3-Axis Accelerometer and Processing _ Robot is Happy

3/27/2014 3-Axis Accelerometer and Processing | Robot is Happy

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Part 1) Visualizing 3-Axis Accelerometer Readings in Processingby Christopher Hazlett

It's been a while since I've had the chance to do anything vaguely electronic. Sure, I've painted rooms in my house,installed ceiling fans, added insulation to my attic, but that's a far cry from programming in Wiring or Processing. So,thankfully, after getting my new workspace all put together, I got the chance to play with some of the parts I've had waitingin a few SparkFun boxes.

So I started playing around with a 3-Axis Accelerometer in the hopes of dreaming up some project or other. So I hooked itup to my Arduino and my Arduino to my computer and wrote a little Processing code to graph it all into pretty colors. Aswith all of my projects, the first step for me is understanding and since I didn't have much experience with Accelerometersa little crash course was in order. As it turns out, it's a fairly simple sensor to use (or collection of 3 sensors: x, y, z, Ishould say). Simply plug the VCC connector into the Arduino 3V pin (not the 5V pin. The ADXL3305 chip is only rated to3.3V), the ground into ground and the x, y, and z pins into 0,1,2 analog pins. The code for the Arduino is simple:

The Arduino Code

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#define X_AXIS 0

#define Y_AXIS 1

#define Z_AXIS 2

void setup() {

Serial.begin(9600);

}

void loop() {

int x = analogRead(X_AXIS);

int y = analogRead(Y_AXIS);

int z = analogRead(Z_AXIS);

Serial.print(x);

Serial.print('|');

Serial.print(y);

Serial.print(':');

Serial.println(z);

}

It takes the readings in and outputs them into a formatted string '[x]|[y]:[z]'. That's it. This is just for outputting data rightnow, so nothing special. It gets more interesting when we look at the processing.

The Processing Code in Action

The code that makes the sweet, sweet video above isn't necessarily complicated, but there may be a few things you haven't

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The code that makes the sweet, sweet video above isn't necessarily complicated, but there may be a few things you haven'tused in Processing before.

map(value, low1, high1, low2, high2) - converts a value from one range into a corresponding value into another

range.

norm(value, low, high) - converts a value into a value from 0.0 to 1.0 based on the supplied range.

pushMatrix() / popMatrix() - the pushMatrix() and popMatrix() methods allow you to apply rotation, translation, and

other methods to a specific style. By issuing the pushMatrix() then calling the translate(), and rotateX, rotateY

methods, you can then call popMatrix so those methods don't affect other elements being rendered by Processing.

The Processing Code

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import processing.serial.*;

import processing.opengl.*;

Serial myPort;

int baudRate = 9600;

int lf = 10;

PFont font;

int[] xAxis;

int[] yAxis;

int[] zAxis;

int currentX = 0;

int currentY = 0;

int currentZ = 0;

//these value were determined by taking readings from a resting position

int oneGSensorValue = 400;

float oneGMillivolt = oneGSensorValue * 4.9;

int totalReadings = 400;

int readingPos = 0; // the reading position in the array

void setup(){

smooth();

size(600, 300, OPENGL);

font = createFont(PFont.list()[270], 24);

smallFont();

xAxis = new int[totalReadings];

yAxis = new int[totalReadings];

zAxis = new int[totalReadings];

for (int i=0; i < totalReadings; i++){

xAxis[i] = oneGSensorValue;

yAxis[i] = oneGSensorValue;

zAxis[i] = oneGSensorValue;

}

myPort = new Serial(this, Serial.list()[0], baudRate);

myPort.bufferUntil(lf);

noLoop();

}

void serialEvent(Serial p){

String inString;

try{

inString = (myPort.readString());

currentX = xValue(inString);

currentY = yValue(inString);

currentZ = zValue(inString);

xAxis = insertValueIntoArray(xAxis, currentX, readingPos, totalReadings);

yAxis = insertValueIntoArray(yAxis, currentY, readingPos, totalReadings);

zAxis = insertValueIntoArray(zAxis, currentZ, readingPos, totalReadings);

readingPos = readingPos + 1; // increment the array position

}catch(Exception e){

println(e);

}

redraw();

}

void draw()

{

background(#FEFFFC);

drawGraph(xAxis, 100, color(#519050), "X - Axis");

drawGraph(yAxis, 200, color(#708CDE), "Y - Axis");

drawGraph(zAxis, 300, color(#D38031), "Z - Axis");

draw3d(currentX, currentY, currentZ);

}

void drawGraph(int[] arrToDraw, int yPos, color graphColor, String name){

int arrLength = arrToDraw.length;

stroke(graphColor);

for (int x=0; x



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}

pushStyle();

smallFont();

stroke(#FFFFFF);

fill(#FFFFFF);

String gString = nfc(gFromSensorValue(arrToDraw[arrLength - 2]), 2);

text(name + " : " + gString + " Gs", 10, yPos - 10);

popStyle();

}

void draw3d(int currentX, int currentY, int currentZ){

float normalizedX = norm(currentX, 0.0, 700.0);

float normalizedY = norm(currentY, 0.0, 700.0);

float normalizedZ = norm(currentZ, 0.0, 700.0);

float finalZ = map(normalizedZ, 0.0, 1.0, 300.00, 0.0);

float finalY = map(normalizedY, 0.0, 1.0, -3.5, 3.5);

float finalX = map(normalizedX, 0.0, 1.0, -3.5, 3.5);

pushMatrix();

ambientLight(102, 102, 102);

lightSpecular(204, 204, 204);

directionalLight(102, 102, 102, -1, -1, -1);

shininess(1.0);

translate(500, finalZ);

rotateY(finalY + 1.0);

rotateZ(finalX);

fill(#E2E8D5);

noStroke();

fill(#B76F6F);

float heightWidth = finalX * 1.8;

box(65, 65, 50);

popMatrix();

}

int xValue(String inString){

int pipeIndex = inString.indexOf('|');

return int(inString.substring(0,pipeIndex));

}

int yValue(String inString){

int pipeIndex = inString.indexOf('|');

int colonIndex = inString.indexOf(':');

return int(inString.substring(pipeIndex+1, colonIndex));

}

int zValue(String inString){

int colonIndex = inString.indexOf(':');

return int(inString.substring(colonIndex + 1, inString.length() - 2));

}

/*

This little method creates a running tally of all the incoming sensor readings

and then, when it reaches the end of the array, it pops the first one of the beginning

and inserts a new value in at the end...thus keeping a running tally of the last 400

readings (it can be for any length array, that's just what it's set to for this project).

This works a lot like an RRD graph where my inspiration came from.

*/

int[] insertValueIntoArray(int[] targetArray, int val, int pos, int maxLength){

if(pos > (maxLength-1)){

// if the pos == maxSize, shift the array to retain the original value

int[] returnArray = subset(targetArray, 1, maxLength-1);

returnArray = expand(returnArray, maxLength);

returnArray[maxLength-2] = val;

return returnArray;

}else{

targetArray[pos] = val;

return targetArray;

}

}

/*

This conversion will vary from project to project

and if you're project is relying on battery power

the reading may need to be adjusted to give you true

one G as your battery power decreases. All of this is due to

the output of the X,Y, and Z sensors and their coorelation to the incoming voltage at VCC

Check out the specs for the ADXL335 (part of the break out board from Sparkfun.com) here:

http://www.analog.com/en/sensors/inertial-sensors/adxl335/products/product.html

*/

float gFromSensorValue(int sensorValue){

//convert analog value into millivolts

float mvValue = sensorValue * 4.9;

return mvValue/oneGMillivolt;

}

void smallFont(){ textFont(font, 24); }

void mediumFont(){ textFont(font, 30); }

void largeFont(){ textFont(font, 40); }

This is just the first step of a larger project to create a DIY radio control using an xBee and this 3-axis accelerometer.



About Christopher HazlettChris has been programming for almost a decade, and thinks programming is even more fun whenit makes a robot do stuff...even if that stuff is just a bunch of blinking lights. Chris's GIT repos:http://github.com/chazlett.

Tagged as: Accelerometer, Arduino, Processing Leave a comment

RichardFebruary 11th, 2011 - 14:02

Thanks for the code and video got it working!Cheers!

DanOctober 17th, 2011 - 12:46

Hmm cant seem to get the code to work.Is the code specific for running on a MAC or will it work for Windows XP as well?

DanOctober 19th, 2011 - 12:09

Got it working! I finally realized I need to tell it what COM port to use inside the [].Anyway thanks for the code. This is a great learning resource!

Stuff Im Researching for a Project Finally, Back to Work

This is just the first step of a larger project to create a DIY radio control using an xBee and this 3-axis accelerometer.

Happy Coding.- Chris

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3-Axis Accelerometer and Processing _ Robot is Happy