How to Blink an LED on Raspberry Pi 3 Model B+

In this post, I’ll show you how to blink an LED on Raspberry Pi 3 Model B+. This project shows you how to use the Raspberry Pi’s GPIO (General Purpose Input Output) pins as an output to manipulate an external device (in this case the LED).

Requirements

Here are the requirements:

  • Make an LED blink on Raspberry Pi 3 Model B+.

You Will Need

The following components are used in this project. You will need:

Directions

Set up the Raspberry Pi

Set up the Raspberry Pi as explained in this video:

Explore the Raspberry Pi (Optional)

From the Raspberry Pi desktop, click the Pi logo, and go to Preferences -> Raspberry Pi Configuration. Make sure your settings look like the image below and reboot (we’ll make use of these settings in future posts):

blink-led-11

Before we dive into the LED project, let’s have a look at the Raspberry Pi terminal.

The terminal is a way to communicate with your computer. Back in the 1980s and early 1990s when I first started using computers, the command-line interface of the terminal was the main way to send commands to your computer.

Back in those days computers did not have the processing power they have now. If you were born in the 1990s or later, you probably have only interacted with your computer via a graphical user interface. I like to use the command-line interface for robotics projects because it is more efficient, and you can tell the computer exactly what to do.

To open the terminal, click the Raspberry Pi logo in the upper left of the Raspberry Pi desktop and go to Accessories -> Terminal.

That black window you are looking at is the terminal. Typing ls will display all the files and folder in that directory. Blue items are directories. Green text shows our username (i.e “pi”).

blink-led-12

To change to a directory, you use the cd Directory Name command. For example cd Documents, gets you to the Documents directory.

Determine What Resistor to Use

Find out what the forward voltage is of your 5mm LED. Forward voltage is the minimum voltage required in order for the LED to light up. The forward voltage for my red LED is 1.8-2.2V.

Raspberry Pi is powered by 5V micro USB (2.5A). Each GPIO (General Purpose Input Output) pin supplies 3.3V (our source voltage) and can provide 16mA of current. Since 3.3V > 2.2V, we know that Raspberry Pi has enough voltage to power the LED.

Forward voltage is also the amount of voltage lost when a current runs through the LED. Consider it the “voltage drop” across the LED. To understand the basics of this concept, check out this 3D animation.

Find out what the maximum forward current of the 5mm LED is. Maximum forward current is the maximum current the LED can handle before it is at risk of getting damaged. The maximum forward current of my LED is 20mA (0.02A), which I obtained from the LED’s datasheet.

Now, we calculate the value of the resistor we need using Ohm’s Law (V = I * R):

  • Source voltage in volts = 3.3V
  • Forward voltage of LED = 1.8V
  • Maximum current of LED = 20mA = 0.02A
Resistor in ohms = ((Source voltage in volts) - (Forward voltage of LED in volts)) / (Maximum current in amps) = (Voltage leftover after the LED drops some of it) / (Maximum current)
Resistor in ohms = (3.3 - 1.8) / 0.02 = 75 ohms

So, we need at least a 75 ohm resistor. I’ll chose 330 ohms. The higher the resistor value you use, the dimmer the LED.

What is the current (represented as the capital letter ‘I’) in this case?

(3.3V - 1.8V) = I * 330
I = 4.5mA (which is well under the 20mA max current)

Now, we need to calculate how much power the resistor the LED can dissipate before it fails. We use this equation (P = VI):

Power in watts = Voltage in volts * Current in amps
Power in watts = (3.3 - 1.8) * 0.02A = 0.03 watts

Our resistor is rated at 0.25 watts, so we have more than enough cushion. We are good to go!

Wire the LED to the Breadboard

Here is the diagram to use to wire (using male to female jumper wire) the 330 ohm resistor and 5mm LED to the Raspberry Pi. That kink in one of the LEDs represents the long leg of the LED:

blink_led
blink-led-2

Blink the LED

Now we need to write a program in Python to blink the LED.

I have a folder in my Home Directory named robot. I get to this directory by opening up a terminal window in Raspberry Pi and typing:

cd robot

Now, we open up the Nano text editor to enable us to write the Python program. We name it led_blink.py. Here is the terminal command:

nano led_blink.py

We type in this python code:

import gpiozero  # The GPIO library for Raspberry Pi
import time  # Enables Python to manage timing

led = gpiozero.LED(17) # Reference GPIO17

while True:
  led.on() # Turn the LED on
  time.sleep(1)
  led.off() # Turn the LED off
  time.sleep(1)  # Pause for 1 second

We then press CTRL-X, then Y, then press Enter to save the program and return to the terminal.

To run the program, we type:

python3 led_blink.py

Your LED should be blinking. If it doesn’t blink, try connecting the red positive lead to another GPIO pin on the Raspberry Pi.

blink-led-3
blink-led-4

To stop the program, you press CTRL-C.

You can also try different color LEDs, as shown below.

blink-led-5
blink-led-6
blink-led-7
blink-led-8
blink-led-9
blink-led-10

UART vs I2C vs SPI – Communication Interfaces for Raspberry Pi

The Raspberry Pi provides us with three main communication protocols. These protocols enable devices such as sensors, display modules, other computers, and scientific instruments to communicate and exchange data with the Raspberry Pi.

Here are the communication protocols in order from slowest to fastest:

  • UART = Universal Asynchronous Receiver / Transmitter
  • I2C = Inter-Integrated Circuit
  • SPI = Serial Peripheral Interface

These methods are digital, serial communication protocols.

UART vs I2C vs. SPI Comparison

Speed

UART is slow. I2C is faster but not as fast as the SPI. SPI has a data transfer rate that is roughly twice as fast.

Number of Devices

I2C is the easiest of the three protocols for chaining multiple devices. I2C supports multiple masters and slaves. It enables up to 127 devices without extreme complexity. On the other hand, SPI gets hairy beyond two devices because a select signal line is required for each device. UART only can handle two devices.

Transmission Confirmation

I2C is the only communications protocol that ensures the data that was sent to the slave device was actually received.

Number of Wires

I2C only uses two wires. UART uses two wires, but it is slow. SPI needs four wires.

Popularity

I2C is well known and widely used. I2C has a formal standard while SPI does not.

Price

I2C is cheaper to implement than the SPI communication protocol.

Noise

I2C has less noise than SPI.

Distance

I2C can send data over greater distances than SPI. SPI is really limited to short distance communication.

How to Send Roll, Pitch, & Yaw Data Over I2C From Arduino to Raspberry Pi

In this post, I’ll show you how to send roll, pitch, and yaw data over I2C using Raspberry Pi and Arduino. We’ll also capture GPS data on the Raspberry Pi to make things interesting for when I mount everything on a quadcopter.

Requirements

Here are the requirements:

  • Using the IMU connected to the Arduino, capture roll, pitch, and yaw data.
  • Using the GPS connected to the Raspberry Pi, capture latitude, longitude, and altitude data.
  • Send the IMU data via I2C to the Raspberry Pi.
  • Send the IMU and GPS data via Bluetooth from Raspberry Pi to my host computer (e.g. my personal laptop).
  • Display the data on my host computer.
  • To make things interesting, I mounted all the equipment on a quadcopter.

Design

Hardware

The following components are used in this project. You will need:

Software

Here are the steps for the GPS Poller, responsible for capturing Latitude+Longitude+Altitude data on the Raspberry Pi:

  • Open a new file to log the GPS data
  • Create a GPS Poller class
  • Log the latitude data
  • Log the longitude data
  • Log the altitude in feet
  • Delay 5 seconds
  • Close file

Here are the steps for the IMU I2C program on the Arduino, responsible for capturing Roll+Pitch+Yaw data and sending to the Raspberry Pi:

  • Set the delay between fresh samples
  • Define a flag to stop the program
  • Make the Arduino a slave to the Raspberry Pi by defining a slave address
  • Declare a byte array of size 12, which will be the roll+pitch+yaw data (with the sign) to send back to Raspberry Pi
  • Declare variables used for digit extraction
  • Declare function to end the program
  • Display some basic information on the IMU sensor
  • Display some basic info about the sensor status
  • Display sensor calibration status
  • Create method that sends a byte array (of size 12) when reading request is received from the Raspberry Pi
  • Create method that retrieves the digit of any position in an integer. The rightmost digit has position 0. The second rightmost digit has position 1, etc. e.g. Position 3 of integer 245984 is 5.
  • Create Arduino setup function (automatically called at startup) — 9600 Baud Rate
  • Initialize the sensor
  • Set up the Wire library and make Arduino the slave
  • Define the callbacks for i2c communication
  • Need callback that specifies a function when data is received from the RPi Master
  • Need callback that specifies a function when the Master requests data from the Arduino
  • Arduino loop function, called once ‘setup’ is complete
  • While not done:
    • Get a new sensor event
    • Display the floating point data and capture the roll, pitch, and yaw data. Cast the floats to signed integers.
    • Store each digit of the roll, pitch, and yaw data into a byte array (which will be sent to the RPi)
    • End program
  • While true infinite loop

Here are the steps for the I2C Python program on the Raspberry Pi, responsible for sending messages and requesting IMU data via I2C from the Arduino slave:

  • Open a new text file to log the IMU data
  • Set up slave address in the Arduino Program
  • Read a block of 12 bytes starting at SLAVE_ADDRESS, offset 0
  • Extract the IMU reading data
  • Print the IMU data to the console
  • Write the IMU data to the text file
  • Close text file when done
  • Request IMU data every 5 seconds from the Arduino

Implementation

The most straightforward way to connect the Arduino board to the Raspberry Pi is using the USB cable, as I have done in previous projects. However, we can also use I2C. I2C uses two lines: SDA (data) and SCL (clock). It also uses GND (ground).

Here are the connections that I made between the Raspberry Pi and the Arduino:

  • Raspberry Pi SDA (I2C1 SDA) –> Arduino SDA
  • Raspberry Pi SCL (I2C1 SCL) –> Arduino SCL
  • Raspberry Pi GND –> Arduino GND
imu_i2c_1

Raspberry Pi 3 Pin Mappings. Image Source: Microsoft.com

imu_i2c_2

Arduino Uno Pin Mappings. Image Source: Electronics Schematics

Here is the schematic I followed.

imu_i2c_3

Image Source: Monk (2016)

The BNO055 (IMU) was wired to the Arduino Uno using the solderless breadboard as follows:

  • Connected Vin to the power supply of 5V
  • Connected GND to common power/data ground
  • Connected the SDA pin to the I2C data SDA pin on the Arduino (A4).
  • Connected the SCL pin to the I2C clock SCL pin on the Arduino (A5).

To get started with the implementation, I tested the GPS device to see if I can successfully capture GPS latitude + longitude + altitude data on the Raspberry Pi and save it to a text file. This data will later get sent via Bluetooth from Raspberry Pi to my Host computer (HP Omen laptop with Windows 10).

GPS was connected to the Raspberry Pi via the USB cord. The commands for this are as follows:

To start the GPS stream, I typed:

sudo gpsd /dev/ttyAMA0 -F /var/run/gpsd.sock

To display the GPS data, I typed the following command:

cgps -s

Here is what the display looked like:

imu_i2c_4

Other commands I could have run are gpsmon and xgps.

gpsmon looks like this:

imu_i2c_5

xgps looks like this:

imu_i2c_6

Sometimes the GPS data did not show up immediately. When that occurred, I rebooted the Raspberry Pi by typing the following command:

sudo reboot

I typed the following command to shutdown the GPS stream:

sudo killall gpsd

Now, I want to do the same thing, but this time I want to save the GPS data to a text file. I will use this syntax in the command terminal in order to save the standard output stream to a text file.

command | tee output.txt

More specifically, I will type:

cgps -s | tee /home/pi/Documents/GPS/output.txt

The output.txt was created, and the data was logged in the file. However, it is more useful to output the GPS data in a more user-friendly format. To do this, I will run a Python script that is a GPS polling program. The code for this program is located in the Software section later in this report.

To create the program, I opened the Python IDE (Raspberry Pi -> Programming -> Python 3 (IDLE)).

I clicked File -> New File. I then added the code and saved the file as GPSPoller.py.

imu_i2c_7

To run the script, I typed

python GPSPoller.py

To stop the script, I pressed Ctrl-C. I could have also pressed Ctrl-Pause/Break.

imu_i2c_8

Here is the output of the locations.csv file. For the actual code when I flew the quadcopter, this file was named gps_data.txt.

imu_i2c_9

Here is how gps_data.txt looks:

gps_data

Next I connected Arduino to Raspberry Pi via I2C as pictured earlier in this section. I also connected them via USB in order to provide the Arduino with power and to easily upload sketches to the Arduino. BNO055 connects to Arduino.

Next, I followed the instructions inMonk (2016) to make the Arduino the Slave, and the Raspberry Pi the Master. I needed to write code for both the Arduino and the Raspberry Pi in order for them to communicate with each other via I2C (The code for Arduino and Raspberry Pi are in the Software section later in this report).

After writing the Arduino code for I2C communication and IMU data capture, I uploaded the code to the board. I then needed to enable I2C on the Raspberry Pi. I configured Raspberry Pi accordingly by going to Preferences under the main menu, and then clicking Raspberry Pi Configuration -> Interfaces -> Enable I2C.

I now installed the Python I2C library by using the command:

sudo apt-get install python-smbus

It was already installed. I then clicked:

sudo reboot

I had my Arduino Uno attached to the Raspberry Pi via I2C. I wanted to check that it’s attached and find its I2C address.

From a Terminal window on my Raspberry Pi, I typed the following commands to fetch and install the i2c-tools:

sudo apt-get install i2c-tools

It was already installed.

Next, I ran the following command:

$ sudo i2cdetect -y 1
imu_i2c_10

Next, I needed to write the code in Python that the Raspberry Pi can use to make requests for IMU data from the Arduino. That code, as I mentioned above, is in the Software section of this post. I will run this Python script in the terminal window and redirect the IMU data response from the Arduino slave to a text file.

The command to run the Python program is as follows:

sudo python ardu_pi_i2c_imu.py

A file named imu_data.txt will capture the Roll+Pitch+Yaw data. Here is how the data looks:

imu_data

Hardware

imu_i2c_hw 2
imu_i2c_hw 3

Software

Here is the Python script that logs the GPS latitude + longitude + altitude data into a text file on the Raspberry Pi:

from gps import *
import time
import threading

# Source: Donat, Wolfram. "Make a Raspberry Pi-controlled Robot :
# Building a Rover with Python, Linux, Motors, and Sensors.
# Sebastopol, CA: Maker Media, 2014. Print.
# Modified by Addison Sears-Collins
# Date April 17, 2019

# Open a new file to log the GPS data
f = open("gps_data.txt", "w")

gpsd = None

# Create a GPS Poller class. 
class GpsPoller(threading.Thread):
  def __init__(self):
    threading.Thread.__init__(self)
    global gpsd
    gpsd = gps(mode=WATCH_ENABLE)
    self.current_value = None
    self.running = True

  def run(self):
    global gpsd
    while gpsp.running:
      gpsd.next()

if __name__ == '__main__':
  gpsp = GpsPoller()
  try:
    gpsp.start()
    while True:
      f.write("Lat: " + str(gpsd.fix.latitude) # Log the latitude data
      + "\tLon: " + str(gpsd.fix.longitude) # Log the longitude data
      + "\tAlt: " + str(gpsd.fix.altitude / .3048) # Log the altitude in feet
      + "\n")
      time.sleep(5)
  except(KeyboardInterrupt, SystemExit):
    f.close()
    gpsp.running = False
    gpsp.join()

Here is the code for the IMU I2C program on the Arduino, responsible for capturing Roll+Pitch+Yaw data and sending to the Raspberry Pi:

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BNO055.h>
#include <utility/imumaths.h>

/* This driver uses the Adafruit unified sensor library (Adafruit_Sensor),
   which provides a common 'type' for sensor data and some helper functions.

   To use this driver you will also need to download the Adafruit_Sensor
   library and include it in your libraries folder.

   You should also assign a unique ID to this sensor for use with
   the Adafruit Sensor API so that you can identify this particular
   sensor in any data logs, etc.  To assign a unique ID, simply
   provide an appropriate value in the constructor below (12345
   is used by default in this example).

   Connections
   ===========
   Connect SCL to analog 5
   Connect SDA to analog 4
   Connect VDD to 3-5V DC
   Connect GROUND to common ground

   History
   =======
   2015/MAR/03  - First release (KTOWN)
   2015/AUG/27  - Added calibration and system status helpers

   @Author Modified by Addison Sears-Collins
   @Date   April 17, 2019
*/

/* Set the delay between fresh samples */
#define BNO055_SAMPLERATE_DELAY_MS (100)

Adafruit_BNO055 bno = Adafruit_BNO055(55);

// Flag used to stop the program
bool done = false;

// Make the Arduino a slave to the Raspberry Pi
int SLAVE_ADDRESS = 0X04;

// Toggle in-built LED for verifying program is working
int ledPin = 13;

// Data to send back to Raspberry Pi
byte imu_data[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};

// Variables used for digit extraction
int roll = 0;
int pitch = 0;
int yaw = 0;

// Initialize the LED. This is used for testing.
boolean ledOn = false;

/**************************************************************************/
/*
    This function ends the program
*/
/**************************************************************************/

void end_program() {
    
    // Used for reading data from the serial monitor
    char ch;

    // Check to see if ! is available to be read
    if (Serial.available()) {

    // Read the character
    ch = Serial.read();

    // End the program if exclamation point is entered in the serial monitor
    if (ch == '!') {
      done = true;
      Serial.println("Finished recording Roll+Pitch+Yaw data. Goodbye.");
    }
  } 
}

/**************************************************************************/
/*
    Displays some basic information on this sensor from the unified
    sensor API sensor_t type (see Adafruit_Sensor for more information)
*/
/**************************************************************************/
void displaySensorDetails(void)
{
  sensor_t sensor;
  bno.getSensor(&amp;sensor);
  Serial.println("------------------------------------");
  Serial.print  ("Sensor:       "); Serial.println(sensor.name);
  Serial.print  ("Driver Ver:   "); Serial.println(sensor.version);
  Serial.print  ("Unique ID:    "); Serial.println(sensor.sensor_id);
  Serial.print  ("Max Value:    "); Serial.print(sensor.max_value); Serial.println(" xxx");
  Serial.print  ("Min Value:    "); Serial.print(sensor.min_value); Serial.println(" xxx");
  Serial.print  ("Resolution:   "); Serial.print(sensor.resolution); Serial.println(" xxx");
  Serial.println("------------------------------------");
  Serial.println("");
  delay(500);
}

/**************************************************************************/
/*
    Display some basic info about the sensor status
*/
/**************************************************************************/
void displaySensorStatus(void)
{
  /* Get the system status values (mostly for debugging purposes) */
  uint8_t system_status, self_test_results, system_error;
  system_status = self_test_results = system_error = 0;
  bno.getSystemStatus(&amp;system_status, &amp;self_test_results, &amp;system_error);

  /* Display the results in the Serial Monitor */
  Serial.println("");
  Serial.print("System Status: 0x");
  Serial.println(system_status, HEX);
  Serial.print("Self Test:     0x");
  Serial.println(self_test_results, HEX);
  Serial.print("System Error:  0x");
  Serial.println(system_error, HEX);
  Serial.println("");
  delay(500);
}

/**************************************************************************/
/*
    Display sensor calibration status
*/
/**************************************************************************/
void displayCalStatus(void)
{
  /* Get the four calibration values (0..3) */
  /* Any sensor data reporting 0 should be ignored, */
  /* 3 means 'fully calibrated" */
  uint8_t system, gyro, accel, mag;
  system = gyro = accel = mag = 0;
  bno.getCalibration(&amp;system, &amp;gyro, &amp;accel, &amp;mag);

  /* The data should be ignored until the system calibration is > 0 */
  Serial.print("\t");
  if (!system)
  {
    Serial.print("! ");
  }

  /* Display the individual values */
  Serial.print("Sys:");
  Serial.print(system, DEC);
  Serial.print(" G:");
  Serial.print(gyro, DEC);
  Serial.print(" A:");
  Serial.print(accel, DEC);
  Serial.print(" M:");
  Serial.print(mag, DEC);
}

/**************************************************************************/
/*
    Callback for received data
*/
/**************************************************************************/

void processMessage(int n) {

  char ch = Wire.read();
  if (ch == 'l') {
    toggleLED();
  }
}

/**************************************************************************/
/*
    Method to toggle the LED. This is used for testing.
*/
/**************************************************************************/

void toggleLED() {
  ledOn = ! ledOn;
  digitalWrite(ledPin, ledOn);
  
}

/**************************************************************************/
/*
    Code that executes when request is received from Raspberry Pi
*/
/**************************************************************************/

void sendIMUReading() {
  Wire.write(imu_data, 12); 
}

/**************************************************************************/
/*
    Retrieves the digit of any position in an integer. The rightmost digit
    has position 0. The second rightmost digit has position 1, etc.
    e.g. Position 3 of integer 245984 is 5.
*/
/**************************************************************************/

byte getDigit(int num, int n) {
  int int_digit, temp1, temp2;
  byte byte_digit;

  temp1 = pow(10, n+1);
  int_digit = num % temp1;

  if (n > 0) {
    temp2 = pow(10, n);
    int_digit = int_digit / temp2;
  }

  byte_digit = (byte) int_digit;

  return byte_digit;
}

    
/**************************************************************************/
/*
    Arduino setup function (automatically called at startup)
*/
/**************************************************************************/
void setup(void)
{
  Serial.begin(9600);
  Serial.println("Orientation Sensor Test"); Serial.println("");

  /* Initialise the sensor */
  if(!bno.begin())
  {
    /* There was a problem detecting the BNO055 ... check your connections */
    Serial.print("Ooops, no BNO055 detected ... Check your wiring or I2C ADDR!");
    while(1);
  }

  delay(1000);

  /* Display some basic information on this sensor */
  displaySensorDetails();

  /* Optional: Display current status */
  displaySensorStatus();

  bno.setExtCrystalUse(true);

  pinMode(ledPin, OUTPUT); // This is used for testing.

  Wire.begin(SLAVE_ADDRESS); // Set up the Wire library and make Arduino the slave
  
  /* Define the callbacks for i2c communication */
  Wire.onReceive(processMessage); // Used to specify a function when data received from Master
  Wire.onRequest(sendIMUReading); // Used to specify a function when the Master requests data
  
}

/**************************************************************************/
/*
    Arduino loop function, called once 'setup' is complete
*/
/**************************************************************************/
void loop(void)
{

  while (!done) {
    /* Get a new sensor event */
    sensors_event_t event;
    bno.getEvent(&amp;event);

    /* Display the floating point data */
    Serial.print("Yaw: ");
    yaw = (int) event.orientation.x;
    Serial.print(yaw);
    if (yaw < 0) {
      imu_data[8] = 1;  // Capture the sign information
      yaw = abs(yaw);
    }
    else {
      imu_data[8] = 0;
    }
    if (yaw > 360) {
      yaw = yaw - 360; // Calculate equivalent angle
    } 
    
    Serial.print("\tPitch: ");
    pitch = (int) event.orientation.y;
    Serial.print(pitch);
    if (pitch < 0) {
      imu_data[4] = 1;   // Capture the sign information
      pitch = abs(pitch);
    }
    else {
      imu_data[4] = 0;
    }
    
    Serial.print("\tRoll: ");
    roll = (int) event.orientation.z; 
    Serial.print(roll);
    if (roll < 0) {
      imu_data[0] = 1;    // Capture the sign information
      roll = abs(roll);
    }    
    else {
      imu_data[0] = 0;
    }

    /* Optional: Display calibration status */
    displayCalStatus();

    /* Optional: Display sensor status (debug only) */
    //displaySensorStatus();

    /* New line for the next sample */
    Serial.println("");

    /* Update the IMU data by extracting each digit from the raw data */
    imu_data[1] = getDigit(roll, 2);
    imu_data[2] = getDigit(roll, 1);
    imu_data[3] = getDigit(roll, 0);
    imu_data[5] = getDigit(pitch, 2);
    imu_data[6] = getDigit(pitch, 1);
    imu_data[7] = getDigit(pitch, 0);
    imu_data[9] = getDigit(yaw, 2);
    imu_data[10] = getDigit(yaw, 1);
    imu_data[11] = getDigit(yaw, 0);

    /* Wait the specified delay before requesting nex data */
    delay(BNO055_SAMPLERATE_DELAY_MS);

    end_program();

  }
         
  // Do nothing
  while (true){};

}

Here is the code for the I2C Python program on the Raspberry Pi, responsible for sending messages and requesting IMU data via I2C from the Arduino slave:

import smbus
import time
# Created by Addison Sears-Collins
# April 17, 2019
# Open a new file to log the IMU data
f = open("imu_data.txt", "w")

# for RPI version 1, use bus = smbus.SMBus(0)
bus = smbus.SMBus(1)

# This is the address we setup in the Arduino Program
SLAVE_ADDRESS = 0x04

def request_reading():
  # Read a block of 12 bytes starting at SLAVE_ADDRESS, offset 0
  reading = bus.read_i2c_block_data(SLAVE_ADDRESS, 0, 12)

  # Extract the IMU reading data
  if reading[0] < 1:
    roll_sign = "+"
  else:
    roll_sign = "-"
  roll_1 = reading[1]
  roll_2 = reading[2]
  roll_3 = reading[3]

  if reading[4] < 1:
    pitch_sign = "+"
  else:
    pitch_sign = "-"    
  pitch_1 = reading[5]
  pitch_2 = reading[6]
  pitch_3 = reading[7]

  if reading[8] < 1:
    yaw_sign = "+"
  else:
    yaw_sign = "-" 
  yaw_1 = reading[9]
  yaw_2 = reading[10]
  yaw_3 = reading[11]

  # Print the IMU data to the console
  print("Roll: " + roll_sign + str(roll_1) + str(roll_2) + str(roll_3) +
        "   Pitch: " + pitch_sign + str(pitch_1) + str(pitch_2) + str(pitch_3) +
        "   Yaw: " + yaw_sign + str(yaw_1) + str(yaw_2) + str(yaw_3))

  try:
    f.write("Roll: " + roll_sign + str(roll_1) + str(roll_2) + str(roll_3) +
        "   Pitch: " + pitch_sign + str(pitch_1) + str(pitch_2) + str(pitch_3) +
        "   Yaw: " + yaw_sign + str(yaw_1) + str(yaw_2) + str(yaw_3) + "\n")
  except(KeyboardInterrupt, SystemExit):
    f.close()

# Request IMU data every 5 seconds from the Arduino
while True:
  # Used for testing: command = raw_input("Enter command: l - toggle LED, r - read IMU ")
    # if command == 'l' :
    #   bus.write_byte(SLAVE_ADDRESS, ord('l'))
    # elif command == 'r' :
  request_reading()
  time.sleep(5)

Video