CMYK
CIRCUIT
IDEAS
MUSICAL LIGHT CHASER S.C. DW
IVEDI
DEBARAJ KEOT ranged in zig-zag fashion. The bulb lighting effect generator circuit. You
sets glow one after another depending just need to place the gadget near the
T
his music-operated lighting ef- on the intensity of the audio signal. speakers of the music system.
fect generator comprises five No electrical connection is to be made Fig. 1 shows the complete circuit
sets of 60W bulbs that are ar- between the music system and the of the musical light chaser, while Fig.
Fig. 1: Circuit diagram of musical light chaser
82 • JANUARY 2005 • ELECTRONICS FOR YOU WWW.EFYMAG.COM
CMYK
CIRCUIT
IDEAS
2 shows pin configurations of 9V regu- The time constant can be changed by
lator 7809, triac BT136 and level meter changing the values of resistor R6,
IC LB1403. variable resistor VR2 and capacitor
The circuit is powered by regulated C7. Here, variable resistor VR2 is used
9V DC. The AC mains is stepped down for varying the response speed of the
by transformer X1 to deliver a second- chaser light as desired. When VR2 is
ary output of 12V AC at 250 mA. The set in the minimum resistance posi-
transformer output is rectified by a tion, the response is very fast, and
full-wave rectifier comprising diodes Fig. 2: Pin configuration when it is set at the maximum resis-
D1 and D2 and filtered by capacitors tance, the response is slow.
C1 and C2. Regulator IC 7809 (IC1) plifier, comparators and constant cur- The complete circuit including the
provides regulated 9V power supply rent source at its output pins. power supply can be constructed on
to the circuit. Closing switch S1 pro- Depending on the intensity of the any general-purpose PCB or
vides power to the circuit and LED1 input audio signals, all or some out- a small Vero board. Triacs TR1
glows to indicate that the circuit is puts of IC3 go low to drive transistors through TR5 should be kept away
ready to work. T1 through T5, which, in turn, fire the from the op-amp and its related com-
When you put your music system corresponding triacs TR1 through TR5 ponents. The metallic parts of the
in front of the condenser microphone via their gates and multicoloured zig- triacs should not touch each other and
of the light chaser, the sound pressure zag bulb sets comprising ZL1 through the other parts of the circuit. After
variation is converted into electrical ZL5 glow. assembling the circuit, house it in a
signals by the condenser microphone. When the audio level is low, only suitable shockproof plastic cabinet.
These weak electrical signals are am- triac T1 is fired and the zig-zag bulb Make some holes in the cabinet for
plified by op-amp µA741 (IC2), which set ZL1 turns on and off sequentially. heat dissipation.
is configured as an inverting ampli- When the audio level is high, triacs Note. 1. Some zig-zag lights have
fier. Using preset VR1 you can set the TR1 through TR5 get fired and all the a special bulb called ‘master bulb’ for
sensitivity of the circuit. bulb sets (ZL1 through ZL5) turn on automatic flickering. It should be
The amplified output is fed to IC and off sequentially. removed and replaced with a simple
LB1403 (IC3) at its input pin 8. IC3 is a Pin 7 of IC3 is used for selecting non-flickering colour bulb.
five-dot LED level meter commonly the response speed of the lighting. 2. Never touch any naked part of
used in stereo systems for LED The larger the time constant, the the circuit when it is connected to the
bargraph displays. It has a built-in am- slower the response, and vice versa. mains. z
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