A Volume Unit (VU) meter is a standard device that represents the signal level in audio equipment. This project; “VU Meter Circuit using ATmega32” makes the representation process much easier since it avoids the use of any physical medium to establish the connection in between the audio equipment or audio source and the circuit of the project. This way we can eliminate trouble of using more components. It uses a bargraph LED for visual representation of the audio.
Circuit and Working of VU Meter using ATmega32
The overall diagram of the complete project is illustrated in figure 1, where figure 2 illustrate power supply arrangement. As shown in the circuit diagram, we can clearly see that the heart of the project is IC1 which is a ATmega32A microcontroller. IC1 is surrounded by few other components like a bargraph LED (BAR1), a 1N4148 diode (D1), two transistors; BC547 (T1) and BD139 (T2), etc.
A linear voltage regulator circuit is made up of transistor T2, two diodes; diode D1 and zener diode ZD1 along with few other passive components. The power supply of 7-12V, 200 mA sources required for the device to operate is fed through the connector CON1. Combination of a diode D1 and capacitor C3 protects the circuit in reverse voltage connection and reduce the noise effects in the power supply, respectively. The zener diode (ZD1) current is fixed by the resistor R5. The voltage at the end of the emitter terminal of transistor T2 is found to be 4.9V.
Another transistor T1 is employed to construct a preamplifier circuit. Two resistors; R1 and R2 are used to adjust the gain as feedback resistor and set the collector current, respectively. Two coupling capacitors C1 and C2 are also used in the circuit.
This circuit captures the magnetic fields produced by the audio equipment when playing any music. Inductor L1(10µH) detects the magnetic field from the speaker and then passes to the preamplifier circuit for amplification. After that, the amplified output is transferred to the IC1 through analogue-to-digital converter (ADC) pin 40. The reference voltage of the ADC is fixed at 2.5V and the pre-amplified output voltage is always less than 2Vpp.
Finally, the output from the microcontroller (IC1) drives the bargraph LED (BAR1) which is linked with IC1 through Port C. The intensity of music can be determined from the number of LEDs glowing in the bargraph. Louder the music, greater is the number of glowing LEDs.
The project implements a simple program as C language to develop the source code, it is compiled using Atmel Studio 6.2. A program burner STK500 does the work of loading the source code of the program into the microcontroller using a hex code.
PARTS LIST OF VU METER CIRCUIT WITHOUT USING MICROPHONE
|Resistors (all ¼-watt, ± 5% Carbon)|
|R1 = 100 KΩ
R2 = 22 KΩ
R3, R4, R7 = 10 KΩ
R5 = 1.5 KΩ
R6 = 2.2 KΩ
R8 – R17 = 330 Ω
|C1, C2, C4 – C6, C9 = 100nF (Ceramic Disc)
C3 = 100 µF, 25V (Electrolytic Capacitor)
C7, C8 = 22pF (Ceramic Disc)
C10 = 100 µF, 16V (Electrolytic Capacitor)
|IC1 = ATmega32A (Microcontroller)
BAR1 =- 20-pin bargraph LED
T1 = BC547 (general Purpose NPN Transistor)
T2 = BD139 (NPN bi-polar Power Transistor)
D1 = 1N4148 (Switching Signal Diode)
ZD1 = 5.6V (Zener Diode)
|CON1 = 2-pin terminal connector
X1 = 8MHz Crystal Oscillator
SW1 = Push-to-on Switch
L1 = 10 µH ferrite-core inductor