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.
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.
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.