lm3915 vu meter problem

Discussion in 'General Electronics Chat' started by lukasxx1, Jan 9, 2015.

  1. lukasxx1

    Thread Starter New Member

    Jan 9, 2015
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    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... http://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 :)
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The problem may not lie with the 3915. The signal peaks may not be strong enough, or last long enough, to light all the LEDs.
    Does your circuit include a peak detector stage?
     
  3. lukasxx1

    Thread Starter New Member

    Jan 9, 2015
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    nope
     
  4. Alec_t

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    Sep 17, 2013
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    What is the signal source you are using to drive the 3915?
     
  5. lukasxx1

    Thread Starter New Member

    Jan 9, 2015
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    Im not sure how to explain that and im not even sure what are u asking me. But i connected all my circuit to 3,5mm jack and connected to my pc
     
  6. Alec_t

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    Sep 17, 2013
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    So, the PC sound card is the signal source. Depending on the card make and the audio you are playing, the output from the card may only be a Volt or so peak-to-peak. If the 10k pot is adjusted correctly and the battery is fresh you should be able to get all LEDs to turn on, albeit faintly and with some flicker.
    Have you set the PC to give maximum output level?
    Have you adjusted the pot for maximum sensitivity (= minimum resistance)?
    With R1 = 1k the current per LED should be about 12mA. If all LEDs were 'on' the total current required from the 9V battery (which I assume is a little PP3 type) would be 120mA. If the battery is weak, attempting to draw that much current may drop the supply voltage to the circuit enough to prevent all LEDs turning on.
     
  7. lukasxx1

    Thread Starter New Member

    Jan 9, 2015
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    Yes my battery is pp3 and its pretty fresh. How did u calculate that the each led will get 12mA? and how do i set my pc to give maximum output levle?
     
  8. GopherT

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    Nov 23, 2012
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    If your PC is only giving a volt or so of output, maybe even only 0.3v, then you need to look at your R(Hi) pin (pin 6). This tells the chip what the highest voltage to expect. Adjust R1 and R2 to appropriate values - if you keep your R1 value the same, make R2 smaller (per TI datasheet figure 23).
    http://www.ti.com/lit/ds/symlink/lm3915.pdf
     
  9. lukasxx1

    Thread Starter New Member

    Jan 9, 2015
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    so in this case i dont even need potenciometer? just a bunch of resistor? why is that resistor has arrow across it?
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You could try to use a potentiometer of 100K between pin 6 and pin 7 of the LM3915, to make it more sensitive.
    The existing pot of 10K on pin 8 can be set on minimal value.

    Bertus
     
  11. lukasxx1

    Thread Starter New Member

    Jan 9, 2015
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    okay so how exactly i connect this potenciometer? one leg to 6 other to pin 7 and the middle leg?
     
  12. bertus

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    Apr 5, 2008
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    Hello,

    The middle leg to one of the others, just like the 10K potentiometer.

    Bertus
     
  13. lukasxx1

    Thread Starter New Member

    Jan 9, 2015
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    my 10k potenciometer one leg goes to pin 8 and other to ground . so u want me to put 100k somewhere and connect one leg to 6 and other leg to 7 and middle leg to which one? that one which goes to 6 or 7?
     
  14. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Here I have drawn the pot onto a schematic from the datasheet:

    [​IMG]

    Bertus
     
  15. lukasxx1

    Thread Starter New Member

    Jan 9, 2015
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    holy crap bro im afraid im not ready for this scheme yet. I have no idea what is this triangle and stuff. But i understood where this potenciometer goes:) Would it work if i connect this potenciometer on my scheme?
     
  16. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I read the datasheet, regarding R1 :).
    If you're running Windows you probably have a little loudspeaker icon in the system tray at the bottom right corner of the screen. Right-click on that.
     
  17. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    E
    Everything inside the dotted lines in the image in Bertus's post is the inner workings of the LM3915. Already done for you. The numbers next to each wire leaving the dotted line area are the PIN numbers of the LM3915 chip. You only have to worry about the resistors and LEDs outside of the dotted line rectangle.

    Note that he added the potentiometer to the left edge of the drawing as a 100k pot.
     
  18. lukasxx1

    Thread Starter New Member

    Jan 9, 2015
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    Ohh i understood. Thaaanks il try that
     
    Last edited: Jan 10, 2015
  19. bertus

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    Apr 5, 2008
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    Hello,

    Inside the dotted line is the internal schematic of the LM-chip.
    The triangles are the comparators that will compare the input voltage with the reference voltages and set the led on or off.

    Bertus
     
  20. lukasxx1

    Thread Starter New Member

    Jan 9, 2015
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    So i dont even need my 10k pot? cuz i cant see that in this circuit? or should i just add one more pot
     
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