Help with this Spectrum analyzer schematic PLEASE

Discussion in 'The Projects Forum' started by dyeraaron, Jan 6, 2010.

  1. dyeraaron

    Thread Starter Active Member

    Oct 27, 2008
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    0
    Hi all,

    Sgt. Wookie has been helping me a little...I just don't know where to go now.....Ok...so I have 10 Band pass filters built on a bread board...which are in this schematic as well....I have a 4017 Counter to supply my highs for the 10 x 10 LED matrix I've got the spectrum analyzer built for....Instaed of the inverters or Nand gates as Ive seen in some schematics..I've got a 555 clocking my 4017...I have either 3914 or 3915s I can use to produce my lows for the Leds......I'm just stumped how do I tie the output signals from the Bandpass filters into the 3914 / 3915....if you look at this schematic ( scroll through) you'll see how each filter is for a band certain frequency but then it ties them all into series running into pin 5 ( which is the input pin ) for the 3914......Should I just use fewer filters ??? I don't have 10 3914 / 3915s so I can t use a single chip for each filter....Please anyone help...I can't or don't have any access to PICS...If you have any information for me I'd deeply appreciate it....this is the link for the schematic
    http://www.scribd.com/doc/12903797/Audio-Spectrum-Analyzer-Circuit-Desgin-Project
     
  2. dyeraaron

    Thread Starter Active Member

    Oct 27, 2008
    57
    0
    Just wanted to put this back at top hoping someone could help me
     
  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The transistor switches are also selected by the CD4017 and pass the outputs of the filters to the input of the LM3915 one-at-a-time. This is called "multiplexing".
    Since only one filter lights its LEDs at a time then its LED indication is turned on for only 1/10th of the total time and will appear at 1/10th the normal brightness. It results in a very dim display.

    The display can be made brighter if the outputs of the LM3915 are boosted 10 times with transistors and if the transistors at the outputs of the CD4017 have their currents increased 10 times.
     
  4. dyeraaron

    Thread Starter Active Member

    Oct 27, 2008
    57
    0
    I thought the 3915 Puts out lows for the Cathode of the LEDS.....How would a low intensify the brightness? Also which Type of transistor shoulf I use for the outputs of the 4017...PNPs or NPNs I have both.......with the Transistor switches that'll pass the frequencies the filters put out..I have C1815's audio transistors.....so what you're saying is the schematic portion of the filtering is right????? could you look at the page where the 4017 and 3914 are......and tell me why they have inverters set up for the outputs of the 4017.....I thought they were high to begin with why would you want the anode side of the LEDs to become low when the 3915 is producing lows for the cathodes????
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Yes, but not enough current for the multiplexed LEDs to be bright.

    The anodes of the LEDs must be pulled up by PNP transistor that inverts, so a logic inverter drives them from the output of the CD4017.

    The original Vietnamese schematic is correct but the LEDs are very dim.

    I told you that the anodes of the LEDs must be pulled high but the output current of the CD4017 is not high enough so a logic inverter drives a PNP transistor to provide still not enough current.

    The output of the CD4017 goes high but with a low current.
    Then the logic inverter output goes low.
    Then the output of the PNP transistor pulls up the anode of its LED when its input goes low.
     
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