ABSTRACT
Sound, physical phenomenon that stimulates the sense of hearing. In humans, hearing takes place whenever vibrations of frequencies between about 15 and 20,000 hertz reach the inner ear.., and the term sound is something restricted to such airborne vibrational waves.
The purpose of the project is to implement a level indicator of sound signals corresponding to the variation in intensity. When we keep the music system in front of the condenser microphone of the light chaser, the sound pressure variation is converted into electrical signals . These weak electrical signals are amplified. It is fed to a comparator IC. Depending on the intensity of the input audio signals, all or some outputs of IC go low and multi-coloured zigzag bulb sets.
INTRODUCTION
This music-operated lighting effect generator comprises ten 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 lighting effect generator circuit
When we keep the 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. These weak electrical signals are amplified by op-amp µA741, which is configured as an inverting amplifier. The amplified output is fed to IC LM3914 at its input pin 5. It is a ten-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.
Depending on the intensity of the input audio signals, all or some outputs of the IC go low to drive transistors T1 through T10, which, in turn, activate corresponding triacs TR1 through TR10 and multicoloured zigzag bulb sets comprising ZL1 through ZL10 glow.
The complete circuit including the power supply can be constructed on any general-purpose PCB or a small Vero board.
BLOCK DESCRIPTION
1. POWER SUPPLY
The power supply circuit consists of a step-down transformer, a full wave rectifier circuit, regulator IC, filter and a zener regulator.
Transformer
The input 230 V ac main is step down to 12v ac by a centre tapped step down transformer. It produces 12V, 250mA.
Rectifier Circuit
The output of the transformer is fed to the rectifier circuit. The full wave rectifier rectifies the sinusoidal input to DC output which contains ripples.
Filters
The ripples contained in the DC output of the rectifier are filtered using capacitors.
Regulator IC
The filtered output is given to the Pin No: 1 of the regulator IC. Here LM7812 is used. The regulated output is taken from Pin No:3. The regulated output is 12 V.
2.MICROPHONE
The microphone used is condenser type. It receives the sound signals and the pressure variations are converted into electrical signals.
3 . AMPLIFIER
The amplifier is realized using µA 741 IC. The opamp is used in the inverting mode. It amplifies the weak electrical signals which is fed to the input pin of the comparator IC.
4 Ten level Comparator
The amplified output is fed to the comparator IC. The IC LM3914 is used as the ten level comparator . It compares the input voltage with the reference voltage and the output pins go low in accordance with the intensity of the input signal.
5 Lamp Driver Circuit
The driver circuit consists of a set of PNP transistors, triacs etc.
The output of the comparator IC is active low. When any of the pin is at low state the corresponding transistor will be switched on.
This will fire the corresponding triacs via there gates and thus the lamps Z1 to Z10 glows according to the intensity of the sound signals.
CIRCUIT DIAGRAM
DESIGN
Transformer:-
A 230V 12-0-12 transformer with a secondary current of 500mA. Now randomly opt for E & I cores. The winding area A (product of length l and breadth of bobbin on which the winding is to be made) is the product of tongue width of the E section and stacking width.
A= Tongue width * Stacking width.
Efficiency of the transformer is 80-90%.
Primary input = Secondary VA/efficiency.
Cross sectional area of the core=√(P/B).
P= input power & B= flux density.
No: turns per volt=1/(4.44fBA), where
f=frequency, A=cross sectional area , B=flux density.
No: of primary turns=No: of turns per volt * V1.
No: of secondary turns = No: of turns per volt * V2.
For centre tapping = No: of secondary turns/2
As the thickness of the gauge increases the thickness will decrease and vice versa.
Operation of circuit
The musical light chaser circuit consists of a power supply circuit, a receiver, Microphone, an amplifier circuit, a comparator IC (LM3914) and the lamp driving circuit.
Power Supply Circuit
The power supply circuit consists of a step down transformer, a Full wave rectifier, a regulator IC LM7812 and a filter circuit.
The 230V ac mains voltage is stepped down by a 12-0- centre tapped step down transformer into 12V, 250mA ac voltage. The voltage obtained at the output of the transformer is the rms value. The output of the transformer is fed to the rectifier circuit. It consists of four diodes. The full wave rectifier rectifies the sinusoidal input to DC output which contains ripples. The ripples contained in the DC output of the rectifier are filtered using capacitors.
The filtered output of the full wave rectifier circuit is given to pin no 1 of the regulator IC LM 7812. The output of the regulator IC is taken from pin no 3 . This output is then filtered using a capacitor filter.
CONDENSER MICROPHONE
The microphone used is condenser type. It is used as a receiver. It receives the sound signals and the pressure variations are converted into electrical. A biasing circuit consisting of resistors is used to bias the microphone.
The output of the microphone is passed through a coupling capacitor to eliminate the DC components.
AMPLIFIER CIRCUIT
The amplifier circuit consists of an opamp, µA 741 IC. The opamp is used in the inverting mode. It is a linear IC. The output of coupling capacitor is given to the inverting terminal of the amplifier, it is the pin no 2. The pin no 3 is grounded. The weak electrical signals at the output of the microphone are amplified by the inverting amplifier which is fed to the input pin of the comparator IC.
TEN LEVEL COMPARATOR IC
The comparator IC used is LM3914. It consists of a built in amplifier, comparators and a constant current source at its output pins. It is a level meter which is commonly used in the stereo systems. In this circuit the comparator is used. The output of the inverting amplifier is given to the input pin no 5 of the comparator IC.
The reference input voltage to the comparator is given at the pin no 3 of LM3914. The maximum reference voltage is 3.3V. At the output of the power supply circuit a zener diode is connected in parallel to convert the 12Vdc to 3.3V .This voltage is used as supply voltage for the comparator IC.
The IC contains a set of ten comparators. The 3.3V voltage is divided among them. The IC can be operated in two modes i.e, bar graph mode or in dot mode. The mode can be selected through the pin no 9. When the pin is grounded the IC is operated in dot mode and bar graph mode when it is kept open.
The input voltage is compared with the voltage that is divided between the resistors. When the input voltage exceeds 1/10th of the reference voltage output of the first comparator go low. When the input voltage exceeds 2/10th , the output of the second comparator go low. Like wise when the input voltage equals the reference voltage all the output pins will be low. Here the bar graph mode is used.
Lamp Driver Circuit
The driver circuit consists of a set of PNP transistors, triacs resistors etc.
The output of the comparator IC is active low. When any of the pin is at low state the corresponding transistor will be switched on.
This will fire the corresponding triacs via there gates and thus the lamps Z1 to Z10 glows according to the intensity of the sound signals.
CONCLUSION
The musical light chaser is used in decoration purposes of parties etc. It can also be used in rooms to indicate the level of noise. Generally inside libraries, hospitals, classrooms etc:- where high noise is not preferable.