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Overview The circuit was designed to create a volume unit meter that would be used to measure the intensity of audio or sound level. Terminology - Volume Unit (VU) – an entity equal to a decibel for expressing the magnitude of a complex audio; it states the level of complex, nonrecurring, and non-periodic signals such as music and speech
- TL071 – a low noise JFET input operational amplifier with features such as common-mode input voltage range, high slew rate, operation without latch up, compensated internal frequency, high input impedance at the JFET input stage, low noise, low total harmonic distortion, protected from output short circuit, low input bias and offset currents, wide common-mode and differential voltage ranges, and low power consumption
- 7812 – 3-terminal 1A positive voltage regulator with short circuit protection, thermal overload protection, output transistor safe operating area protection, output current up to 1A, and output voltages from 5V to 24V
- BC550 – an NPN general purpose transistor with low current and low voltage used for low noise stages in audio frequency equipment
Circuit Explanation The circuit was constructed in a simple manner where the levels of audio signals are shown using the LED as optical or visual indicators of the level, which may be used for various applications. It can also be used with various levels of input signals which will be regulated by the presence of 100K Ohms trimmer TR1 while the gain is adjusted using the 4.7K Ohms trimmer TR2. The audio signal is being rectified by the diodes D1 & D2 where the negative periods of the signal are being cut off during the rectification process. This will in turn drive the main circuit of index that is made up of LEDs D3 to D13. Also attached to these LEDs are transistors Q2 to Q13 and other additional components around them. The visual indicators are made up of LEDs LD1 to LD13 which takes the signal from the optical index. They are distinguished from their colors red, yellow, and green. Every alteration on the audio signal level will cause each LED to turn ON as the voltage reaches approximately 0.65 V. With the use of complete index, the current requirement would be at 100 mA. The current might increase when more LEDs are added to the circuit. Just make sure that the current is enough to handle additional components. Application The use of VU meters may be found in broadcast studios as well as in recording studios where they are utilized to monitor the power levels of the sound. Because of this monitoring tool, the staffs and crews can decide whether to amplify or weaken the signal so that that it can be brought to optimal range. Typically, the VU meter is connected across the input of the amplifier or receiver. They are also an essential factor in the design of audio systems to provide proper audio adjustments. Source:users.otenet.gr/~athsam/vu_meter_1.htm
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