lm3915 vu meter problem

[lukutis222]

Hello everyone. So i started learning about electronics slowly, my physics knowledge is really bad but i hope i can fix that.
This is my second electronics project so i decided to do something cool... https://www.electro-tech-online.com/imgcache/8472-14.gif
I end up doing this, i have no idea how it works and i barely connected everything to my breadboard.
I use 9V power source
3,5V , 0,02A 10leds
10k potenciometer
and 1k(didint have 1,2k) resistor exactly as shown in the scheme.
everything seemed to work fine but when i play music only 5 or 6 leds are glowing and the last 4 are not doing anything ;/ Whats should be wrong?
I tryed to read lm3915 description but there is so much information my head almost blew up :/ there is no way i can understand something with brains like mine, so i hope u got some simple explanation how to fix that

 

[FvM]

The full scale input level (Vpeak) is adjustable between 1.2 and about 12V with the 10 k var resistor. Typically you would set it to zero for reasonable sensitivity. Did you try? I guess you are operating the VU meter with 12 V range.

 

[Audioguru]

The 10k pot is shown connected as a variable resistor from 0 ohms to 10k ohms, When it is 0 ohms then the 10th LED will light when the input is 1.25V which is a loud line level signal. When the pot is set for 10k ohms then the 10th LED lights when the input is 12V which is much louder than line level and is an amplifier output of 9W into an 8 ohm speaker.

The datasheet shows and recommends using one of the peak detector circuits shown. Without having a peak detector then the LEDs are a dim blur with the brightest at the average level of the input signal.

 

[lukutis222]

Yeah i tryed to play with my pot but if i set my pot to 10 barely 2 or 3 leds are glowing and then i maximum 5-6 leds goes on. And one more interesting thing. My resistor of 10k Ohms is connected to pin 7 and other side to pin 8. When i connect pin 6 to pin 8 with a resistor all my leds starts to glow but not correctly.. First leed is very bright and the other 4 is medium bright.. 6th is very bright and the other 4 is medium bright...
Btw i dont know what is peak detector. Is there any way that my 3,5V LEDS are have too high voltage? maybe if i swap them with 2V that might work?

 

[FvM]

Regarding LED voltage, the circuit will be fine with 3.5V LEDs if the supply is >= 5V.

You should try with the basic circuit as giving in the link or the LM3915 datasheet, R1 = 1 or 1.2k, R2 = 0 for maximum sensitivity.

Audioguru was referring to the peak-detector circuits in the datasheet, Fig. 1 and Fig. 4. He explained very clearly why he suggests a peak detector. The problem of not all LEDs lighting isn't however related to using a peak detector or not.

 

[Audioguru]

Yeah i tryed to play with my pot but if i set my pot to 10 barely 2 or 3 leds are glowing and then i maximum 5-6 leds goes on.

That is what the pot is for, it adjusts the sensitivity. But when the pot is 0 ohms and the sensitivity is the highest then all the LEDs do not glow because the level of your sound source is too low and needs to be amplified.

And one more interesting thing. My resistor of 10k Ohms is connected to pin 7 and other side to pin 8.

No, you do not have a 10k resistor. You said earlier that you have a 1k resistor between pin 7 and pin 8 which is fine.

When i connect pin 6 to pin 8 with a resistor all my leds starts to glow but not correctly.. First leed is very bright and the other 4 is medium bright.. 6th is very bright and the other 4 is medium bright...
Btw i dont know what is peak detector. Is there any way that my 3,5V LEDS are have too high voltage? maybe if i swap them with 2V that might work?

A resistor from pin 6 to pin 8 will be parallel to your 1k resistor and will produce a lower resistance which changes the input level required to light the LEDs.
Your LEDs have different sensitivities because you do not have a peak detector. There are a few peak detector circuit shown and described in the LM3915 datasheet. Why don't you read the datasheet?
The datasheet describes that the outputs regulate the current in the LEDs so a 2V LED and a 3.5V LED will both have the same amount of current.

 

[lukutis222]

Yeah i meant 1 k resistor. And about the datasheet.. My english is not so good and i have lack of information about physcis... Most of the letters and information is just too much for me... Is there any way to easy amplify my sound source?

 

[Audioguru]

Is there any way to easy amplify my sound source?

An opamp is the easiest way to amplify audio.

I used a dual opamp to amplify and make a peak detector for my LM3915 circuit:

 

[lukutis222]

hmmm i havent heard about opamp. I checked google quick i find out that its something like this? http://www.silisyum.net/pic/opamp/opamp2.jpg?
i can buy some parts and try play with that? but i need circuit how to connect evertyhing.. i think its enough single opamp im not even sure if i can do it..

 

[FvM]

There's a simple peak detector circuit shown in Fig. 1.

But as suggested before, why don't you try first without a peak detector, just adjusting the sensitivity to sour audio signal?

 

[lukutis222]

What u mean Fig.1? where?
and what u mean adjusting sensivity? I tryed to adjust my pot all the way down and all the way up. Is there anything more i can do ?

 

[FvM]

Sorry, I'm having an old datasheet. It's Fig. 17 in the recent Rev.C from TI.com

The assumption was so far that 1.2V peak can be achieved by a standard audio (line) signal. Otherwise a preamplifier should be used, or a voltage divider betwen pin 7 and pin 6 to further reduce the full-scale level.

 

[Audioguru]

TI's datasheet for the LM3915 says that the simple peak detector shown in figure 17 should be used when the input has a peak level of 10V (been there, done that).
Consumer audio products frequently have a line level of only a few hundred mV then the top 4 LEDs will never light when the LM3915 is set for its maximum sensitivity of 1.2V full scale. The 3 or 4 LEDs below them will be extremely dim without having a peak detector.

My LM3915 sound level indicator circuit uses a microphone as its input and automatically switches ranges for an additional 20dB of range so it always shows very low to very loud levels. Of course it has a peak detector so that all LEDs light brightly.

I suggest that the OP purchase a kit of a VU meter (Velleman?) since he has problems with English and theory.