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Zero-crossing
detector |
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Transistor: general purpose
pnp
This circuit gives out a short pulse each time the 220v
supply passes through zero. |
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N.B.
There is only one cut on the copper side of this
board; you should be able to see where it must be! |
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Modulator |
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The pulses are used to
set (start) a monostable (made using a CMOS 555 timer).
When the timed period is finished, the monostable resets
and gives a pulse which causes the triac to start
conducting. The time period of the monostable is varied
using a rectified and smoothed voltage taken from the
music source. Opto-isolator: MOC3020 or similar. Op-amp:
081. |
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The capacitor C determines the speed of
response of the system; try about 1µF.
If a low pass filter is connected to the input, the
light will be modulated by the bass notes in the music.
With a high pass filter, the light will respond the treble
notes. |
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