I have created a wrapper library to make programming MIDI controllers on the Teensy board dead easy and super fast. Simply instantiate object for each component like Buttons, Potentiometer, LED, rotary encoders, etc. and let the library handle all the dirty work of reading the raw values and deciding when to send MIDI signals. Enabling you to experiment and concentrate on your creative ideas and not waste too much time with the repetitive technical details and debugging code.

Just in a couple lines of code you can program a fully functioning MIDI controller.
Here’s an example of how simple things are:

boolean debug=false; // print to serial instead of midi
boolean secondary=true; // enable secondary midi messages
int midiChannel=1; // midi channel number

// declare all your components here
Button but(17,midiChannel,1,secondary,debug); // button 1 on pin 17
Button but2(16,midiChannel,2,secondary,debug); // button 2 on pin 16
Potentiometer pot(45,midiChannel,3,secondary,debug); // knob on pin 45 (A7)
Led led(15,midiChannel,3,true); // led on pin 15 with PWM enabled, triggered on the same number as pot

void setup(){
  usbMIDI.setHandleControlChange(OnControlChange); // set event handler for CC
}

void loop(){
  // add here all the input component reads
  pot.read(); // read knob and send midi messages
  but.read(); // read buttons and send midi messages
  but2.read();
  usbMIDI.read(); // read all the incoming midi messages
}
//====================================================================
// event handlers
void OnControlChange(byte channel, byte control, byte value){
  // add all your output component sets that will trigger with cc
  led.setOn(channel,control,value);
}

Currently only Buttons, Potentiometers and LEDs are supported. But I’m planning on adding RGB LED, rotary encoder, LED bars and ring and button pad classes.
Each component sends two sets of MIDI signals if enabled. For example Buttons send NoteOn, NoteOff, as well as ControlChange values so that they could be easily mapped in Toggle or Instant mode in software like Ableton Live. Also the Potentiometers send secondary NoteOns when values reach 0 or 127, à la MIDI Fighter Pro.

Download: github
To install extract the MIDIElements folder in your arduino/libraries directory

Here are the methods for each class:

Button:
Constructors

Button(byte pin);
Creates a button object with default channel 0, MIDI number 0 and debugging enabled
pin – pin number on Teensy

Button(byte pin, byte channel, byte number);
Creates a button object on specified channel and MIDI number
pin – pin number on Teensy
channel – midi channel on which messages will be sent
number – midi value on which messages will be sent

Button(byte pin, byte channel, byte number, bool secondary);
Creates a button object on specified channel and MIDI number
pin – pin number on Teensy
channel – midi channel on which messages will be sent
number – midi value on which messages will be sent
secondary – send secondary midi signals

Button(byte pin, byte channel, byte number, bool secondary, bool debugging);
Creates a button object on specified channel and MIDI number
pin – pin number on Teensy
channel – midi channel on which messages will be sent
number – midi value on which messages will be sent
secondary – send secondary midi signals
debugging – print messages to serial port instead of midi

Functions
read();
Reads the button state and sends a midi note on if the button was pressed and note off if the button was unpressed on the channel and midi number specified in the constructor

readValue(bool &stateChanged);
Reads the button state, and sets the stateChanged if the state changed from the last time checked, also returns true if the button is pressed and false if not pressed. No MIDI signals are sent.
stateChanged – is set to true after the function exits if the button state changed state

setVelocity(byte velocity);
Changes the velocity value for note on messages, default velocity is 127.
velocity – note on velocity

Potentiometer:
Constructors

Potentiometer(byte pin);
Creates a potentiometer object with default channel 0, MIDI number 0 and debugging enabled
pin – pin number on Teensy

Potentiometer(byte pin, byte channel, byte number);
Creates a potentiometer object on specified channel and MIDI CC number
pin – pin number on Teensy
channel – midi channel on which messages will be sent
number – midi value on which messages will be sent

Potentiometer(byte pin, byte channel, byte number, bool secondary);
Creates a potentiometer object on specified channel and MIDI number
pin – pin number on Teensy
channel – midi channel on which messages will be sent
number – midi value on which messages will be sent
secondary – send secondary midi signals

Potentiometer(byte pin, byte channel, byte number, bool secondary, bool debugging);
Creates a potentiometer object on specified channel and MIDI number
pin – pin number on Teensy
channel – midi channel on which messages will be sent
number – midi value on which messages will be sent
secondary – send secondary midi signals
debugging – print messages to serial port instead of midi

Functions
read();
Reads the potentiometer value and sends a control changed if the value changed on the channel and midi number specified in the constructor

readValue(bool &stateChanged);
Reads the potentiometer value, and sets the stateChanged if the state changed from the last time checked, also returns the value of the potentiometer. No MIDI signals are sent.
stateChanged – is set to true after the function exits if the button state changed state

Led:
Constructors

Led(byte pin);
Creates a Led object with default channel 0, MIDI number 0 and debugging enabled
pin – pin number on Teensy

Led(byte pin, byte channel, byte number);
Creates a Led object on specified channel and MIDI CC number
pin – pin number on Teensy
channel – midi channel on which led will be triggered
number – midi value on which led will be triggered

Ledr(byte pin, byte channel, byte number, bool pwm);
Creates a Led object on specified channel and MIDI number
pin – pin number on Teensy
channel – midi channel on which led will be triggered
number – midi value on which led will be triggered
pwm – enable pulse width modulation

Functions
setOn(byte channel, byte number, byte velocity);
Call from within Note On or Control Change event handler and pass on the parameters. And the LED will turn on if the messages received correspond to those specified in the constructor.
channel – midi channel of the received message
number – midi number or control change of the received message
velocity – midi velocity or control change value of the received message

setOff(byte channel, byte number, byte velocity);
Call from within Note Off event handler and pass on the parameters. And the LED will turn off if the messages received correspond to those specified in the constructor.
channel – midi channel of the received message
number – midi number or control change of the received message
velocity – midi velocity or control change value of the received message