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Author Topic: Problem with audio jack and psu alimetation  (Read 2614 times)

bogdan_lupuro

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Problem with audio jack and psu alimetation
« on: April 20, 2006, 10:48:48 AM »

Hello everyone

I have a problem. I made a vu-meter wich works perfect when powered from a battery and with the PC audio signal. But when i connect it to the PC PSU it doesn't work anymore. I've noticed that it make mass beetween the jack's top and PC case.

Is there any possibility to avoid this, except powering it from a battery ?

Thanks

Bogdan
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Skylined

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Re: Problem with audio jack and psu alimetation
« Reply #1 on: April 20, 2006, 11:15:19 AM »

A schematic or a drawing of what you're trying to do would come in handy to help you. ;)
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bogdan_lupuro

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Re: Problem with audio jack and psu alimetation
« Reply #2 on: April 20, 2006, 11:23:44 AM »

Here is the schematic.

Like i said it all works perfect until i connect it to the computer psu, and i saw  that the top of jack connects to the computer case

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viridius

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Re: Problem with audio jack and psu alimetation
« Reply #3 on: April 21, 2006, 06:47:19 PM »

What do you mean it "make mass between the jack's top and PC case"?  Your power could be dirty; did you try connecting a bypass cap across the power pins?
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Nate53085

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Re: Problem with audio jack and psu alimetation
« Reply #4 on: April 22, 2006, 12:26:00 AM »

Agreed about the bypass cap.

But also, looking at how your LEDS are wired, your sinking current into the chip.  Your rail says 12 to 20 volts... and there are no limiting resistors.  I know nothing about that chip and am sorta lazy right now... but could it be that the reason that it is working with a battery is that the battery isn't sourcing enough current to really do to the circuit what you ask (put 12 to 20 V across an led)?  What voltage are your batteries, what voltage are you powering it with, what current are you getting, what current do you need?
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bogdan_lupuro

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Re: Problem with audio jack and psu alimetation
« Reply #5 on: April 22, 2006, 02:02:07 AM »

Viridiues yes looks like that sentence is lost in translation :). Well i mean that the top of the jack makes ground with the case and power cables from PSU. not sure if this is corect also. Bascaly I tooked a multimeter and check if the signal cable makes any connection with the case and it makes. if i remove the psu cables it doesn't make a connection anymore.

The top of the jack somehow has a link with the computer case and with the power cables .

I tryed puting a capacitor on one signal source (as how someone telled me), tryed on both. Then someone telled me to put a capacitor on both signal wires (SIG and Rlo ). And if i do this the leds stay up all the time, they don't play by the music.

What i've done was : I've cut the wires and puted capacitors on them, in series.  One capacitor is 0,033 micro and the other is 1 micro both at 250 volts. Is there any problem with what i have done ?

Should i place the capacitor on the power cables? And if so how? on both wires or on only one ?

The battery i was testing was a 9V, but also tested with 12 V. So i don't think it is from this.

BTW thi is the datasheet of the LM3915 http://www.bogdesigns.com/LM3915.pdf

Bogdan
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viridius

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Re: Problem with audio jack and psu alimetation
« Reply #6 on: April 22, 2006, 06:12:57 PM »

The cap should go between the Vdd and Vss pins on the chip.  That chip does its own current limiting for the LEDs, so external resistors shouldn't be necessary.
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bogdan_lupuro

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Re: Problem with audio jack and psu alimetation
« Reply #7 on: April 23, 2006, 02:28:58 AM »

Thanks viridius. You mean between V+ and V- ,right? That means i can put it on the PSu wires too? because it is hard for me to get to the circuit now.

Bogdan
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Re: Problem with audio jack and psu alimetation
« Reply #8 on: April 23, 2006, 02:51:21 PM »

VDD = + = Positive
VSS = - = Ground

The cap has to be as close to that circuit as possible.
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bogdan_lupuro

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Re: Problem with audio jack and psu alimetation
« Reply #9 on: April 24, 2006, 08:59:56 AM »

Thanks i'll try and let you know

Bogdan
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