A music-to-light modulator is a circuit which controls the
intensity of one or more lights in response to an audio
input. The problem in older circuits is that there was a
direct electrical connection between the lights using mains
voltages (110 to 250V AC) and the amplifier circuit low 9
to 12 voltage levels. Any fault in the high voltage circuit
could completely destroy the low voltage section (and
give a nasty shock to anyone holding it.)
This potential problem has been overcome using the
optocoupler. There is no electrical link between the two
parts of the circuit. This kit introduces the opto-triac
(3021) which is a further development of the optocoupler.
An audio input controls a LED.
Click here to download the full size of the above Circuit.
The diagram shows how simple the circuit is. The audio
signal is applied across the LED of the opto-triac. The
potentiometer adjusts the input sensitivity while the
resistor is used as protection from high signal peaks. The
LED emits infra-red light in response to the input signal.
The triac driver inside the 3021 package is sensitive to
this IR light which activates a slave triac and load.
Input trigger voltage ............................2.3 - 2.5V (min)
AC input voltage..................................110V - 250V AC
Load (max) ..........................................500W @ 250V
220W @ 110V
WHAT TO DO IF IT DOES NOT WORK
First disconnect the board from the mains supply.
Unplug it completely.
Poor soldering is the most likely reason for the problem.
Check all solder joints carefully under a good light. Next
check that all components are in their correct position on
the PCB. Is the optocoupler chip in the correct way? Is the
potentiometer wound around too far?
Reconnect the AC mains supply. Carefully use a
voltmeter, follow around the tracks to check the potential
differences at various parts of the circuit. Maybe the input
signal is not enough to drive the optocoupler. It needs
1.2V and a current of 5mA (approx). A small tape
recorder or radio will need an amplifier stage to amplify
the signal before supplying it to the audio input. The light from the LED
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