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Electronics Project help - LED VU Meter

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Electrophile07

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Hey guys, I need to build an LED VU Meter for my electronics project which I have to submit by the coming week. I searched quite a lot on instructables and on youtube to see how it is and all, but frankly I'm spoilt for choice. I found this one linked below which I liked and I have all the components ready with me to build it, but earlier in the day today I realised that it was a Sound Level Meter ( I donno the difference). http://www.aaroncake.net/circuits/vumeter.asp
I want to make one which can react to the beats of music ( you know what I mean :p )
Well I wanted to know whether the one given on the aaroncake website will work in such a way or not.....I have been an electronics student for 2 years but have not got exposure to these type of projects...

I also want to know how I am supposed to apply an audio input to the circuit....it says input but how do I apply it? Also I will be testing the circuit given on the aaroncake website tomorrow so I was thinking of using the signal generator present in my lab as an audio input but then again I dont know what frequencys to apply......
Can anyone please help me sort out these issues? Any help would be greatly appreciated!!

PS - these 2 links also show a similar Vu meter posted by Audioguru on other threads, are they of any use to me?
http://www.electro-tech-online.com/attachments/vu-meter-with-gain-png.32468/
http://www.electro-tech-online.com/attachments/vu-meter-png.32467/
Thanks!
 

audioguru

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The input transistor on the Aaron Cake's circuit does not work properly unless the signal level is very high but the LM3915 is not set up for such a high input level.
The input opamp on the "VU Meter With Gain has gain that is too high for most uses.
The "VU Meter" is Aaron Cake's circuit again.

You need a VU meter circuit with an input volume control. Then you can feed it signals from a CD or MP3 player or turned down you can feed it from the speaker wires of a stereo.

I have a VU meter with a microphone. It also has an automatic level circuit that boosts its range. It is this one:
 

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Electrophile07

New Member
Thanks for the help, Audioguru.....but that is one hell of a complicated looking circuit to me.....is there anything simpler that I can try? I forgot to mention, but along with making the project, I must also be able to explain the use of each and every component in case they ask it in the vivas....so I was looking for something which was similar to the one posted by AaronCake (not very complicated)...
Any help with that?
 

audioguru

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Most Helpful Member
Here is a very simple VU meter. The datasheet for the LM3915 explains what the parts are for but ask here if you need an answer.
 

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Electrophile07

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Yeah I think I'll try that out and get back to these forums in some while.....in the meantime, how do I apply the audio input as I asked before?? Suppose I want to connect my phone/mp3 player then how do I physically connect it to the input?
 

audioguru

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Your phone has a jack for headphones so buy a cable that fits the jack and connect its wires to the input of the VU meter.
Your MP3 player has an output jack so buy a cable that fits the jack and connect its wires to the input of the VU meter.
The jack and cable is stereo (two channels) but the VU meter is mono (one channel) so mix the two stereo channels together with two series 10k resistors to make mono.
 

Electrophile07

New Member
Could you please show a diagram as to how you are supposed to 'mix' the two stereo channels together with 10k resistors to make mono??
All I know is that my phone has the 3.5mm jack from which I can obtain 2 wires (by using some old earphones and cutting them) so how do I do the mixing bit?

Lastly, I found another Vu meter on youtube which seems quite good too....
Here are the schematics taken from the same video......here again my problem is the audio input part, the rest of it I have understood quite well.
Thanks for all the support uptill now, you have been really kind Sir...
Schematic - VR1 is a 10k pot
 

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audioguru

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You talked about and showed videos of the VU meter LEDs responding only to THE BEAT and not to the music. Then the circuit is fed from a sub-woofer amplifier or it has a very good filter at its input.

The last schematic you posted shows current-limiting resistors for all the LEDs. The datasheet for the LM3915 explains why they are not necessary: The IC Limits The Currents. The rectifier diode at its input spoils its action at low levels. An active peak detector circuit using an opamp should be used instead that is shown in the datasheet. Its VR1 adjusts how much signal level lights how many LEDs.

Here is how to convert stereo into mono:
 

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audioguru

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Double post deleted because the old AC-DC "You shook Me All Night Long" song caused goose-bumps.:eek:
 

Electrophile07

New Member
Ok thanks.... I will try your circuit as well as the one above and check which one suits me the best.... Also what would happen if I do the stereo to mono conversion and apply it to the input of the circuit directly without using any amplifier? It would still work right? The only Opamp I've worked with is IC741 so if there is any quick fix I can use that would be great :D

4pyros - yeah I think I could possible do that but then again who likes one sided music? :p Ive heard quite a few songs in which the beat plays in the left ear and the rest of it comes thorough the right...

Audioguru - I heard that song for the first time and loved it! The only ACDC song I'd heard uptill now was Big Gun
 

audioguru

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What would happen if I do the stereo to mono conversion and apply it to the input of the circuit directly without using any amplifier? It would still work right?
The sensitivity of the circuit is extremely sensitive when VR1 is turned down because then a tiny signal level will light all the LEDs. Then an amplifier is not necessary. But the diode blocks low level signals.

The only Opamp I've worked with is IC741.
The lousy old 741 opamp was designed 46 years ago. There are thousands of much better opamps today that simply plug in where a 741 was.

Audioguru - I heard that song for the first time and loved it!
I heard it in 1980 (when my daughter was 1 years old, before my son was born and before I got "fixed") and I heard it every year up to now.
 

4pyros

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Ive heard quite a few songs in which the beat plays in the left ear and the rest of it comes thorough the right...
Then use the left side.
Also what would happen if I do the stereo to mono conversion and apply it to the input of the circuit directly without using any amplifier? It would still work right?
Yes you should need an op amp at earphone levels, only if you tried to us a mic.
Audioguru - I heard that song for the first time and loved it! The only ACDC song I'd heard uptill now was Big Gun
I have seen them live when I was a Teenager.
 

Electrophile07

New Member
Ok, so I've been to the electronics hardware store and have bought the necessary components for the circuit below (posted earlier).
He has given me this audio jack which is a 2 ended 3.5mm jack. So basically(correct me if I am wrong) what I have to do is insert one end into my phone/ mp3 player and about the other end, Ill have to cut the wire in between to obtain the 2 wires inside and make the stereo to mono conversion and apply it at the place marked audio input...
 

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4pyros

Well-Known Member
Most Helpful Member
Ok, so I've been to the electronics hardware store and have bought the necessary components for the circuit below (posted earlier).
He has given me this audio jack which is a 2 ended 3.5mm jack. So basically(correct me if I am wrong) what I have to do is insert one end into my phone/ mp3 player and about the other end, Ill have to cut the wire in between to obtain the 2 wires inside and make the stereo to mono conversion and apply it at the place marked audio input...
Just use the left side if you want to make it easier.
 

audioguru

Well-Known Member
Most Helpful Member
If you want to display EVERYTHING that is in stereo converted to mono then the new cable has one end cut off and its two audio wires connect to the two resistors that make the converter. The shield wire must connect to 0V of the VU meter circuit. The free ends of the two resistors are connected together at the input of the VU meter circuit.
 
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