This is a type of meter to display the level of an input audio signal. It makes use of the National Semiconductor LM3916 bar graph/LED driver chip. This chip is a complete LED VU meter driver chip. This circuit uses just one IC and a very few number of external components. It displays audio level in terms of 10 LEDs.

An audio signal is a representation of sound waves in a different form. Typically this is an electrical voltage, but these signals can be expressed through alternative mediums such as magnetic particles, when recorded onto analogue tape; or as RF waves, when broadcast through radio.

We are exposed to sound throughout each moment of every day regardless of whether we pay attention to it or not. The sounds we hear give insight into not only their sources but also the nature of our physical environment—surrounding objects, walls, and structures. Sound travels through the air as longitudinal waves. Molecules of air vibrate, changing their distances between each other. When they come closer, they are known as compressions. When they move further, they are known as rarefactions.

Most humans have two ears, duh. If sound was recorded with two separate microphones and played back with two separate speakers, you could possibly reproduce the same illusion of left-to-right direction for sound reproduction. This is why stereo was created: the common implementation of sounds recorded with two channels: left and right.

These audio level meter programs allow the optimum setting of input levels for various sound recording functions, particularly for video editing on computer system. When capturing video and sound from different sources accurate level setting helps maintain a consistency of volume across various clips, and therefore eases the sound mixing.

The circuit is quite simple; it is more or less the same as that given in the datasheets of the chip. The LM3916 is fully configurable through the use of external components.

The LM3916 VU-meter chip can drive the LEDs in either dot mode or bar mode, which is selected by connecting pin 9 to Vcc (Bar mode) or leaving it open (Dot mode). But we use the LB1403N IC, which can derive 5 LEDs just in bar mode.

This IC is capable of use as: AC level meters such as Volume Unit meters. DC level meters such as signal meters.

Type No. Lightning sensitivity Comparator level Constant LED current LB1403 N 85 nVrms Type +6Db, +3dB, 0dB, -5dB, - 10dB 15 mA Type LB1413 N 105 nVrms Type 1.67Vc3, 1.33Vc3, Vc3, 0.67Vc3, 0.33Vc3 15 mA Type LB1423 N 85 nVrms Type +6Db, +3dB, 0dB, -5dB, - 10dB 7 mA Type LB1433 N 105 nVrms Type 1.67Vc3, 1.33Vc3, Vc3, 0.67Vc3, 0.33Vc3 7 mA Type LB1443 N 85 nVrms Type+6Db, +3dB, 0dB, -6dB, - 12dB 15 mA Type

Internal structure of IC LB1403N is shown in the following diagram:

Capable of generating a bar-display for input voltage with 5 LEDs. Operates from either AC or DC input voltage because of on-chip rectifier amplifier. Lightening level remains stable to line regulation because of on-chip voltage reference. LEDs are driven by a constant current; stable to line regulation.

Power supply range is wide (3.5 to 16v) for a wide range of applications. Five types of ICs constitute the series with various lightning levels of the LEDs and driving currents. SEP-9 pin package and fewer externally connected components results in smaller space requirements on the circuit board. Low noise at LED lighted mode.