What is a sound level meter?

A sound level meter is handy equipment used to display sound levels. There are wide ranges of these devices; some show a digital numerical output of how many decibels of sound are created while some other shows a bar graph indicator (the decibel meter you see in mission impossible 1 movie). Here in this project, we are going to construct a sound level meter that displays a bar graph using 10 LEDs.


This is a one-chip sound level meter that can be used for displaying the sound level of an amplifier or simply the sound level from a microphone. The heart of the circuit is  IC LM 3915 Audio level IC. Even though it is a stand-alone IC, a peak detector based on Transistor BC 558  and diode 1N4001  is also included for better performance.


The supply voltage can be from 3V to 20V. The input is set for audio line voltage (1V peak to peak) and has a max input voltage of 1.3V.   To make the circuit use a moving dot display instead of the bar graph display, Pin 9 can be should be disconnected from +V.

If you are interested in building more audio circuits, try your hand in our USB sound card circuit application. You can also try our low-cost mike mixer and the baxendall tone control circuit.

Parts List – Sound Level Meter Circuit

C1                            2.2uF 25V Electrolytic Capacitor
C2, C3                    0.1uF Ceramic Disc Capacitor
R1, R3                    1K 1/4W Resistor
R2                          10K 1/4W Resistor
R4                          100K 1/4W Resistor
R5                          1M 1/4W Resistor
D1                          1N4001 Silicon Diode
Q1                         BC 558 PNP Transistor
LED1-LED10       Standard LED or LED Array
U1                         LM3915 Audio Level IC
MISC                    Board, Wire, Socket For U1

Sound Level Meter Circuit Diagram.

Sound Level Meter Circuit/Acoustic Level Meter

If you are learning to be a communication engineer, playing with audio circuits is very important. This sound level meter is a simple hobby circuit to start with. You should build amplifier circuits and filter circuits to get a good grip on the subject.



  1. Carlos Senna

    I need to build a current level indicator with colors leds showing the current level. Seeing your circuit above I guess that maybe it could be adapted to my needs. So I ask you if you have a specific circuit to meet my needs or if you can give me directions to change this one to my needs.
    Thnks a lot

  2. Does it work with a PC. And if not, how sould I change it?

  3. Hi Howre
    Try to connect 2 9v bateries in series. This IC needs more power to work fine.
    This circuit will work just for one channel. Chose left or right and connect it at the “input”. The ground must be connected to the ground of the circuit.
    Hope it is clear.

  4. hey there, ive tried your way, but i have a huge problem!!! as i connect the “project” to 9v, only 7 of my leds work(which is stupid cause they are working great!) other thing is it does not react to sound!!! what could be the problem?
    and in this circuit, input ? what does it mean? cause in the input there is 3 ,ground left and right… what is the right way to connect them?