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10-09-2015, 01:36 PM

Please send the Shadow alarm full document

jaseela123d · 15-03-2017, 11:57 AM

This opto-sensitive circuit sounds an alarm whenever a shadow falls on it. So it can be used at night by merchants to protect valuables in their showrooms. A weak light in the room is necessary to detect moving shadow. Unlike light-dependent resistor-based (LDR) optical interrupt alarms, it does not require an aligned beam of light to illuminate the photodetector.

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 anywhere you need to monitor. Op-amp μA741 (IC1) is used as a voltage comparator. Its inversion inputs are polarized by the voltage obtained from the junction of the resistor 100k R1 and the collector of the phototransistor T1. The non-inverting input of IC1 obtains a controlled voltage from the potential divider R2 and VR1.

In the presence of ambient light, the phototransistor leads and the inverting input (pin 2) of IC1 obtains a lower voltage than its non-inverting input (pin 3). This causes the output of IC1 to be high, which is indicated by the brightness of LED1. When a shadow falls on the photosensor, the output of IC1 drops. This low pulse activates the monostable (IC2) designed for a 51 second delay using R6 and C3. The IC2 output is used to turn on LED2 and activate the alarm.

The slider switch S2 is used to select the buzzer or siren. When it is to the left, the buzzer beeps and when it is to the right IC UM3561 (IC3) is activated to give a loud alarm by simulating a police siren. The resistor R8 and zener diode ZD1 provide a DC of 3.1 V to the IC UM3561. The circuit is easy to assemble as it requires only a few inexpensive components. Lock in a cabinet with the photo sensor inside. Drill a 5 mm hole in the front panel of the cabinet to let the ambient light fall on the photo sensor. Set the VR1 potentiometer (47k) until LED2 stops flashing and the buzzer stops beeping while LED1 is lit. This is the position of VR1 that is maintained for that particular light intensity. LED1 will continue to glow even when a shadow is detected.

The circuit is ready to use. To test it, move a paper in front of the unit. If the LED2 lights up together with the buzzer's beep, it means that the photodetector has detected a shadow.

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