lm 3915 vu meter problem.

[Mooly]

The one marked R2 in that circuit will just alter the brightness (according to the data sheet) and so you can just use a fixed value somewhere around say 4k7 as a test.

You need your shiny new meter to be able to do all this properly

 

[lukutis]

if that additional valubale resistor will control brightness so what that old (first) one gonna do? nothing?

 

[Mooly]

It altered the sensitivity by altering the reference voltage.

 

[turk 182]

lukutis
sorry don't have the data sheet in front of me but isn't maximum sensitivity achieved when pin 8 see's a direct connection to ground?
any offset from ground would change the meters sensitivity (meaning it takes more input signal to drive the meter to full scale)

 

[Mooly]

That's how I understood it too.

http://www.diyaudio.com/forums/everything-else/267760-lm-3915-vu-meter-problem.html#post4227292

 

[blu_glo]

Folks, what does this bit mean exactly.

"I use 9V power source
3,5V , 0,02A 10leds"

The way I see it you're not getting enough current to drive all the leds? I would suggest the LED supply should be capable of at least 200mA (or 10x LED current) and more if the bargraph chip and preceeding opamp circuit are using same supply....

 

[blu_glo]

I didn't see any answer to #56 - the use of a dropper resistor in series with the LEDs supply is dubious but the '3915 data sheet does recommend a 7.5ohm in series with the LEDs and 2.2 uF Tantalum (could also be electrolytic) from junction of LEDs/series resistorto pin 2 (0V). personally, if i found I had dissipation problem, I'd use a 78M05 (5V, 500mA regulator) for the LED supplies.

 

[Mooly]

The outputs are current sinks and so any series resistor correctly chosen will not alter the brightness but simply reduce the overhead on the sinks.

 

[blu_glo]

Yes, it will help to a point, but if he uses resistor designed for 5 LEDs on a design with 10, his resistor may end up dropping too much for the LEDs to light at all?

 

[turk 182]

i hope lukutis is getting all this...

 

[Mooly]

Lol, I wonder

Yes, the resistor would have to be chosen to allow all LED's to draw the design current. Keep increasing the value until the current with all 10 LED's lit falls a little, then drop the value back.

 

[lukutis]

what u mean guys? what resistor are u talking about right now? the valuable ones or nope?

 

[turk 182]

can you upload pic's of what you have wired up?
get a multimeter yet?
sorry don't know what your question is about the resistors is (did you mean - "variable" as in a "potentiometer" ?) cuz nobody says they have to be expensive?!!
are you still unclear as to how this circuit works ?

and what are you using to power this circuit ?

 

[blu_glo]

the resistor you may have put in series with the LEDs, did you put one? If so, what value? See my post # 107....

 

[lukutis]

to power up this circuit i use 9V battery. and in my circuit there is only one resistor which is connected from pin 7 to pin 8 and value of this resistor is 1k Ohms. I havent got multimeter yet;/

 

[turk 182]

well if you look at some of the diagrams the supply voltage for the LM3915 is listed as: 12 to 20 Vdc your already 3 volts below minimum and if you've run this on the same battery for a while... i hope you have "fresh" spare's available.

anybody want to spearhead doing some crowdfunding so we can get lukutis a multimeter

if you have a 1k from seven to eight but neither are referenced to ground i'd be at a loss to explain how your getting any display...

 

[lukutis]

resistor 7 connects to 8 and 8 pin connects to negative.. so i guess that okay then? Yes i saw in some circuits that people use 12Vdc but man.... i dont have any idea how do i run a circuit with 12V . I saw some videos where people build their transformer for 12V but that seems like a hard task for me

 

[turk 182]

if your planning on playing with electronic circuits a homebrew 12 volt supply is almost essential but then i am talking to someone who doesn't own a meter...

crowdfunding anyone....

 

[lukutis]

okay.. Can u suggest how do i make or how do i get the simpliest choose of 12V? :dD

 

[turk 182]

don't know where you live or what's available to you and considering you don't own a multimeter it not a project i'd recommend for a beginner like yourself.

the lm 3915 can run up to 20vdc why don't you series two 9v batteries =18v