Expanding original MIDI Fighter

DJTT Gear & Custom Mods Midi Fighters
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1

Expanding original MIDI Fighter

Recently got my hands on an original MIDI Fighter DIY board (#361/500 if you’re interested). I’m going to build this into a case, and I want to take advantage of the ability to add some digital and analog controls. I’m planning to add 4 buttons (dig), 2 pots, and 2 faders (ana).

I know very little about electrical stuff, so here are my questions:

When considering the pots, should I be looking for a specific resistance/power combo, or range?

For example, is there an advantage to using a 10 kOhm/0.125 W slider vs. a 100 kOhm/22 mW? Or is a 2.5kOhm/1 W rotary going to somehow underperform a 25 kOhm/1 W?

Additionally, what’s the difference between a single and dual gang slider?

Lastly, since I’m not going with the standard layout (I’m going to use 30mm buttons to give me a little more room), do you have any suggestions on what to do with the activity LEDs? I know that they play an important feedback role when working with the firmware. The LEDs are pretty small and really down in there on the board, so I think that de-soldering them so I can physically relocate them is pretty much out of the picture, so what’s my best bet? The worst-case-scenario option is that I mount the board in the project box, and use enough wire between my control surface and the board so I can physically remove the top while maintaining the connections, and I just have to open the project box when I need to interact with the firmware. But I’m hoping you have a better idea so I can keep the thing closed and still enjoy the pretty lights.

I’m absolutely certain that I sound like a complete idiot here, and I really appreciate your feedback.

2

So, I spoke with some folks at my local electronics shop, and they advised me that the power rating on the pots will not have much effect in this application. However, the resistance factor will. I looked at some projects from other folks, and I found that they used 10k Ohm pots. The guys at the shop advised that if I’ve seen other folks be successful with a particular resistance, then I should just stick with that, so 10k Ohms it is.

and it’s seeming like the computer-based MIDI Fighter manager does all the functions that the on-board firmware manager does, so I think that losing sight of the LEDs is not going to be a deal-breaker.

I’ll post more as my build moves forward.

3

10k Ohm pots are indeed the one’s that i would recommend, I would advise you to reconsider swapping out the 24-mm buttons for the larger ones since they are expensive and the LED’s really are nice to have. Furthermore adding these extra buttons is super easy and just a case of soldering them on the PCB.

Edit: In this case you might even be better off selling the MF PCB and using a Teensyduino as brain.

4

Okay, one more ultra stupid question -when using the D1 - D4 expansions for buttons, do I connect the other side of the button to the 5v power, or to the Ground? Thanks, folks!

5

Ground, but again, i really recommend picking another brain.

Edit: No pull-up resistors are required nor do the need to debounce the inputs

Edit 2:
Here’s how to enable these inputs:

Entering and Using Menu Mode

To enter Menu Mode, hold down the top-left key while resetting the
Midifighter. You can power on the Midifigher by either by plugging in the
USB cable, or by pressing an optional 6mm tactile “reset” switch that can be
soldered to the top left of the motherboard.

Once in Menu Mode, the LED will display 7 option keys and a flashing “exit”
key:

        • ← Menu items
      • .
        . . . .
        . . . # ← Flashing exit key

To leave any Menu page or the Menu system itself, just hit the flashing Exit key.

Any changes made to the options are only written to the Midifighter if you
exit the Menu Mode through the top level “exit” key - this allows you to
play with the options and be sure your settings are correct before
committing the changes, without having to remember previous values.
Only when you are sure the Midifighter is set up to your specifications
should you use the top level “exit” button to commit your changes.

The seven menu items are:

  1. MIDI channel

  2. MIDI velocity

  3. empty

  4. Enable Keypress LED

  5. Select Fourbanks mode

  6. Select Expansion port Digital inputs

  7. Select Expansion Port Analog inputs

  8. Select Expansion Port Digital Inputs

. . . .
. # . . ← Flashing exit key

        • ← one LED for each digital input, click to toggle
          . . . .

Enabling this option causes the Midifighter to read the values of the
external digital input pins and track their state using a debounce
buffer. Each LED can be individually toggled to enable MIDI events to be
read from that digital input.

NOTE: If Fourbanks External mode has been selected, this menu page is
disabled as the digital inputs are being used as Bank Select keys.

  1. Enable Expansion Port Analog Inputs

. . . .
. . # . ← Flashing exit key

        • ← one LED for each Analog input, click to toggle
          . . . .

Enabling this option causes the Midifighter to read the analog values of the
external Analog Inputs and generate MIDI events. Each analog input channel
acts as a “Smart Fader”, outputting two CC values and two KeyDown events
along the range.

6

replacing roasted sliders

Had I known this great sale was coming up, I might have saved myself a lot of hassle and expense. And I totally respect DJDoubleYou’s advice on the brain - I’m seeing how building ground-up can have some significant advantages. But I’m dedicated to making this project work now, so I have another question:

I finally got everything hooked up last night and gave it a test run. I had some erratic performance issues with the additional digital and analog inputs. I didn’t solder my points to the MIDI Fighter board (my hands just aren’t steady enough for that kind of precision work), but I found a set of Molex headers that fit the pin holes perfectly, so I soldered my leads to that and connected from there. The headers fit firmly in the holes, so I think I’m getting good connection, but I was receiving erratic performance from the 2 faders on the analog inputs, and consistently had 1 of the digital buttons unresponsive.

Then, I got that smell that everyone who has ever worked with electronics knows and fears. I think something must have touched inside the box, and I roasted one of my slider pots.

The post I used initially were Bourns PTB6043-2010BPB103 (ref: http://www.digikey.com/product-search/en?keywords=PTB6043-2010BPB103-ND ) - 10k Ohm, .25W, 60mm

I’m wondering if the erratic response I was getting was due to these being the wrong faders for the job. Does anyone have a recommendation of a different fader, or do you think these ones are OK? I’m going to have to order at least one more to replace Mr. Char-broil, so if I should replace both, this is an opportune time.

Thanks, folks!

7

I think you messed up something in the wiring because the values of those faders are fine.

8

OK, I replaced the failed fader, and after using my multimeter, I found that I had misidentified which post was the power and which was the wipe, so at least that’s all cleared up.

So I wired everything back up, plugged it into my Mac, and I got a message that said that OS X shut down the USB ports because the USB item was pulling too much power. So, I pulled the pin on the 5v line (I’ve got header leads in a little Molex block to help me), thus disabling the analog controls. All of the 16 typical buttons then worked just fine, but only 3 of the digital buttons worked (D1, D2, and D4). If I pull the analog headers, then D3 works.

For the life of me, I can’t figure out what’s going on. I’m reasonably certain that I’ve for everything wired properly, so now I’m starting to wonder if there’s something wrong with the board itself.

Now, the analog controls aren’t a total necessity, but I’d really like to be able to make them work - I’m open to any ideas that anyone may have.

9

What happens when you short the fader and +5v and GND sequentially? Does the controller output 0-127 midi messages?

10

I can’t get past the “too much juice to the USB port” error to even be able to check if the faders and/or pots are actually transmitting signal. I’ve tried isolating the analog inputs to see if there’s one in particular that’s the issue, but it’s all the same.

But then a thought came to me today. I’m not sure if DJDoubleYou will know this one (I suspect he’s the only one reading my rant here - and I’m very thankful for that, though I feel like I’m leaning on the guy too heavily!) – when connecting the analog controls, should I have a capacitor or a resistor in-line? I’ve seen that with some brains there is a need to do this, but with others there is circuitry in the board that makes it so the extra item isn’t needed. Could the lack of a capacitor or resistor be what’s at the core of my issues? If so, how do I figure out what I need? Thanks!

11

I do not think that is is due to the lack of a resistor or capacitor, if i remember correctly it really should just be the case of connecting the inputs to the extension pots, have you checked if the MF still works without them?

12

The MIDI Fighter definitely works without the analog items connected – all 16 of the regular buttons (and the LED light show) work perfectly, and the 4 digital buttons work perfectly so long as I have the 5v and all 4 analog inputs pulled.

I’m thinking I’m just going to give up on trying to make the analog inputs work on this. Being able to do the bank select with the 4 digital buttons and having the 16 main buttons working is really great functionality for me.

13

Sorry man, I have a pro and a spectra, if I had a classic I could have been of more assistance, unfortunately I have absolutely zero experience with this controller.

14

The Pro is basically an expanded Classic :wink:

15

I know but opening it up is a pain since the upper right button’s (top view) right pin is soldered to the PCB (unfortunate design fault).