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Need help about VU meter

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afen_ho

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hello,

I want to ask about my Vu meter where i connect it to my car audio.
the VU meter is work , but the sound have a noise ( noise like a radio have no signal) , and then i disconnect the VU meter, the sound comes normally. what happened with my vu meter.


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youtube : https://www.youtube.com/user/afenho?feature=mhw5#p/a/u/0/_YM3Vg0aGsc

i have tried to use LM7812 to make the voltage stable, but has no change ( still noisy ) .

somebody can help me to fix it.
thanks
 
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Before I forget you can't use a LM7812 in an automotive application. The 7812 has about a 2 volt dropout voltage so it requires a minimum of 14 volts in to get 12 out.

Next, are you sure you want to get the amplifier output to the speakers? You may want to get the audio in to the VU meter from the input to the amp.

Ron
 
Does the noise happen when only the power is connected, or when the audio inputs are connected?
 
Most 15W into 4 ohms car amplifiers are bridged with speaker signals on both speaker wires. If you connected the input and ground wires of your VU meter to a speaker then the ground wire is shorting the output of one amplifier which might cause smoke and a noise.

If the amplifier still works after being shorted then try connecting only the input wire of the voltmeter to one speaker wire.
 
Before I forget you can't use a LM7812 in an automotive application. The 7812 has about a 2 volt dropout voltage so it requires a minimum of 14 volts in to get 12 out.

Next, are you sure you want to get the amplifier output to the speakers? You may want to get the audio in to the VU meter from the input to the amp.

Ron

the VU meter is running between 6 - 12 V, so i think it's no problem if the LM7812 is droop 2V ( Correct me if i'm wrong).
ok, i wiil try to connect audio input from the vu meter to the audio input amp ( use RCA audio jack).

thanks for the reply..
 
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Most 15W into 4 ohms car amplifiers are bridged with speaker signals on both speaker wires. If you connected the input and ground wires of your VU meter to a speaker then the ground wire is shorting the output of one amplifier which might cause smoke and a noise.

If the amplifier still works after being shorted then try connecting only the input wire of the voltmeter to one speaker wire.

ok , i will try use 1 wire .

thanks for reply..
 
I think that duck guy is right - I see your circuit has one input grounded, the car audio speaker outputs are probably bridged, so you were shorting out one side.
 
Yeah, I also think the "duck guy" is correct in his assumption. :)

Ron
 
If the amplifier still works after being shorted then try connecting only the input wire of the voltmeter to one speaker wire.

ok , i will try use 1 wire .

thanks for reply..[/quote]



i have tried use 1 wire to connect input signal to spk out AMP, the sound is clear ( no noise), but the LED light become not bright.
 
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i have tried use 1 wire to connect input signal to spk out AMP, the sound is clear ( no noise), but the LED light become not bright.
Maybe you connected the input of the VU meter to the damaged (because it was shorted) amplifier speaker wire. Try connecting to a different amplifier speaker wire.

Can you post a schematic of the LM3915 circuit?
 
Also, it is common for bridged automotive audio amps to have DC of ~7V riding on the speaker wires. A DC blocking capacitor in series with the VU audio input might help.
 
Your kit has two inputs. Only one input is used. You forgot to say which input you used.
The inputs do not have a series input coupling capacitor so the circuit will display DC. If your amplifier is bridged then each speaker wire has DC which will cause a display even if the amplifier is not playing sounds.

The input with the diode is a peak detector so each LED will light fairly brightly with the same brightness.
The input without the diode shows instantaneous levels which will be fairly dim. The highest levels will light the higher LEDs very dimly.

Get a multimeter (some cost only $10.00) and measure the DC voltage at both wires of a speaker and post them with your reply here.
 
input 1 is dot mode
input 2 is bar mode.

i use use both of these input, where i added a switch selector to choose dot mode ( input 1) or bar mode (input 2).
 
input 1 is dot mode
input 2 is bar mode.

i use use both of these input, where i added a switch selector to choose dot mode ( input 1) or bar mode (input 2).
No. Pin 9 selects DOT or BAR mode. Read ther datasheet.

Input 1 is an averaging detector. It shows momentary instantaneous levels. If pin 9 is set to BAR mode then the display is a dim blur. If pin 9 is set to DOT mode then peak and average levels can be seen.

Input 2 is a simple peak detector. If pin 9 is set to DOT or BAR mode then peak levels will be bright on the display.

My VU meter has a better peak detector (and it doesn't use an averaging detector) and its pin 9 is usually set to BAR mode.
 
the VU meter is running between 6 - 12 V, so i think it's no problem if the LM7812 is droop 2V ( Correct me if i'm wrong).
ok, i wiil try to connect audio input from the vu meter to the audio input amp ( use RCA audio jack).

thanks for the reply..

no, you misunderstand.
The 7812 needs a minimum of 14V into it to produce a stable 12V out of it. anything less than 14V and its not going to give you a regulated voltage out

Dave
 
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