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Audio
light modulations add to the enjoyment of music during functions
organised at home or outdoors. Presented here is one such simple
circuit in which light is modulated using a small fraction of the
audio output from the speaker terminals of the audio amplifier.
The output from the speaker terminals of audio amplifier is
connected to a transformer (output transformer used in transistor
radios) through a non-polarised capacitor. The use of transformer
is essential for isolating the audio source from the circuit in
The sensitivity control potentiometer VR1 provided in the input to
transistor T1 may be adjusted to ensure that conduction takes
place only after the AF exceeds certain amplitude. This control
has to be adjusted as per audio source level. The audio signal
Proper earthing of the circuit is quite essential. The diode
bridge provides pulsating DC output and acts as a guard circuit
between the mains input and pulsating DC output. Extreme care is
necessary to avoid any electric shock
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