35420164-Shadow-Alarm.doc (Size: 633.5 KB / Downloads: 154)
Our mini-project is to design and check the functionality of ‘SHADOW ALARM’ circuit . Shadow Alarm is opto-sensitive circuit that sounds an alarm whenever a shadow falls on it .Now a days it is widely used in aspects of security systems ,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 good for home-security too. A dim lighting in the room is necessary to detect the moving shadow. Unlike opto-interruption alarms based on light-dependent resistors (LDRs), it does not require an aligned light beam to illuminate the photo-sensor.
This opto-sensitive circuit sounds an alarm whenever a shadow falls on it. So it can be used at night by shopkeepers to protect the valuables in their showrooms. A dim light in the room is necessary to detect the moving shadow. Unlike opto interruption alarms based on light-dependent resistors (LDRs), it does not require an aligned light beam to illuminate the photo-sensor.
The circuit is powered by a 9V PP3 battery and uses the most sensitive photo-sensor L14F1 to detect shadows. It is portable and can be used at any place that is to be monitored. Op-amp μA741 (IC1) is used as a voltage comparator. Its inverting input is biased by the voltage obtained from the junction of 100k resistor R1 and the collector of phototransistor T1. The non-inverting input of IC1 gets a controlled voltage from potential divider R2 and VR1.
IC 7555 PIN DIAGRAM
The ICM7555 is a CMOS timer providing significantly improved performance over the standard NE/SE555 timer, while at the same time being a direct replacement for those devices in most applications. The ICM7555 is a stable controller capable of producing accurate time delays or frequencies.
In this mode of operation, the timer functions as a one-shot.See Figure 3. Initially the external capacitor © is held discharged by a transistor inside the timer. Upon application of a negative TRIGGER pulse to pin 2, the internal flip-flop is set which releases the short circuit across the external capacitor and drives the OUTPUT high. The voltage across the capacitor now increases exponentially with a time constant t = RAC.When the voltage across the capacitor equals 2/3 V+, the comparator resets the flip-flop, which in turn discharges the capacitor rapidly and also drives the OUTPUT to its low state.TRIGGER must return to a high state before the OUTPUT can
return to a low state.