Giant MIDI fader controller

[drumbliss]

I'm getting ready to build a single giant MIDI fader controller, about 2 feet in length, to use with my live setup.

As far as the mechanical design, I'm planning on building the fader mechanics and have them control a small rotary potentiometer via a belt system.
For the rotary MIDI controller, I used Brendan Ratliff's "Knobber" as inspiration.

Current questions:

1) Why did he need to use a small capacitor to smooth out data, and which capacitor should I get (he didn't specify)
2) I'm not going to need the button he added, can I still use the same code?

Thanks.

Max.

 

[PaulStoffregen]

Once thing to consider is the limited resolution of a 7 bit MIDI parameter. That gives you 128 possible positions, which is usually fine for relatively small controls. Maybe it's ok for this too? 2 feet divided by 128 works out to be 3/16th inch motion to change the MIDI parameter by 1 minimum step. Is 3/16th inch sensitivity ok?

That's if your belt drive perfectly maps the range of motion from the slider to the pot. A safe design would probably have hard mechanical stops on the slider so the belt can't apply torque to the pot that would force it very close to or beyond its range of motion. The pot has tiny mechanical stops internally which are suitable for the torque from a finger turning a small knob, but a giant slider with a belt drive can probably apply far more torque to that little pot. Still, the analog reading from the pot has much more resolution, so you could figure out what numerical range the pot actually measures and edit the code to map that range to the 0-127 values of the MIDI control.

As for your original question, his diagram looks like it says a 100 ohm pot and 0.1 uF capacitor. Those values look pretty reasonable. A 1K pot would probably work quite well too, and 1K is a much more commonly available value.

That code looks like it ought to work as-is without the pushbutton connected, because it uses INPUT_PULLUP mode.

 

[MuShoo]

Once thing to consider is the limited resolution of a 7 bit MIDI parameter. That gives you 128 possible positions, which is usually fine for relatively small controls. Maybe it's ok for this too? 2 feet divided by 128 works out to be 3/16th inch motion to change the MIDI parameter by 1 minimum step. Is 3/16th inch sensitivity ok?

There is, in fact, a way to use MIDI at 14-bit resolution (which is higher than the ADCs on a Teensy 2 -- not sure about Teensy 3). The MIDI spec provides for splitting the MSB and LSB of a 14-bit number into two 7-bit Continuous Controller (CC) #'s - the MSB goes on CC_X and the LSB goes on CC_X+32. For instance, the Mod Wheel parameter on just about every midi controller has it's MSB on CC 1, and the LSB on CC 33. Some synthesizers (not all of them, I'd suggest you code this with a toggle if you're using MIDI learn) will automatically recognize if you're using a 14-bit CC setup. The MIDI Spec allows for CC's 0-32 to have their matched LSB on CC's 33-64. (ref: http://www.srm.com/qtma/davidsmidispec.html )

If you for some reason need more than 32 14-bit CC's, research NRPN's - this is a good brief overview of them: http://en.wikipedia.org/wiki/NRPN Note that NRPN stands for 'Non-registered Parameter Number' so there's no standardized setup for them, you'll have to either match your synth's/DAW's use of them, or only be interpreting those controllers yourself, via MaxMSP or some other custom-coded software.