tl_velocity_blinker.ino

int incomingByte = 0;
int firstLedPinNum = 10;
int lastLedPinNum = 13;
int ledBlinkFactorSec = 100

void setup() {
  Serial.begin(9600);

  for(int i = firstLedPinNum; i <= lastLedPinNum; i++) {
    pinMode(i, OUTPUT);
  }
}

void loop() {
  if (Serial.available() > 0) {
    incomingByte = Serial.read();

    int ledBlinkTime = incomingByte * ledBlinkFactorSec;

    while(Serial.available() == 0) {
      for(int i=firstLedPinNum; i <= lastLedPinNum; i++) {
        digitalWrite(i, HIGH);
        delay(ledBlinkTime);
        digitalWrite(i, LOW);
      }
    }
  }
}

tl_velocity_sender.rb

require 'serialport'
require File.expand_path(File.dirname(__FILE__)) + "/tweet_counter"

class TLVelocitySender
  def initialize(serial_port_path)
    @serial_port_path = serial_port_path
    @measure = TweetCounter.new
    @max_velocity = 10
  end

  def periodically_send(period_sec)
    sp = SerialPort.new(@serial_port_path, 9600)

    @measure.start_periodic_count(period_sec) do |count|
      velocity = count > @max_velocity ? @max_velocity : count
      led_blink_time = (@max_velocity - velocity) + 1
      sp.print led_blink_time.chr
    end
  end
end

if __FILE__ == $0
  sender = TLVelocitySender.new("/dev/tty.usbmodem1431")
  sender.periodically_send(30)
end

tweet_counter.rb

require "tweetstream"

class TweetCounter
  def initialize
    TweetStream.configure do |config|
      config.consumer_key       = '__CONSUMER_KEY__'
      config.consumer_secret    = '__CONSUMER_SECRET__'
      config.oauth_token        = '__OAUTH_TOKEN__'
      config.oauth_token_secret = '__OAUTH_TOKEN_SECRET__'
      config.auth_method        = :oauth
    end

    @tweet_counter = 0
  end

  def start_periodic_count(period_sec)
    Thread.new do
      loop do
        sleep(period_sec)
        yield @tweet_counter
        @tweet_counter = 0
      end
    end

    TweetStream::Client.new.userstream do |status|
      warn status.text
      @tweet_counter += 1
    end
  end
end

if __FILE__ == $0
  measure = TweetCounter.new
  measure.start_periodic_count(10) {|velocity| puts velocity }
end