Midi fighter mod question
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  1. #1
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    Default Midi fighter mod question

    i want to add some line faders to a custom midi fighter project i am trying to make. I know you have to use 10k line faders but am having trouble finding them in aus. Anyone know of any good places to buy them that will get to australia cheap. Also i have a old djx 700 laying around i couldn't rob the faders off that could i.

    I am adding some buttons as well is there anything else i need to add to the digital inputs to get them to work or just a straight wire in. I thought i read somewhere i need to add some resister or something.

    Any help will be appreciated.

  2. #2
    Tech Wizard jasonmd2020's Avatar
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    I think FatLimey mentioned a "pull-up" resistor is needed for the digital inputs. But I have no clue how to wire the buttons in. Gotta 2-prong button and three terminals to wire to... Uh...I'm a bit clueless here...
    "The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs. There's also a negative side."
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  3. #3
    Tech Guru Fatlimey's Avatar
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    Pull-up resistors are really simple. The idea is to feed a positive voltage to the digital input through a resistor while the switch is open. When the switch closes the current is directed away from the digital input because it has an easier way to ground through the switch. This "pulls the input low" when the switch is closed.

    So an open switch reads as a "1" to the input pin and a closed one reads as a "0". The logic inside the Midifighter already handles this.

    Code:
     +------o +5v
     |
     #  10k resistor
     #
     |
     +------o DigitalIn
     |
       /  switch
      /
     |
     |   
     +------o Gnd
    I found out recently that the Midifighter chip has 10k resistors built into the chip that just need to be enabled, so I'll be making that change in the next firmware. Until then, best to add a pull-up resistor just make the switch inputs rock solid reliable.

    [edit]
    A quick note on what happens when you don't use a pull-up resistor. Pins on the chip can have three states - connected to +5v ("HIGH"), connected to ground ("LOW") and not connected to anything ("Not Connected" or "NC"). The Not Connected state is also known as "High Z" which is a super opaque way of saying that it's not electrically connected. Pins in HighZ mode are prone to picking up radio signals and producing essentially random inputs. Connecting a switch from the pin to +5v will toggle between HIGH and NC modes rather than HIGH and LOW and yes, it will seem to be working after a fashion, but you will have a lot of unpredictable strangeness that will cause you to think the switches are haunted. :-)

    Pull up resistors make the device predictable.
    Last edited by Fatlimey; 03-23-2010 at 12:13 PM.

  4. #4
    Tech Wizard jasonmd2020's Avatar
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    Sweet. Off to Radio Shack!
    "The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs. There's also a negative side."
    -Hunter S. Thompson

  5. #5
    Tech Wizard jasonmd2020's Avatar
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    Ok let me just get the wiring straight here:

    This is what I'm guessing based on the diagram. The +5v with the pull up resistor connected to the same pin on the button as the digital input, with the ground on the other pin. Will this work, or am I gonna blow my MF up?

    Still trying to wrap my head around the electronics notation. I think a copy of Electronics for Dummies is in order.
    "The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs. There's also a negative side."
    -Hunter S. Thompson

  6. #6
    Tech Guru Fatlimey's Avatar
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    That's right, you connect the +5v through a resistor to the pin. You then connect the pin, through a switch to the ground. Feel free to move wires and connections around so long as you keep the same topology, for example soldering the resistor to one of the legs of your switch and also connecting another wire from that same solder joint to the digital input.

    Consider soldering a female "header" to the Midifighter board so you're not soldering directly into the motherboard, then you can just push the stripped ends of your wires into the slots until you're ready to commit your design:



    If you're feeling nervous, try it out using a breadboard first. So long as you don't use any voltages higher than the onboard +5v you'll be fine. Those chips are pretty robust. I should know, I've been abusing them for a while now, like soldering things while it's still switched on and connected to the PC... naughty!

  7. #7
    Tech Wizard jasonmd2020's Avatar
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    Just breadboarded it. Works! Now to start drillin' holes in the lunchbox I got to house the MF & mount the extra controls....
    "The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs. There's also a negative side."
    -Hunter S. Thompson

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    thank you heaps fatlimey, I am off to jaycar now to grab some parts.

    On another note i am trying to find some good quality faders to add onto the board to run the effects amounts, any good websites you or anyone know about to order them. I would like 100mm but any will really do.

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    Quote Originally Posted by Brad_webb_87 View Post
    thank you heaps fatlimey, I am off to jaycar now to grab some parts.

    On another note i am trying to find some good quality faders to add onto the board to run the effects amounts, any good websites you or anyone know about to order them. I would like 100mm but any will really do.
    When searching use terms like 'linear slide potentiometer'

    I also recommend 60mm or 75mm MAX!, slide potentiomenters. 100mm are MASSIVE so doing quick stuff if a little bit harder. but its up to you!

    i got mine from http://au.farnell.com/ (they have cheap and expensive faders of all sizes, highly recommended for EVERYTHING, i am in northern NSW and i ordered one day and had my bits the next)

    but another good aussie site is http://www.futurlec.com.au/ (cheap, but bad customer service enquiries etc)

    and if you need anything else apart from faders etc www.littlebirdelectronics.com.au (these guys are great, i got a handwritten thankyou card, and they ship with a neat little ikea plastic turpperware contain to house your extra bits, i love these guys!)

    just give me a yell if you need anymore help.

  10. #10
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    thankyou Mickolx that farnell website is great i was half way through ordering and ran into some questions hopefully someone can help me out.

    The website is http://au.farnell.com/

    I was looking at 60mm line faders with a product code 8796173, they say they are 10k ohm with 20 +/- tolerance will these faders be adequate for the midi fighter and work properly.

    For the step up resistor it was said i need a 10k ohm resister i searched and found this one Product code 1179775 i think it should be alright but i dont have a great electrical knowledge.

    I am looking at buying a header for the board does anyone know the crimp spacing required.

    Northern NSW hey where abouts i grew up in Alstonville moved to Brisbane about 3 years ago.

    Thankyou everyone in advance.

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