![]() Here, the resistor used at each comparator is the 1k resistor. So the designing of this can be done by using resistors and a pot. In this meter, the adjustment of the reference voltage at the non-inverting terminal of the op-amp can be done using a voltage divider circuit. The main function of this comparator is to compare the voltage signal of audio through a reference voltage. This circuit can be designed with a number of dual op-amps like the LM358 IC, where each IC includes two comparators within it. This circuit operates with 9v to 12v DC however this IC also works with the voltages which range from 3v to 25v DC. According to the DC voltage, the LEDs will be turned ON and OFF at pin5 of the IC. The IC used in the circuit is a voltage level sensor that plays an essential role to drive all the LEDs at the output. In Dot mode, a single LED can be moved from top to bottom whereas, in BAR mode, all the LEDs will be turned ON serially. The selection of these modes can be done by using a switch S1. This circuit can be built with two modes of displays like DOT & BAR. This circuit uses an audio amplifier to generate an analog signal to drive 10 LEDs depending on the audio signals. By using this circuit, the level of the signal in the audio device can be displayed like a stereo system, the audio level of CD, etc. The circuit diagram of the VU meter using LM3914 IC is shown below. This circuit can be designed by using two op-amps like LM3914IC and LM358IC. The LED VU Meter using LM3914 and LM358 are discussed below. Once a waveform of speech is applied to this meter, then the movement will specify peaks & valleys within the signal. VU meters have a dynamic characteristic that estimates the human ear response. For complex waveforms like speech, these meters read among the values of average & peak of a complex wave. So these meters measure power levels in audio frequency signals by using special ballistics. To determine the signal level for avoiding overloading, distortion, and noise are used. These meters are used for operating systems like reproduction and sound recording.
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