Light Chaser Circuit

This light chaser circuit (music-operated lighting effect generator) comprises five sets of 60W bulbs that are arranged in zig-zag fashion. The bulb sets glow one after another depending on the intensity of the audio signal. No electrical connection is to be made between the music system and the lighting effect generator circuit. You just need to place the gadget near the speakers of the music system.

The circuit is powered by regulated 9V DC. The AC mains is stepped down by transformer X1 to deliver a secondary output of 12V AC at 250 mA.

Light chaser circuit diagram

Light chaser

When you put your music system in front of the condenser microphone of the light chaser, the sound pressure variation is converted into electrical signals by the condenser microphone. The amplified output is fed to IC LB1403 (IC3) at its input pin 8. IC3 is a five-dot LED level meter commonly used in stereo systems for LED bargraph displays. It has a built-in amplifier, comparators and constant current source at its output pins.

Pin config

Depending on the intensity of the input audio signals, all or some outputs of IC3 go low to drive transistors T1 through T5, which, in turn, fire the corresponding triacs TR1 through TR5 via their gates and multicoloured zigzag bulb sets comprising ZL1 through ZL5 glow.
When the audio level is low, only triac T1 is fired and the zig-zag bulb set ZL1 turns on and off sequentially. When the audio level is high, triacs TR1 through TR5 get fired and all the bulb sets (ZL1 through ZL5) turn on and off sequentially.

Pin 7 of IC3 is used for selecting the response speed of the lighting. The larger the time constant, the slower the response, and vice versa. The time constant can be changed by changing the values of resistor R6, variable resistor VR2 and capacitor C7. Here, variable resistor VR2 is used for varying the response speed of the chaser light as desired. When VR2 is set in the minimum resistance position, the response is very fast, and when it is set at the maximum resistance, the response is slow.

The complete light chaser circuit including the power supply can be constructed on any general-purpose printed circuit board or a small Veroboard. Triacs TR1 through TR5 should be kept away from the op-amp and its related components. The metallic parts of the triacs should not touch each other and the other parts of the circuit. After assembling the circuit, house it in a suitable shockproof plastic cabinet. Make some holes in the cabinet for heat dissipation.

Never touch any naked part of the circuit when it is connected to the mains.

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