Sound Level Meter

Description

This is a one chip sound level meter that can be use for displaying 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.

Tips

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 bar graph display,Pin 9 can be should be disconnected from +V.

Parts List.
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

Audio Level Indicator

It is interesting to listen to your favorite music on a stereo system. It may be probably more interesting if you can watch the dancing lights along with the music. An effort has been made to try this idea with the help of a small circuit. The circuit is working satisfactorily for the last few months.

The circuit is described for one channel of the stereo amplifier. The other channel will of course be identical to it. A parallel point from loudspeaker of one channel is con­nected to the input of the three transistors! Fig. I). With 4.7k preset, the bias of T1, T2 and T3 is adjusted such that: (a) at low level of music only Tl conducts, (b) at medium level of music Tl and T2 conduct, Cc) at high level of music Tl, T2 and T3 conduct.

As Tl, T2 or T3 conducts, it extends a ground potential to its respective LED through a buffer amplifier. Now it is obvious that at low volume only LED1 will light, at medium volume LED 1 and LED2 both will light, and at high volume all the three LEDs will light. LEDO (green) will be lit per­manently to show that the channel is 'on'. Depending upon the liking, different colour LEDs can be used. 1C 7407 contains hex buffer amplifiers and hence one 1C is sufficient to accommodate both the channels.

Sound Level Meter

Sound Level Meter

This nifty sound level meter is a perfect one chip replacement for the standard analog meters. It is completely solid state and will never wear out. The whole circuit is based on the LM3915 audio level IC and uses only a few external components.

Schematic

Parts

Part Total Qty. Description

C1 1 2.2uF 25V Electrolytic Capacitor
R1 1 1K 1/4W Resistor
D1 1 1N4002 Silicon Diode
LED1-LED10 10 Standard LED or LED Array
U1 1 LM3915 Audio Level IC
MISC 1 Board, Wire, Socket For U1

Notes
1. V+ can be anywhere from 3V to 20V.

2. The input is designed for standard audio line voltage (1V P-P) and has a maximum input voltage of 1.3V.

3. Pin 9 can be disconnected from ground to make the circuit use a moving dot display instead of a bar graph display.