Reads keypress information and translates to midi notes. See comments for details.

keyboard.rb

# This reads from key presses from a serial device (such 
# as an arduino) in the following form:
# +4-2+11
# this means that the keys 4 and 11 are engaged 
# and key 2 is not engaged. Use the keys map below 
# to map keys to midi notes

require 'unimidi'
require 'serialport'

keys = { 
  '2' => 60,
	'3' => 62,
	'5' => 64,
	'6' => 65,
	'8' => 67,
	'9' => 69,
	'11' => 71,
	'12' => 72
}

pressed = Hash.new false
midi = UniMIDI::Output.first

arduino = SerialPort.new '/dev/tty.usbmodem1411'
arduino.baud = 9600
arduino.data_bits = 8
arduino.stop_bits = 1

loop do 
	arduino.readline.split.each do |info|
		state, key = info[0], info[1..-1]
		next unless keys.include? key

		if state == '+' and not pressed[key]
			midi.puts(0x90, keys[key], 100)
			pressed[key] = true
		end

		if state == '-' and pressed[key]
			midi.puts(0x80, keys[key], 100)
			pressed[key] = false
		end
	end
end