The circuit was designed based on the operation of Siemens UAA180 as it functions as a LED driver for light band displays for measuring the level of audio signals.
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 speechUAA180 – a bipolar integrated circuit used for driving 12 light emitting diodes where they form a light band that corresponds to the input voltage and are controlled similar to a thermometer scaleTL072 – 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 Circuit Explanation
The measurement of audio levels is showed with a scale where it is displayed by the use of a growing light band which is suitable for measuring approximate values. The passage of light between the two adjacent LEDs can be set between smooth and abrupt state while the brightness of the LEDs can be varied. These can be achieved by using an appropriate circuitry.
Within the region of IC2B is a circuit that provides precise rectification of the audio input signal. The calibration of the circuit is done with an interval or steps of 3 dB between one LED to another. This will make sure a very good rate of precision while measuring the entry of acoustic signals. The type of LEDs used can be of square shape and when they are arranged side by side with each other, it will look like a bar graph without spacing. The color of the LEDs consists of green, yellow, and red, which represents the level of the audio signals.
C1= 47uF 25V
|D1….8= LED GREEN
D9-10= LED YELLOW
D11-12= LED RED
The theory behind the design of this circuit does not only apply to VU meters, but also with field strength indicators, tachometers, level sensors, and other related instrument and equipments. When using for VU meter applications, the audio power levels in broadcast studios and recording are measured to determine the right amount of attenuation or amplification of signals for optimal outcome.