Application and implementation of the NE555 timer IC in the astable mode.
Principle involving the use and function of LDRs (Light Dependent Resistors) and their application.
Magic Eye
Price:(INR) -
100
Product Description
The Magic Eye circuit employs a simple mechanism to sound an alarm when a shadow falls on the LDR. This shadow could be that of a guest, intruder/burglar or cloud of smoke, depending upon the application.
Working:
In the circuit, the Light Dependent Resistor (LDR) varies its resistance corresponding to a variation in the intensity of light falling on it. Typically, when the light intensity is high they offer a high resistance. However, when a shadow falls on the LDR (i.e. the amount of incident light decreases), the resistance of the LDR rapidly falls.
Consider two cases:
1. In the absence of a shadow, light is directly incident on the LDR and its resistance is high. Since the NE555 timer IC is connected to operate in the astable mode of operation, this high resistance offered by the LDR generates an output signal at pin3, but not in the inaudible frequency range.
2. Conversely, when the shadow of a guest or an intruder is cast upon the LDR its resistance decreases. This change in the resistance of the LDR correspondingly alters the duty cycle of the oscillations generated at the output pin (pin3) of the NE555. The frequency of oscillations generated is now in the audible range and this is fed to the loudspeaker through the capacitor C1. The loudspeaker is basically a transducer that converts this oscillating electrical signal into sound vibrations. Hence, an alarm sound is generated by the loudspeaker to alert about the guest or intruder at the door.
Summary
The Magic Eye is a versatile electronic eye that can be used for a variety of applications like a burglar alarm, smoke detector or an automatic guest indicator. All these applications make use of the Light Dependent Resistor (LDR) which is installed and implemented differently in each case. Number of ICs used: 1.
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