Vu meter, questions

Thompeb · 21st July 2011, 08:32 PM

Hi!

Im new to lm391x
Im planing to build several vu meters for cubase music studio.
I want the output from a midi source to go in to the input of an lm3915 and lm3916 extended range meter
My question to u people. can the input come from a dc source or do I need ac.

And is it possible to change the input to 3,12v for full scale instead of 7,8v

Cant find the documents in swedish. hard to the english terms.

thanks
/Thomas

mnemneth · 22nd July 2011, 08:45 AM

Hi Thomas,
the LM391x chips are happy with DC or AC. The internal comparitors switch at DC levels, so no problem, there.

Sandy

Thompeb · 22nd July 2011, 09:38 PM

Hi!

Thanks sandy!

Now i have to ask one more thing. The T1 transformer. what kind do i need, can i make it my own or can i find it on ebay for good price.

Thomas

Tajzmaj · 22nd July 2011, 09:54 PM

It depends in which mode you will use meter. Bar or dot........but for an example if there you have 20 leds and each draw 20mA you will need some 0.5A of current. If you want to build several meters it is good idea to make one pwr supply for all. Some 7-10VDC will work and chips will run cool....
Regards, Taj

jaycee · 23rd July 2011, 01:23 AM

You could also use any pre-made 12V supply that supplies enough current.

Changing the input voltage scale would simply be done with a potential divider. This is actually what the second IC has on it, with R3/R4.

Thompeb · 23rd July 2011, 08:57 AM

Ok. I understand.

Im planing to build 26 vu meters in bar mode. on three pcb´s 8, 8, and 10 on the last one.
494 leds. So then i can use a transformer from 230v ac to 6.3v ac or do i need more.

More questions

1n4001 do i have to change the value on them and the 2.2uf?

The formel. R3/R3+R4= 0.158= - 16 db. Is it 158 ohm?

Thomas

Tajzmaj · 23rd July 2011, 12:04 PM

On my experience some 7-10 Vac is batter if you want to build some regulated psu. You will have some problems if you use just simple gretz and capacitor psu because cap voltage will drop when all vu meters will go to full scale.....so regulated psu is needed......
uf I barely see what I'm typing. I'm sitting at the sea shore.......and sun is very bright....
Best regards, Taj

Thompeb · 15th August 2011, 03:28 PM

Sounds nice with the sea and sun.

I will do as u say tajzmaj, 7-10volt ac maybe 12v. without capacitor?
But do I need resistors for the leds, cant find it out in the paper.
I have a lot of them wich works good with 12v, if i need em maybe better to drive them by 12v insteed.

regards, Thomas

21st July 2011, 08:32 PM	#1
Thompeb diyAudio Member Join Date: Jul 2011	Vu meter, questions Hi! Im new to lm391x Im planing to build several vu meters for cubase music studio. I want the output from a midi source to go in to the input of an lm3915 and lm3916 extended range meter My question to u people. can the input come from a dc source or do I need ac. And is it possible to change the input to 3,12v for full scale instead of 7,8v Cant find the documents in swedish. hard to the english terms. thanks /Thomas

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22nd July 2011, 08:45 AM	#2
mnemneth diyAudio Member Join Date: Feb 2006 Location: Dundee	Hi Thomas, the LM391x chips are happy with DC or AC. The internal comparitors switch at DC levels, so no problem, there. Sandy

22nd July 2011, 09:38 PM	#3
Thompeb diyAudio Member Join Date: Jul 2011	Hi! Thanks sandy! Now i have to ask one more thing. The T1 transformer. what kind do i need, can i make it my own or can i find it on ebay for good price. Thomas

22nd July 2011, 09:54 PM	#4
Tajzmaj diyAudio Member Join Date: Mar 2011 Location: Ljubljana	It depends in which mode you will use meter. Bar or dot........but for an example if there you have 20 leds and each draw 20mA you will need some 0.5A of current. If you want to build several meters it is good idea to make one pwr supply for all. Some 7-10VDC will work and chips will run cool.... Regards, Taj

23rd July 2011, 01:23 AM	#5
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	You could also use any pre-made 12V supply that supplies enough current. Changing the input voltage scale would simply be done with a potential divider. This is actually what the second IC has on it, with R3/R4.

23rd July 2011, 08:57 AM	#6
Thompeb diyAudio Member Join Date: Jul 2011	Ok. I understand. Im planing to build 26 vu meters in bar mode. on three pcb´s 8, 8, and 10 on the last one. 494 leds. So then i can use a transformer from 230v ac to 6.3v ac or do i need more. More questions 1n4001 do i have to change the value on them and the 2.2uf? The formel. R3/R3+R4= 0.158= - 16 db. Is it 158 ohm? Thomas

23rd July 2011, 12:04 PM	#7
Tajzmaj diyAudio Member Join Date: Mar 2011 Location: Ljubljana	On my experience some 7-10 Vac is batter if you want to build some regulated psu. You will have some problems if you use just simple gretz and capacitor psu because cap voltage will drop when all vu meters will go to full scale.....so regulated psu is needed...... uf I barely see what I'm typing. I'm sitting at the sea shore.......and sun is very bright.... Best regards, Taj

15th August 2011, 03:28 PM	#8
Thompeb diyAudio Member Join Date: Jul 2011	Sounds nice with the sea and sun. I will do as u say tajzmaj, 7-10volt ac maybe 12v. without capacitor? But do I need resistors for the leds, cant find it out in the paper. I have a lot of them wich works good with 12v, if i need em maybe better to drive them by 12v insteed. regards, Thomas

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