Drawing of graphs from I2C IMU

dragal

Hello guys here is my code. I have tried to draw 3 graphs from arduino. I am reading angle by meaning inegration gyro angle , accelerometer angle and their complementary filter. But i get the message "Error, disabling serialEvent() for COM5 null"

import processing.serial.*;
Serial port;
float currentAngle ;
float pitchacc ;
float pitch ;
int gyro = 1;
int accel = 2;
int xn = 0;
float yn1 = 250;
float yn2 = 250;
float yn3 = 250;
int xk = 0; 
void setup ()
{
  size (500,500);
  background (0);  
  port = new Serial ( this, "COM5", 9600);
  port.bufferUntil ('\n');
}
void draw ()
{ 
fill(255); 
stroke(255); 
line (xn, yn1, xk, currentAngle); 
line (xn, yn2, xk, pitchacc); 
line (xn, yn3, xk, pitch); 
if (xk > 500) {  
background(0);  
xk=0;   
}      
xn=xk; 
yn1 = currentAngle;
yn2 = pitchacc;
yn3 = pitch;
xk++;
}

void serialEvent (Serial port)
{

  currentAngle = float(port.readStringUntil(gyro));
  pitchacc = float(port.readStringUntil(accel));
  pitch = float(port.readStringUntil('\n'));
}

GoToLoop

https://forum.Processing.org/two/discussion/8045/how-to-format-code-and-text
https://forum.Processing.org/two/discussions/tagged?Tag=bufferuntil()

dragal

        currentAngle += gyroRate * (tt - t) / 1000.0;
        Serial.print ( currentAngle);
        Serial.print ("\t\t");
      }
      pitchacc = atan2(accel.readY_G(), accel.readZ_G()) * 180 / 3.14;
      Serial.print (pitchacc);
      Serial.print ("\t\t");
      pitch = (pitchacc * 0.05 + 0.95 * currentAngle);
      Serial.println (pitch);

Here is my arduino code.

As I can guese I have something wrong with transforming data from string to float... in these 3 lines :

  currentAngle = float(port.readStringUntil(gyro));
  pitchacc = float(port.readStringUntil(accel));
  pitch = float(port.readStringUntil('\n'));

GoToLoop

Modify the Arduino's source to separate those sent values w/ '\t':

// Forum.Processing.org/two/discussion/14988/drawing-of-graphs-from-i2c-imu#Item_3
// GoToLoop (2015-Feb-18)

import processing.serial.Serial;
float[] vals = {};

void setup() {
  noLoop();
  new Serial(this, "COM5", 9600).bufferUntil(ENTER);
}

void draw() {
  println(vals);
}

void serialEvent(final Serial s) {
  vals = float(splitTokens(s.readString()));
  redraw();
}

dragal

If I understand correctly, I can print each value from String using " [ ] ", can't I? But when I try to execute " println (vals[0]); " e.x., it says " NullPointerException'. For example if I need to build up 3 graphs I need to have 3 variables but I cannot use them separately.

GoToLoop

For my example to work, you need to modify how the data is sent from the device.
For example, if you send 3 float values: println("10.5" + "\t" + "-2.3" + "\t" + "1.0");

In Processing's end, it's expected: vals[0] = 10.5, vals[1] = -2.3, vals[2] = 1.0

dragal

I am just really confused. I understand how splitTokens operates and the rest. I can send to processing all data, and if I use your sketch it gives me such numbers : (see picture "example") But if I for example want to print only one of them ( e.x. [0] or [1]) it says me "NullPointerException"... May be I didn't understand correctly how to modify arduino's code may be something else... Here my adruino's code

#include <l3g4200d.h>
#include <lis331dlh.h>
#include <lis3mdl.h>
#include <LPS331.h>
#include <troyka-imu.h>
#include <Wire.h>
Gyroscope gyro;
Accelerometer accel;
float rotationThreshold = 1;   //Минимальная угловая скорость, которую можно не учитывать
float pitchacc;
float currentAngle;
float pitch;
boolean DR;
unsigned long t;
unsigned long tt;
void setup() {
  Serial.begin (9600);
  gyro.begin();
  gyro.setRange(RANGE_500);
  accel.begin();
  DR = true;
  pitch = 0;
}
void loop() {
  // Тут только для первого лупа задаю начальное значие угла отклонения для гироскопа, который равен показанию акселерометра
  if (DR = true)
  {
    currentAngle = atan2(accel.readY_G(), accel.readZ_G()) * 180 / 3.14;
    t = micros();
    DR = false;
  }
  float gyroRate = gyro.readX_DegPerSec();
  tt = micros();
  //Игнорировать показания гироскопа, если они меньше заданного лимита
  if (gyroRate >= rotationThreshold || gyroRate <= -rotationThreshold) {
    currentAngle += gyroRate * (tt - t) / 1000.0;
  }
  Serial.print(currentAngle);
  Serial.print ("\t");
  pitchacc = atan2(accel.readY_G(), accel.readZ_G()) * 180 / 3.14;
  pitch = (pitchacc * 0.05 + 0.95 * currentAngle);
  Serial.print (pitchacc);
  Serial.print ("\t");
  Serial.println ( pitch);
  t = tt;
}

GoToLoop

Arduino code seems correct. Maybe show us how you're trying to get each individual value from vals[].

dragal

Refering to splitToken reference explnation on Processing website, I want to get all the value independently and use them as y - coordinate for graphs building.

GoToLoop

Until serialEvent() is finally called back for the 1st time, vals is still null!
An easy fix is simply instantiating some float[] array at the same time vals is declared:
Change: float[] vals; to float[] vals = new float[3];

dragal

Perfect! Now it is what I want! Appreciate it! One moment, could you please describe a bit how float [] vals = new float[3]; works? I have read on website, but still it is not absoulutelly clear for me. Thanks!

GoToLoop

• Processing always runs draw() at least once, even w/ noLoop() active.
• If we only declared variable vals, it's still null when it reaches println(vals[0]);.
• Logically vals[0] crashes b/c we can't do anything w/ null but print it raw: println(vals);
• However, by initializing vals w/ an arbitrary new float[3], it's not null anymore.
• And it's now safe for println(vals[0]);. Although it's just gonna display 0.0 at that 1st draw().
• But once serialEvent() gets triggered, vals is re-assigned w/ the correct float[] array generated by float(splitTokens(s.readString())); expression. :-bd
• And then redraw() requests draw() to run once, displaying the correct received data from now on.

GoToLoop

void draw() {
  println(vals[0], TAB, vals[1], TAB, vals[2]);
}