How to send multiple variables from Processing to Arduino

Categories Interaction, Programming

I wanted to be able to send a set of 4 integers to an Arduino from a Processing application that I am working on, I also wanted to be able to prefix the set with a tag, so that I could deal with different sets of integers in specific ways, for specific purposes.

For instance, I have an LCD screen and some LED’s connected to my Arduino, or maybe I have a servo motor and a speaker that I want to control based on events happening in software running via Processing.

I modified* the code below from the code shown here (Arduino Cookbook @ inkling.com)

*I simply expanded the amount of variables being sent per packet.

Processing Code:

// Processing Sketch

/* SendingBinaryToArduino
 * Language: Processing
 */
import processing.serial.*;

Serial myPort;  // Create object from Serial class
public static final char HEADER    = 'H';
public static final char A_TAG = 'M';
public static final char B_TAG = 'X';

void setup()
{
  size(512, 512);
  String portName = Serial.list()[1];
  myPort = new Serial(this, portName, 9600);
}

void draw(){
}

void serialEvent(Serial p) {
  // handle incoming serial data
  String inString = myPort.readStringUntil('\n');
  if(inString != null) {     
    print( inString );   // echo text string from Arduino
  }
}

void mousePressed() {
  sendMessage(A_TAG, 8,5,20,33);
}

void sendMessage(char tag, int a, int b, int c, int d){
  // send the given index and value to the serial port
  myPort.write(HEADER);
  myPort.write(tag);
  myPort.write((char)(a / 256)); // msb
  myPort.write(a & 0xff);  //lsb
  myPort.write((char)(b / 256)); // msb
  myPort.write(b & 0xff);  //lsb
  myPort.write((char)(c / 256)); // msb
  myPort.write(c & 0xff);  //lsb
  myPort.write((char)(d / 256)); // msb
  myPort.write(d & 0xff);  //lsb
}

You can see in the void sendMessage function that each integer is being split into two bytes, but both the header and tag are sent as a single byte – this means we are sending 10 bytes all up (we will need to reference this in the Arduino code in TOTAL_BYTES).

Arduino Code:

// BinaryDataFromProcessing
// These defines must mirror the sending program:
const char HEADER       = 'H';
const char A_TAG    = 'M';
const char B_TAG    = 'X';
const int  TOTAL_BYTES  = 10  ; // the total bytes in a message

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

void loop(){
  if ( Serial.available() >= TOTAL_BYTES)
  {
     if( Serial.read() == HEADER)
    {
      char tag = Serial.read();
      if(tag == A_TAG)
      {
        //Collect integers
        int a = Serial.read() * 256; 
        a = a + Serial.read();
        int b = Serial.read() * 256;
        b = b + Serial.read();
        int c = Serial.read() * 256;
        c = c + Serial.read();
        int d = Serial.read() * 256;
        d = d + Serial.read();
        Serial.print("Received integers | a:");
        Serial.print(a);
        Serial.print(", b:");
        Serial.println(b);
        Serial.print(", c:");
        Serial.println(c);
        Serial.print(", d:");
        Serial.println(d);
      }
      else {
        Serial.print("got message with unknown tag ");
        Serial.write(tag);
      }
    }
  }
}

You can see under Serial.available() after the comment “//Collect integers” that each byte is being stored in a variable (multiplied by 256 to reverse the division on the Processing side) and then the second byte is added to that (thus reversing the rejoining the split that took place on the Processing side) – in this way we are reassembling the data that we sent into a useable format to be used.

From here you can do whatever you like with the data, use it for conditionals or set it to analog outputs. The applications are nearly endless.

Drawing in Python using Arduino data via serial

Categories Open-source, Programming, Visuals

Following on from my previous post where I established serial communication between an Arduino and a Raspberry Pi, I needed to find out if I could store the data being sent from the Arduino in a variable on the Raspberry Pi and use it to alter some functions in a Python script.

I wrote up a piece of code that tries to read the data from the serial and use it to change the colour of a circle drawn in the center of a 640 x 480 pixel screen:

# Title: Arduino2RPiSerial
 #
 # Goal: to draw a circle based on colour values sent from the arduino
 #

import pygame
 import sys
 import serial

pygame.init()

#create a screen
 screen = pygame.display.set_mode((640,480))

#create colour
 redValue = 255
 fgColour = (redValue,0,0)
 bgColour = (0,0,255)

screen.fill(bgColour)

#serial(device,baud)
 ser = serial.Serial('/dev/ttyACM0',9600)

# LOOP
 while 1 :

#Update from serial
 redValue = ser.readline()
 #update colour value
 fgColour = (redValue,0,0)
 pygame.draw.circle(screen, fgColour, (320,240), 200, 0)
 pygame.display.update()
 pygame.time.delay(5)

# check for quit events
 for event in pygame.event.get():
 if event.type == pygame.QUIT:
 pygame.quit(); sys.exit();

Getting the Raspberry Pi to talk to Arduino

Categories Open-source, Programming

As part of an exploratory design project I am undertaking within my undergraduate Major Project, I needed to establish serial communication between a Raspberry Pi (a miniature, credit-card sized computer) and an Arduino Uno (an electronic prototyping board). I found that Raspberry Pi could both supply power and talk to the Arduino Uno via USB cable.

I also found that as a beginner in many aspects of Python programming, Linux commands and serial communication that much of the documentation on the internet seemed daunting, so I’ve made a very thorough documentation here to help anyone out who has the same amount or less of the starting knowledge that I had. Hopefully it can aid in the creation of more open-source Raspberry Pi / Arduino projects.

I based my efforts on the steps outlined here.

 

 

 

Arduino Uno, Raspberry Pi and Laptop.
Arduino Uno connected to the laptop, with  a Raspberry Pi bundled with it’s own 3.5″ LCD Screen running below.

 

Firstly, I needed to install pyserial onto my Raspberry Pi. I have no ethernet cable or Wi-Fi dongle connected to my Raspberry Pi and so I had to transfer the pyserial-2.6.tar file via a USB Flash drive. The file can be downloaded here.

After transferring the file to desktop (home/pi/desktop) and unzipping it’s contents to it’s own folder on the desktop (home/pi/desktop/pyserial-2.6) I opened up the LXterminal to execute the following commands:

cd /home/pi/desktop/pyserial-2.6

The cd command directs the terminal to a folder on the Raspberry Pi (in this case, the desktop), to give future commands a context of operation. Basically, the command tells the terminal where we are working from and where to look for any files called upon.

Next:

sudo python setup.py install

This command tells python to install pyserial. I hit enter and the terminal spat out line after line of output, completing the install process shortfly after.

From this point, the Raspberry Pi was ready for serial communication via the pyserial module.

I needed to find out what the device name for the Arduino Uno was on the Raspberry Pi so that I could reference it in the python shell when opening up serial communications. For this I used a command that lists the devices:

ls /dev/tty*

The ls command lists files within a directory, the second part ‘/dev/tty*’ is a filter. The use of the wildcard character ‘*’ means that we are looking for any files that begin with ‘/dev/tty’ and that end with any other combination of characters. I ran the command without the Arduino Uno connected and then again with the Arduino Uno connected so that I could see the difference between the two lists, and find out what it’s device name was.

 

 

 

Using ls /dev/tty* to display a list of devices
Using ls /dev/tty* to display a list of devices

 

It’s hard to see in the picture above because the 3.5″ TFT LCD screen has such a horrible resolution (and has a strange flickering colour issue) but in the second list positioned at 3 items from the bottom of the rightmost column, a file appeared that wasn’t present in the first list (/dev/ttyACM0). I made note of that file because I would need to reference it later.

Then, the code below needed to be uploaded to the Arduino Uno to generate a test signal:

//Code originally by simon monk (http://www.doctormonk.com/2012/04/raspberry-pi-and-arduino.html)
//Commented by Daniel Kerris

//This code makes use of the Arduino's built-in LED which is located on Pin 13
const int ledPin = 13;

 //This sets up the code and defines the baud rate as 9600 - it's important to use the same baud rate on the Raspberry Pi
 void setup()
 {
   pinMode(ledPin, OUTPUT);
   Serial.begin(9600);
 }

 //This part of the code loops continuously with a delay of 1000 milliseconds between each loop
 //It sends the message "Hello Pi" over and over again via USB
 void loop()
 {
   Serial.println("Hello Pi");

   //This section checks to see if the Raspberry Pi is talking back
   //and then makes a call to the flash() script which is define below
   if (Serial.available())
   {
      flash(Serial.read() - '0');
   }
   delay(1000);
 }

 //This flash() script takes the number that the Raspberry Pi has sent over via USB (stored in the variable n)
 //and uses it to determing how many times the LED should flash
 void flash(int n)
 {
   for (int i = 0; i < n; i++)
   {
     digitalWrite(ledPin, HIGH);
     delay(100);
     digitalWrite(ledPin, LOW);
     delay(100);
   }
 }

After the code was uploaded to the Arduino Uno, I connected it via USB to the Raspberry Pi. I could see that it was powered and that the code was working because the LED for Tx (serial communication) was flashing, showing that it was being used. The Raspberry Pi still needed some code to tell it to listen to the messages coming through the USB port.

I booted up the Raspberry Pi and opened up the application called IDLE, highlighted the Python Shell Window and entered the following commands, hitting enter after each line:

import serial
ser = serial.Serial('/dev/ttyACM0', 9600)

You’ll remember that ‘/dev/ttyACM0’ was the name of the Arduino that I had found out earlier. 9600 is the baud rate, which is set the same is in the Arduino code above.

Then:

while 1 :
     ser.readline()

The while statment is used to do a set of actions while a statement is true. In computer languages 1 and 0 are stand-ins for true and false or on and off. Basically, this line of code is saying that whilst 1 is equal to true (which is constantly) then do something. This creates a loop that executes itself until the program quits, just like the void loop() in the above Arduino code. The ser.readline() is telling our serial object ser that we want to execute the function readline() which reads from the serial device (‘/dev/ttyACM0′) that we established earlier.

I had to hit enter twice after the ser.readline() command to let Python know that I am finished writing commands within the while statement’s block (you can read more about code blocks here if you don’t understand).

 

 

Success!
Success!

 

Finally, the Raspberry Pi successfully read from the Arduino.

I couldn’t get return communication happening successfully, though luckily for me the project I am working on only requires one-way communication from Arduino Uno to Raspberry Pi and not the other way round. I’m going to be using the Arduino Uno to handle sensors and tangible controls as I am much more comfortable coding and prototyping in that environment. I will write code that analyses and packages the information from sensors and tangible controls and sends it via USB to the Raspberry Pi, which will handle all of the GUI and Sound output (which the Arduino would otherwise struggle to handle).