Music to light modulator circuit

Posted on Jun 15, 2012

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.

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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. SPECIFICATIONS 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 drives a...

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