In this post, I’ll show you how to configure your Raspberry Pi so that your programs can run as soon as you plug in your Raspberry Pi to a power source.
Requirements
Here are the requirements:
Run a program as soon as the Raspberry Pi is turned on.
Directions
Power up your Raspberry Pi, and open up a terminal window.
Type:
sudo nano /etc/rc.local
Scroll down the file to the area right after fi but before exit 0. Type:
python3 /home/pi/robot/ball_following_yellow.py &
The format is
python3 /your/file/path/here/filename.py &
Press CTRL-X, and save the file.
Restart your Raspberry Pi.
sudo reboot
Your program, ball_following_yellow.py, should run on startup.
Special shout out to Matt Timmons-Brown for this project idea. He is the author of a really good book on Raspberry Pi robotics: (Learn Robotics with Raspberry Pi). Go check it out!
Video
Here is a video of what we will build in this tutorial.
Requirements
Here are the requirements:
Build a line-following robot using Raspberry Pi.
You Will Need
The following components are used in this project. You will need:
These sensors have an infrared (IR) receiver and transmitter.
Black things (e.g. black electrical tape) absorb IR light; white things (e.g. white poster board) reflect IR light.
The receiver will not be able to detect IR light emitted by the transmitter when the robot is over the black electrical tape. Output (OUT pin) of the sensor will be LOW.
The receiver will detect IR light emitted (and then reflected) by the transmitter when the robot is on top of the white poster board because the white poster board will reflect the IR light (black will absorb the IR light). The output (OUT pin) of the sensor will go HIGH.
The robot will use the information provided by this sensor to steer itself and follow the black electrical tape line.
Connect the VCC pin of the IR line sensor to pin 1 of the Raspberry Pi.
Connect the GND pin of the line sensor to the blue (negative) ground rail of the solderless breadboard.
Connect the OUT pin of the line sensor to pin 21 (GPIO 9) of the solderless breadboard.
Testing the Infrared Line Sensor
Power up your Raspberry Pi, and open IDLE.
Create a new program called test_line_following.py.
Save it in to your robot directory.
Here is the code:
import gpiozero
import time
# Description: Code for testing the
# TCRT5000 IR Line Track Follower Sensor
# Author: Addison Sears-Collins
# Date: 05/29/2019
# Initialize line sensor to GPIO9
line_sensor = gpiozero.DigitalInputDevice(9)
while True:
if line_sensor.is_active == False:
print("Line detected")
else:
print("Line not detected")
time.sleep(0.2) # wait for 0.2 seconds
Create a line-following course using your black electrical tape and your poster board. It should look something like this.
I recommend leaving a 3-inch margin between the side of the poster board and the course. Don’t make curves that are too sharp.
Run your test program from a terminal window.
cd robot
python3 test_line_following.py
Move your track in front of the sensor to see if the terminal prints out “Line detected. “
If you are running into issues, use a screwdriver to adjust the sensitivity of the sensor.
That white and blue potentiometer is what you should tweak.
Connect the other IR line sensor.
Connect the VCC pin of the IR line sensor to pin 17 of the Raspberry Pi using a female-to-female jumper wire.
Connect the GND pin of the IR line sensor to the blue (negative) ground rail of the solderless breadboard.
Connect the OUT pin of the IR line sensor to pin 23 (GPIO 11) of the Raspberry Pi.
Attaching the Sensors
Attach the first IR line sensor you wired up to the front, left side of the robot.
Attach the second IR line sensor to the right side of the robot.
Both sensors need to be just off the ground and can be mounted using 2×2 Lego blocks that extend downward from the body of the robot.
A piece of VELCRO is sufficient to attach both sensors.
Run the wires connected to the IR line sensors down through the gap in the robot body.
Create the Line-Following Program in Python
Open IDLE on your Raspberry Pi.
Create a new file inside your robot directory named
line_following_robot.py
Here is the code:
import gpiozero
# File name: line_following_robot.py
# Code source (Matt-Timmons Brown): https://github.com/the-raspberry-pi-guy/raspirobots
# Date created: 5/29/2019
# Python version: 3.5.3
# Description: Follow a line using a TCRT5000 IR
# Line Following Sensor
robot = gpiozero.Robot(left=(22,27), right=(17,18))
left = gpiozero.DigitalInputDevice(9)
right = gpiozero.DigitalInputDevice(11)
while True:
if (left.is_active == True) and (right.is_active == True):
robot.forward()
elif (left.is_active == False) and (right.is_active == True):
robot.right()
elif (left.is_active == True) and (right.is_active == False):
robot.left()
else:
robot.stop()
Deploying Your Line-Following Robot
Place your robot on your track. Make sure the line-following sensors are directly above the black line.
Verify that your Raspberry Pi is connected to battery power, and your 4xAA battery pack is turned on.
Run your program from inside the robot directory.
cd robot
python3 line_following_robot.py
Watch your robot follow the line! Press CTRL-C anytime to stop the program.
In this post, I will show you how to add light to a Raspberry Pi wheeled robot.
Special shout out to Matt Timmons-Brown for this project idea. He is the author of a really good book on Raspberry Pi robotics: (Learn Robotics with Raspberry Pi). Go check it out!
Requirements
Here are the requirements:
Add lights to a wheeled robot using the Adafruit NeoPixel Stick with 8 RGB LEDs.
You Will Need
The following components are used in this project. You will need:
Cut four pins off one of the male pin header connectors with a pair of scissors.
Solder the four pins to the DIN (stands for “data-in”) side of the RGB LED stick.
If you don’t know how to solder, check out my video below.
Connect the 5VDC pin of the RGB LED stick to the positive (red) 5V rail of the solderless breadboard.
Connect the GND (Ground) pin of the RGB LED stick to the blue (negative) rail of the solderless breadboard.
Connect the DIN pin of the RGB LED stick to pin 19 (GPIO 10) of the Raspberry Pi. This is the Master Output Slave Input (MOSI) pin that the Pi uses to send information out via the SPI protocol (more on this in a second).
Mount the RGB LED on the Robot using Velcro. You can mount it anywhere you want.
Power up your Raspberry Pi.
Open a terminal window.
Verify that pip is installed. Pip is a tool that enables you to install and manage libraries that are not a part of Python’s standard library. Type the following commands in the terminal window.
sudo apt-get update
sudo apt-get install python3-pip
Install the rpi_ws 281x library.
sudo pip3 install rpi_ws281x
Make sure the SPI bus is enabled.
SPI is a communication interface built-in to several of the GPIO pins of the Raspberry Pi. It is good to use the SPI bus when you want data to be streamed over short distances, continuously with no interruptions.
Type this terminal command:
sudo raspi-config
Interfacing Options → SPI
Select Yes
Finish
Reboot the Raspberry Pi.
sudo reboot
Wait for the Raspberry Pi to reboot, then open a terminal window again in Raspberry Pi (I’m using Putty).
Modify the Graphics Programming Unit core frequency so that it is 250 MHz.
sudo nano /boot/config.txt
Scroll down, and add this to the bottom of the file.
core_freq = 250
CTRL-X –> Y –> ENTER to save
Reboot the Raspberry Pi.
sudo reboot
Testing the rpi_ws281x Library
Open IDLE on your Raspberry Pi.
Create a new file.
Save it as rgb_library_test.py
Type the following code:
#!/usr/bin/env python3
# NeoPixel library strandtest example
# Author: Tony DiCola (tony@tonydicola.com)
#
# Direct port of the Arduino NeoPixel library strandtest example. Showcases
# various animations on a strip of NeoPixels.
# Code source (Matt-Timmons Brown): https://github.com/the-raspberry-pi-guy/raspirobots
# Minor edits by Matt Timmons-Brown for "Learn Robotics with Raspberry Pi"
import time
from rpi_ws281x import *
import argparse
# LED strip configuration:
LED_COUNT = 8 # Number of LED pixels.
#LED_PIN = 18 # GPIO pin connected to the pixels (18 uses PWM!).
LED_PIN = 10 # GPIO pin connected to the pixels (10 uses SPI /dev/spidev0.0).
LED_FREQ_HZ = 800000 # LED signal frequency in hertz (usually 800khz)
LED_DMA = 10 # DMA channel to use for generating signal (try 10)
LED_BRIGHTNESS = 255 # Set to 0 for darkest and 255 for brightest
LED_INVERT = False # True to invert the signal (when using NPN transistor level shift)
LED_CHANNEL = 0 # set to '1' for GPIOs 13, 19, 41, 45 or 53
LED_STRIP = ws.WS2811_STRIP_GRB # Strip type and color ordering
# Define functions which animate LEDs in various ways.
def colorWipe(strip, color, wait_ms=50):
"""Wipe color across display a pixel at a time."""
for i in range(strip.numPixels()):
strip.setPixelColor(i, color)
strip.show()
time.sleep(wait_ms/1000.0)
def theaterChase(strip, color, wait_ms=50, iterations=10):
"""Movie theater light style chaser animation."""
for j in range(iterations):
for q in range(3):
for i in range(0, strip.numPixels(), 3):
strip.setPixelColor(i+q, color)
strip.show()
time.sleep(wait_ms/1000.0)
for i in range(0, strip.numPixels(), 3):
strip.setPixelColor(i+q, 0)
def wheel(pos):
"""Generate rainbow colors across 0-255 positions."""
if pos < 85:
return Color(pos * 3, 255 - pos * 3, 0)
elif pos < 170:
pos -= 85
return Color(255 - pos * 3, 0, pos * 3)
else:
pos -= 170
return Color(0, pos * 3, 255 - pos * 3)
def rainbow(strip, wait_ms=20, iterations=1):
"""Draw rainbow that fades across all pixels at once."""
for j in range(256*iterations):
for i in range(strip.numPixels()):
strip.setPixelColor(i, wheel((i+j) & 255))
strip.show()
time.sleep(wait_ms/1000.0)
def rainbowCycle(strip, wait_ms=20, iterations=5):
"""Draw rainbow that uniformly distributes itself across all pixels."""
for j in range(256*iterations):
for i in range(strip.numPixels()):
strip.setPixelColor(i, wheel((int(i * 256 / strip.numPixels()) + j) & 255))
strip.show()
time.sleep(wait_ms/1000.0)
def theaterChaseRainbow(strip, wait_ms=50):
"""Rainbow movie theater light style chaser animation."""
for j in range(256):
for q in range(3):
for i in range(0, strip.numPixels(), 3):
strip.setPixelColor(i+q, wheel((i+j) % 255))
strip.show()
time.sleep(wait_ms/1000.0)
for i in range(0, strip.numPixels(), 3):
strip.setPixelColor(i+q, 0)
# Main program logic follows:
if __name__ == '__main__':
# Process arguments
parser = argparse.ArgumentParser()
parser.add_argument('-c', '--clear', action='store_true', help='clear the display on exit')
args = parser.parse_args()
# Create NeoPixel object with appropriate configuration.
strip = Adafruit_NeoPixel(LED_COUNT, LED_PIN, LED_FREQ_HZ, LED_DMA, LED_INVERT, LED_BRIGHTNESS, LED_CHANNEL)
# Intialize the library (must be called once before other functions).
strip.begin()
print ('Press Ctrl-C to quit.')
if not args.clear:
print('Use "-c" argument to clear LEDs on exit')
try:
while True:
print ('Color wipe animations.')
colorWipe(strip, Color(255, 0, 0)) # Red wipe
colorWipe(strip, Color(0, 255, 0)) # Blue wipe
colorWipe(strip, Color(0, 0, 255)) # Green wipe
print ('Theater chase animations.')
theaterChase(strip, Color(127, 127, 127)) # White theater chase
theaterChase(strip, Color(127, 0, 0)) # Red theater chase
theaterChase(strip, Color( 0, 0, 127)) # Blue theater chase
print ('Rainbow animations.')
rainbow(strip)
rainbowCycle(strip)
theaterChaseRainbow(strip)
except KeyboardInterrupt:
if args.clear:
colorWipe(strip, Color(0,0,0), 10)
Save it.
Open a new terminal window.
Run the test using the following command:
python3 rgb_library_test.py -c
The -c at the end makes sure that the RGB LEDs turn off when you type CTRL-C in the terminal window.
Managing the RGB LEDs Using the Nintendo Wii Remote Control
Now we will create a program to control the LEDs using our Wii remote. Open a new terminal window on your Raspberry Pi, and go to the robot directory.
cd robot
Open a new file in IDLE named rgb_wii_remote.py
Type the following code into the program:
import gpiozero
import cwiid
import time
from rpi_ws281x import *
# Author: Matt Timmons-Brown for "Learn Robotics with Raspberry Pi"
# Description: Enables control of the LED with the Wii Remote
# Minor modifications made by Addison Sears-Collins
robot = gpiozero.Robot(left=(22,27), right=(17,18))
print("Press and hold the 1+2 buttons on your Wiimote simultaneously")
wii = cwiid.Wiimote()
print("Connection established")
wii.rpt_mode = cwiid.RPT_BTN | cwiid.RPT_ACC
LED_COUNT = 8
LED_PIN = 10
LED_FREQ_HZ = 800000
LED_DMA = 10
LED_BRIGHTNESS = 150
LED_INVERT = False
LED_CHANNEL = 0
LED_STRIP = ws.WS2811_STRIP_GRB
strip = Adafruit_NeoPixel(LED_COUNT, LED_PIN, LED_FREQ_HZ, LED_DMA, LED_INVERT, LED_BRIGHTNESS, LED_CHANNEL, LED_STRIP)
strip.begin()
def colorWipe(strip, color, wait_ms=50):
"""Wipe color across display a pixel at a time."""
for i in range(strip.numPixels()):
strip.setPixelColor(i, color)
strip.show()
time.sleep(wait_ms/1000.0)
while True:
buttons = wii.state["buttons"]
if (buttons & cwiid.BTN_PLUS):
colorWipe(strip, Color(255, 0, 0)) # Red wipe
if (buttons & cwiid.BTN_HOME):
colorWipe(strip, Color(0, 255, 0)) # Blue wipe
if (buttons & cwiid.BTN_MINUS):
colorWipe(strip, Color(0, 0, 255)) # Green wipe
if (buttons & cwiid.BTN_B):
colorWipe(strip, Color(0, 0, 0)) # Blank
x = (wii.state["acc"][cwiid.X] - 95) - 25
y = (wii.state["acc"][cwiid.Y] - 95) - 25
if x < -25:
x = -25
if y < -25:
y = -25
if x > 25:
x = 25
if y > 25:
y = 25
forward_value = (float(x)/50)*2
turn_value = (float(y)/50)*2
if (turn_value < 0.3) and (turn_value > -0.3):
robot.value = (forward_value, forward_value)
else:
robot.value = (-turn_value, turn_value)
Save the program.
Place your robot in an open space, and run the following command from inside your Pi’s robot directory.
python3 rgb_wii_remote.py
You can press the home, minus, and plus buttons to activate different lights.
Turn off the lights using the B button, and stop the program by typing CTRL-C.
