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 for sound level meter


Total Qty.
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


  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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Sound Level Meter
Sunday, October 12, 2014 4:58:58 AM
I want to make a sound level circuit for detecting noise source under a car bonnet (or wherever it might be). Can I use electret microphones with a switched input from mic to mic and thus see which is nearest the noise source?
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.
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.
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??
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.)

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")
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?
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.
Sound Level Meter
Wednesday, January 27, 2010 12:16:39 PM
Just received some RGB LED's from someone made by this company: 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 :-)
Sound Level Meter
Sunday, August 23, 2009 4:02:39 AM
Yet another circuit on this site which doesn't work. Nice one..

(Editor's notes: Works fine. See multiple posts in the forum. )

Sound Level Meter
Thursday, July 23, 2009 7:10:17 AM
can i connect it to a mike to check the audio level of a person singing into it(mike)?
Bradley Glen
Sound Level Meter
Saturday, July 04, 2009 11:49:05 AM
I tried this and the problem is that the diode is forward biased through the Diode from the supply . If any DC leaks onto pin 5 of the IC then you are not going to get the proper reading .
Sound Level Meter
Friday, June 19, 2009 9:28:18 AM
The Q1's bias will not work if the Vin is less than about 0,6V... try an auto bias circuit using the V+ insead of Vin... Then remember that the D1 introduce a voltage drop of about 0.7 V
Sound Level Meter
Saturday, March 21, 2009 5:00:25 PM
Putting an audio signal in makes no difference. Also when I connect the power all LEDs turn bright on too how can I fix this? Any help would be appriciated,
Sound Level Meter
Sunday, December 28, 2008 10:28:02 AM
Hi, i'm new in this kind of things, but have always loved electronics, actually thats what im going to study when i graduate, but i have two questions, all of those triangles pointing down are ground conections, right? And the second is what kind of input can i use and how do i connect it? Can i use a normal rca jack microphone, an electret microphone or what?
Sound Level Meter
Tuesday, December 09, 2008 5:09:45 PM
Built several of these, Works great. Thanks!
Sound Level Meter
Thursday, October 09, 2008 12:03:06 PM
1N491 diode is not available here. can you give me another as a substitute because the circuit doesn't work. i just used 4148 diode. is it ok? pls response.. tnx!
Sound Level Meter
Tuesday, August 26, 2008 8:23:39 PM
I have just built this project and i can't seem to get it to work. The problem is there are some many errors I could make here. I have a feeling it is either the PnP transistor, or the Silicon Diode. If u can help me out, plus email me.
Sound Level Meter
Saturday, August 02, 2008 11:06:29 AM
looks nice but when i turn the power on all LEDs glow bright too, anyone knows how to fix it? thanks
Sound Level Meter
Tuesday, June 03, 2008 11:33:30 AM
Thanks for the circuit works well
Sound Level Meter
Friday, May 23, 2008 1:36:23 AM
It works. Used 100k pot for R4.
Sound Level Meter
Tuesday, May 20, 2008 9:11:28 AM
Thanks for the site, though im having a few problems with this circuit. I have tried making a stripboard of it and now just tried a PCB. WIth each, all of the LEDs light brightly when the voltage is supplied. Putting an audio signal in makes no difference. Any help would be appriciated, cheers.
Sound Level Meter
Friday, March 21, 2008 1:19:03 PM
The circuit will work with any little PNP transistor. The old version of the project doesn't work.
Sound Level Meter
Sunday, January 13, 2008 3:26:11 PM
i'm finding it difficult to get the transistor so pls send me the circiut diagram of the older version
Sound Level Meter
Tuesday, November 13, 2007 4:28:57 AM
PLEASE help me to get dB METER for 0 - 150 dB, Thanks.
Sound Level Meter
Wednesday, October 24, 2007 8:35:49 AM
I have not built circuit but for those who say it doesn't work may need some audio signal info. Pro-Audio vs Consumer Product Audio line levels are different. Consumer product line standard outputs is -10dBv = .316 Vrms = 0.9 Vp-p. ProAudio line outputs is 1.78dBv = 1.23Vrms = 3.47 Vp-p. So this circuit is more appropriate for cheap consumer products to monitor RCA outputs. You should consult your equipment for actual output levels. e.g. Tape monitor output on my stereo is .150 Vrms and VCR output is 1.0 Vp-p and my mixer line outputs is 1.55 Vp-p when controls are at 70%. Looking at the circuit I would think the right diode would be important. Don't regular silicon diodes drop .7v when forward biased.
anonydr mahamad zayedmous
Sound Level Meter
Saturday, October 13, 2007 11:00:20 PM
dear sirs i would like to know how to measure soud level meters frpm dental turbine? thanks urs dr mahamad
Sound Level Meter
Sunday, September 30, 2007 5:44:48 PM
give correct circuit and stop deceivine us the doesn't work
Sound Level Meter
Saturday, September 22, 2007 2:02:23 AM
is the diagarm works?somebody said its not.! can pls do me a schematic diagram like that(sound level meter) that can use as switch of an airCondition unit depending on the noise of a room...
Sound Level Meter
Wednesday, September 05, 2007 1:34:44 PM
nonsense circuit
Sound Level Meter
Sunday, August 12, 2007 8:13:27 AM
it does not work
Sound Level Meter
Friday, July 27, 2007 8:45:58 AM
is the sound level meter's readings/findings displayed?
Sound Level Meter
Tuesday, July 24, 2007 9:58:11 PM
i would like to build an SPL meter that has an output in terms of decibel readings. Say if the noise reading reached 80dB a voice alarm will be activated. how will im able to do this. can you send me a circuit diagram for that kind of design. thanks!!!
Sound Level Meter
Wednesday, July 11, 2007 7:57:26 AM
The sound lever was was quite good and it all worked out well with an amplifier of high wattage.I built the circuit and was nice.
Sound Level Meter
Monday, July 02, 2007 10:54:52 AM
I would like to make a "fun" circuit that would sound an alarm when the noise in a room gets to loud. How would you suggest I do this?
Yvon Chartrand
Sound Level Meter
Sunday, July 01, 2007 11:45:35 AM
I have built it and it does not work, probably because I try to monitor the line level of the amplifier, and maybe because the input impedance should be adjusted. I do not know how to correct the situation. Any one can help me?Thanks for reading. Yvon Chartrand
Sound Level Meter
Monday, June 25, 2007 3:50:37 AM
ok i think this is a nice circuit.. i make this as my project..
Sound Level Meter
Friday, June 15, 2007 8:14:37 AM
it doesn t work...contect me for very circuit
Ali - Bahrain
Sound Level Meter
Thursday, May 31, 2007 2:15:38 AM
The one thing I need to know is how to adjust this circuit to adabt with my sound source .. Because as you know, the audio which comes from 50W amplifier is too larger than 2W amplifier, so I think we need to a variable resistor to adjust the strength of income signal & then the IC is programed with correct sound level. This chip "LM3915" provides a logarithmic 3 dB/step analog display >> Anyway, I don't construct this circuit at the present; maybe I do it in the future.
Sound Level Meter
Sunday, May 20, 2007 9:15:10 AM
Could you give me more details of this circuit
Sound Level Meter
Thursday, May 17, 2007 12:50:18 AM
Sound Level Meter
Thursday, May 03, 2007 7:03:15 AM
Sir plz full description of sound level meter and operation of circuit
Sound Level Meter
Monday, April 30, 2007 2:53:21 PM
what could be wrong if all the leds are on? how does it soupuse to capture sound ? i think i need more information could you help me?
Sound Level Meter
Thursday, April 05, 2007 11:42:12 AM
if you are having trouble making this work, one problem may be your LED orientation. diodes work only when orientation is correct, the positive side (longer lead) should be on the rail side and not the IC side. LED orientation is denoted in the same way that normal diode orientation is noted. but people tend to ignore this notation for LEDs.
Sound Level Meter
Friday, March 30, 2007 7:27:25 AM
it works make sure you connections are proper and correct diode directions
Sound Level Meter
Friday, March 30, 2007 7:17:47 AM
VERY Good Great thing I did it for science fair project :)
Sound Level Meter
Saturday, March 24, 2007 4:30:17 PM
It Doesn't work !!
Sound Level Meter
Thursday, March 22, 2007 6:18:42 PM
Doesn't Work!!!!
b.jagadeesh kumar
Sound Level Meter
Saturday, March 03, 2007 5:55:26 AM
very good 9885740831
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