The Automatic Porch Light with Melody...
S&T - Light 002
The Automatic Porch Light with Melody automatically switches ON the porch light for a specific time duration to allow a person to park their vehicle in the garage . The circuit also generates a melodious sound for the time duration when the vehicle is being parked. No. of ICs used: 2
The heart of the Automatic Porch Light with Melody circuit is the NE555 timer IC which is triggered by the sound signals converted into electrical signals. Normally, trigger pin (Pin2) of the NE555 remains high. However, when this pin goes low, the NE555 get triggered to run as a monostable. This causes the output pin (Pin3) to go high for a specific time duration. This time period can be controlled by rotating the potentiometer VR1 (which forms a part of the timing circuit) to get different resistance values.
The condenser microphone picks up the sound signals from the horn of the vehicle and converts these to electrical signals, these are then amplified by the NPN transistor BC549 (T1). During the negative transition of the signal at the collector of transistor T1, the NE555 is triggered as a monostable and its output goes high to activate the melody generator IC UM66. The electrical signals generated by UM66 at its output pin (Pin1) is amplified by two NPN transistors BC547 (denoted as T2 and T3). These amplified signals are then fed to the loudspeaker which generates a musical tune for the set time duration.
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