Sound Level Meter


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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. This circuit can also be integrated into audio amp projects.

Schematic

Schematic for sound level meter

Parts

Part
Total Qty.
Description
Substitutions
C112.2uF 25V Electrolytic Capacitor
C2, C310.1uF Ceramic Disc Capacitor
R1, R321K 1/4W Resistor
R2110K 1/4W Resistor
R41100K 1/4W Resistor
R511M 1/4W Resistor
D111N914 Silicon Diode
Q112N3906 PNP Transistor
LED1-LED1010Standard LED or LED Array
U11LM3915 Audio Level IC
MISC1Board, 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 +V to make the circuit use a moving dot display instead of a bar graph display.
  4. Thanks to help from the forum, this circuit has been improved from the original version to include a peak detector for a more stable and viewable output. This page has been updated with the new circuit.

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Comments

Add A Comment

anonymous
Sound Level Meter
Sunday, February 24, 2013 3:33:30 PM
I am having the problem "of about 0.6V to pin 5". Regarding "The solution is quite simple though.", please share. I am using a microphone into an LM386. Without the Peak Detector it works as expected. If at all possible I would like to stick the the LM386. The only purpose for my circuit is to make the bar graph respond when someone speaks into the mic. I am not using the sound in any way (not even playing it into a speaker). Thanks!
peter west
Sound Level Meter
Monday, July 09, 2012 3:30:55 AM
I agree that the peak circuit is shown in the data sheet. I also agree it does not work. There is a good reason why not - the Vbe for the transistor is about 680mv, while the voltage drop across the diode is only 120mv [because there isn't any current with no input] The resulting 500mv+ turns all the leds on, as a number of people has remarked. The solution is quite simple though.
anonymous
Sound Level Meter
Friday, July 06, 2012 3:20:18 PM
This circuit WILL NOT WORK for line level signals; there will be a constant voltage of about 0.6V to pin 5, which will keep the lowest LEDs on constantly. Don't bother building this - use an opamp detector instead.
Pio
Sound Level Meter
Tuesday, April 03, 2012 8:16:44 AM
could any1 help me make a sound level meter that goes up to eleven? 11 LEDs that is. can this b altered to do so? also is it possible to add a Pezio elctric microphone to this circuit diagram??
anonymous
Sound Level Meter
Thursday, December 01, 2011 2:46:05 PM
Does it matter if you use Carbon or Metal film resistors?

(Editor's notes: Nope.)

Dimitris
Sound Level Meter
Sunday, August 08, 2010 8:46:35 AM
I think that u connect 5 with 3. There is no connection between them. 9 is directly connected to 3. (" All LED switches on when power is connected")
anonymous
Sound Level Meter
Thursday, June 03, 2010 10:48:17 AM
Built this circuit but it does not work properly. All LED switches on when power is connected. Any workaround for this problem?
Eric
Sound Level Meter
Sunday, April 11, 2010 9:12:47 PM
I built this exact circuit using a 15V power supply and my LM3915 is overheating very badly. I am using a 1N4148 instead of the 1N914 but otherwise it is all the same. Does anyone have any ideas as to why this is happening? Also, before it gets too hot all the LEDs are lit when no audio signal is present. This would seem to indicate incorrect wiring but both I and another individual have checked it thoroughly. A photo of circuit with all wiring can be provided if needed.
jcs
Sound Level Meter
Wednesday, January 27, 2010 12:16:39 PM
Just received some RGB LED's from someone made by this company: http://www.lumiron.com/SPECTRO%20300RGB%20-%20T.html I would like to try to drive them with this Sound Level Meter circuit. The supply voltage for the LED's is 12 volts, so it should work fine. Any ideas or suggestions would be much appreciated. I figure 16.7 million colors is enough color to experiment with!!! LOL!!!
J & R
Sound Level Meter
Tuesday, November 17, 2009 8:41:26 PM
This circuit is basically the reference circuit and the reference peak detector from the LM3915 Datasheet. For those who claim it will not work, I was wondering, why then would the same circuit be contained in the LM3915 datasheet, from the manufacurer of the I.C.? The answer has to be that the circuit works. Actually, I've been building these for awhile (blame Mr.MIMs III) and they work fine. For the person who asked, the 1N4148 is a fine replacement for the 1N914 in this circuit (even the datasheet says so). Have a good day :-)
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