that produces a loud beep when
somebody crosses a protected area or door. The circuit is highly sensitive and can detect
the shadow of the moving person from a distance of 1 meter. It does not require an aligned light beam to
make the circuit standby. It is portable and can be placed anywhere for
monitoring.
IC1 is
designed as a voltage comparator. Its non inverting input is connected
to a potential divider R1 and VR. By adjusting VR, input current to pin3 can be
set to a reference level. The inverting input of IC1 is connected to a photo
diode. IC CA3130 is a 15 MHz BiMOS Operational amplifier with MOSFET
inputs and bipolar output. The inputs contain MOSFET transistors to provide
very high input impedance and very low input current as low as 10pA. It has
high speed of performance and suitable for low input current applications.
CA3130A
and CA3130 are op amps that combine the advantage of both CMOS and bipolar
transistors. Gate-protected P-Channel MOSFET (PMOS) transistors are used in the
input circuit to provide very-high-input impedance, very-low-input current and
exceptional speed performance. The use of PMOS transistors in the input stage
results in common-mode input-voltage capability down to 0.5V below the
negative-supply terminal, an important attribute in single-supply applications.
A CMOS
transistor-pair, capable of swinging the output voltage to within 10mV of
either supply-voltage terminal (at very high values of load impedance), is
employed as the output circuit.
The CA3130 Series circuits operate at supply voltages ranging from 5V to
16V, they can be phase compensated with a single external capacitor, and have
terminals for adjustment of offset voltage for application requiring
offset-null capability. Terminal provisions are also made to permit storing of
the output stage. The CA3130A offers superior input characteristics over those
of the CA3130.
AREAS
OF APPLICATION
The circuit is an effective instrument with
electronic output. Hence the output can be used for any applications. A few effective
applications are
1. It
can be used in bank and vault, for very high and sensitive security.
2. It
can be used in prison, home for total lock down. Anyone trying to break through
can be sensed by placing the device in a suitable place.
3. It
can be used as a sensor device to identify any kind of movement.
CIRCUIT
DIAGRAM
The circuit uses
the light sensing property of the PIN
Photodiode. The p-n junction of the photo diode gives light current when
it is forward biased.
OP AMP’s non
inverting input is connected to a potential divider R1 and VR. By adjusting VR,
input current to pin3 can be set to a reference level. This VR can be set to
any kind of light ranging from low intensity to high intensity.
Inverting input
of OP AMP is connected to a photo diode.
Normally in the
light (as set by VR) Photodiode gives voltage to pin2 of OP AMP.
Since this
voltage is higher than the voltage set by VR at pin3, output of OP AMP remains
low keeping LED and buzzer off.
When a person
approaches the photodiode, the shadow causes a reduction in current through the
photodiode so that voltage at pin2 decreases below that of pin3. Output of OP
AMP then goes high and Buzzer sounds.
PHOTOGRAPHS
FIG1:
CIRCUIT UNDER TUBELIGHT
FIG2:
CIRCIUT RESPONDING TO SHADOW UNDER TUBELIGHT
FIG3:
CIRCUIT IN SUNLIGHT
FIG4:
SHADOW APPROACHING THE CIRCUIT
FIG5: CIRCUIT
RESPONDING TO SHADOW UNDER SUNLIGHT
RESULTS
AND DISCUSSIONS
Hence a circuit which is simple, cheap, efficient
and sensitive is developed. The working and the response is clearly depicted in
the photographs above. Similar to the response under normal tube light and
sunlight, the circuit can be adjusted to any kind of light by varying the VR.
Even in cloudy days and night times the circuit can be adjust by focusing small
amount of light on the circuit or by adjusting it to the light present. The
photodiode detects the changes in the available light and the circuit will definitely
respond.
ADVANTAGES
•
99% the circuit respond to every
possible lighting situation. There cannot be a situation where the circuit will
not work.
•
That is, it works with minimum light and
also with maximum light.
•
Sensitivity of the circuit increases with
increase in surrounding light.
NOTE
•
The
circuit triggers when the light intensity changes without a shadow. It is
better to keep the unit in a place where constant light is available
•
That
is, when light in the surroundings changes photodiode responds to it and buzzer
goes on. So it is necessary to adjust the VR according to the surrounding light
