25-03-2011, 11:32 AM
making of shadow alarm pcb
25-03-2011, 11:32 AM
making of shadow alarm pcb
18-07-2012, 01:37 PM
SHADOW ALARM a SHADOW ALARM.doc (Size: 1.89 MB / Downloads: 72) ABSTRACT This shadow alarm switch can sense a moving shadow in confined area. This project we can use in two ways. It can be used to protect things from theft when it is used as an alarm, means when somebody approaches the unit, it will give a sound alarm to abort the attempt of theft. It can be used as a switch when some body are applying technology, which has recently attracted attention in the field of power system protection and control system on ahead of the industry field. We have developed a circuit which can reduce the total cost of maintenance and management of protection and control equipment. At present, a Remote Operating and Monitoring System for protection and control equipment has been verified for real use and put into service in order to maintain this system it is very difficult and expensive. The circuit that we develop is very simple to make and less expensive, here the disadvantage is that it requires light in order to sense the shadow overcome by using photo diode. INTRODUCTION Shadow Alarm is opto-sensitive circuit that sounds an alarm whenever a shadow falls on it. When somebody approaches the unit, it will give a loud alarm to abort the attempt of theft. Now a days it is widely used in aspects of security system, where security is our main concern .So it can be used at night by shopkeepers to protect the valuables in their showrooms. It can also be used to provide security at warehouses (go-downs) where storage and protection of various types of goods is main concern, and works well for home-security too. Lighting in the room is necessary to detect the moving shadow. The circuit uses the light sensing property of the Photo resistor. This gives change of voltage when light falls on it. IC1 is designed as a voltage comparator. A variable resistor is used to balance the bridge. According to the voltage changes, the output will change automatically. IC 741 DESCRIPTIONS The Operational Amplifier is probably the most versatile Integrated Circuit available. It is very cheap especially keeping in mind the fact that it contains several hundred components. The most common Op-Amp is the 741 and it is used in many circuits. An Operational Amplifier ("op-amp") is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. An op-amp produces an output voltage that is typically hundreds of thousands times larger than the voltage difference between its input terminals. Operational Amplifier is important building blocks for a wide range of electronic circuits. They had their origins in analog computers where they were used in many linear, non-linear and frequency-dependent circuits. Their popularity in circuit design largely stems from the fact that characteristics of the final op-amp circuits with negative feedback (such as their gain) are set by external components with little dependence on temperature changes and manufacturing variations in the op-amp itself. Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid Operational Amplifier with special performance specifications may cost over $100 US in small quantities. Op-amps may be packaged as components, or used as elements of more complex integrated circuits. Differential amplifier It is implemented by two cascaded stages satisfying the conflicting requirements. The first stage consists of the NPN-based input emitter followers Q1 and Q2 that provide high input impedance. The next is the PNP-based common base pair Q3 and Q4 that eliminates the undesired Miller effect, shifts the voltage level downwards and provides a sufficient voltage gain to drive the next class A amplifier. The PNP transistors also help to increase the reverse Vbe rating (the base-emitter junctions of the NPN transistors Q1 and Q2 break down at around 7 V but the PNP transistors Q3 and Q4 have breakdown voltages around 50 V). Biasing circuit The classical emitter-coupled differential stage is biased from the side of the emitters by connecting a constant current source to them. The series negative feedback (the emitter degeneration) makes the transistors act as voltage stabilizers; it forces them to adjust their VBE voltages so that to pass the current through their collector-emitter junctions. As a result, the quiescent current is β-independent. Here, the Q3/Q4 emitters are already used as inputs. Their collectors are separated and cannot be used as inputs for the quiescent current source since they behave as current sources. So, the quiescent current can be set only from the side of the bases by connecting a constant current source to them. To make it not depend on β as above, a negative but parallel feedback is used. For this purpose, the total quiescent current is mirrored by Q8-Q9 current mirror and the negative feedback is taken from the Q9 collector. Now it makes the transistors Q1-Q4 adjust their VBE voltages so that to pass the desired quiescent current. The effect is the same as at the classical emitter-coupled pair - the quiescent current is β-independent. It is interesting fact that "to the extent that all PNP βs match, this clever circuit generates just the right β-dependent base current to produce a β-independent collector current". The biasing base currents are usually provided only by the negative power supply; they should come from the ground and enter the bases. But to ensure maximum high input impedances, the biasing loops are not internally closed between the base and ground; it is expected they will be closed externally by the input sources. So, the sources have to be galvanic (DC) to ensure paths for the biasing currents and low resistive enough (tens or hundreds kilohms) to not create significant voltage drops across them. Otherwise, additional DC elements should be connected between the bases and the ground (or the positive power supply). |
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