Light Organ not responding to Input

Discussion in 'The Projects Forum' started by kreiff, Oct 28, 2013.

  1. kreiff

    Thread Starter New Member

    Oct 28, 2013
    2
    0
    Hi All!

    I'm working on a light organ project that I found through Collin Cunningham YouTube channel. You can find the youtube video about the project here:
    http://www.youtube.com/watch?v=ubQC839Pvqk

    I purchased the kit for the project from Jameco. You can see the kit instructions here:
    http://www.jameco.com/Jameco/workshop/diy/ledcolororgan.html

    and a parts list here:
    http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2126272_-1

    You can see the schematic for the project here:
    http://www.jameco.com/Jameco/workshop/diy/basicledcolororgan-fig11.jpg

    I've essentially finished all of my soldering and I've hooked the board up to a 12v DC power source and the LEDs will initially flicker on when I do this, but when I plug in my ipod (or any music source) just the blue and yellow LEDs will flash together about every second or so, but the lights do not react to the music playing.

    When I hook the board up to a y-connector to play music into the board and a speaker simultaneously the board actually seems to be emitting it's own sound that is picked up by the speaker and sounds like a distorted bass drum sound.

    The one part of the schematic that I was unsure about is the connection from the 100k resistor to the VCC when it comes out of the 3 pin in the MC34072P. I wasn't sure if the VCC was meant to be just the power source or potentially another connection. In the end, I just connected it to power, but this could potentially be a mistake on my part.

    I am also fairly new to soldering, so it's possible that some of my joints could be shorting, but I'm not sure where.

    I've taken pictures of the top and bottom of the completed project:

    Top:
    [​IMG]

    Bottom:
    [​IMG]

    Any help with finding my error or at least pointing out the most suspect soldering joints would be really helpful. I'd love to get this project fully working.

    Thanks!

    -Kyle
     
  2. JohnInTX

    Moderator

    Jun 26, 2012
    2,341
    1,024
    I'm not sure what you mean by that. Wire the 34072 like the schematic. The two 100K R27,R28 from Vcc-GND form a voltage divider filtered by C15. Pin 3 is connected to this node which is at 1/2 Vcc. The amplifier is connected as a buffer driving GNDDIGITAL to 1/2Vcc. This puts the reference point for the active filters at 1/2Vcc so that the AC audio wave can swing +/- around it.

    Sorry, I can't tell what you have wired but that's what it should be. I don't know what the U2.1 ref on the amplifier is (probably a schematic capture identifier) but all of the pins of the 8 pin DIP package are accounted for so I think you can ignore it.

    On the 33204, make sure that pin 4 = 12Vcc, 11 = GND (battery ground) and that pins 3,5,10 and 12 are about 6V (GNDDIGITAL). All other grounds look like they are GND i.e. battery ground.

    Check it out and be sure that GNDDIGITAL is 1/2 the Vcc voltage.

    Good luck!

    BTW: If you google 'tone generator download' you'll get stuff that will play tones at various frequencies from your PC. Use something like that to ring out the filters. There are probably any number of phone apps that make tones as well.

    EDIT: Looked at the video and most of this is covered. Grr. Poke around to see what the voltages are..
     
    Last edited: Oct 28, 2013
  3. kreiff

    Thread Starter New Member

    Oct 28, 2013
    2
    0
    @ JohnInTX

    Thanks for you response. I know that most of this is covered in the video, conceptually, but I'm honestly quite new to this, so I don't have a perfect handle on schematics.

    From your response, I do think that I've got the R27 connected incorrectly, but I'll also use a voltage meter and poke around the circuit and make sure that everything is in the correct range.

    Thanks again!
     
  4. Sharkymc

    New Member

    Nov 30, 2014
    3
    0
    Hey I'm at the same spot and wondering if you figured out where the v+ or Vcc goes? Sort of holding off power and the puff of smoke potential since it's the first one like this I'm trying out :)
     
  5. Sharkymc

    New Member

    Nov 30, 2014
    3
    0
    Sounds like it is connected to 12v and the resistor / op amp splits the voltage? Pretty new to the virtual ground op amp idea
     
  6. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    If nobody else said, make sure your LED's aren't connected backwards. If nothing else works, you can try to disconnect the network to the right of C9 and connect it to the node to the right of C14, or else make up another network identical to the one I've suggested you connect to. If your LED's light up, at least you know everything to the left of C14 is good. If not, play with your network and you might find something wrong which you can correct. You should be able to just connect an LED and series 470 ohm resistor directly to the output of U1.1 and see something.
     
  7. Sharkymc

    New Member

    Nov 30, 2014
    3
    0
    hey thanks for the idea, i connected the node by c9 to the right on c14 and getting the same blinky then nothing so I'm back at thinking about the Vcc note. I've tested the leds straight off a battery and they work ok. so it looks like i'm down to checking through the path.



    note sure i can do the last test like you said by passing the diode, had my eng. friend stressing how the diode protects that part from direct 12v.
     
  8. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Use a regular diode across the LED, connected diode-anode to LED-cathode and diode-cathode to LED anode, also called anti-parallel.
     
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