SHADOW DETECTOR

K. SATHYAPRAKASH RAO

B.E. EIE FINAL YEAR

11099G019

SCSVMV UNIVERSITY

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

WORKING PRINCIPLE

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