New Arduino Serial Plotter

With the release of Arduino IDE v1.6.6, a new tool was given to the users called the Serial Plotter. The idea of it is to be able to visualize the data you return, beyond just seeing numbers spit out onto the serial monitor. I’m a big fan of anything that lets people conceptualize the data their receiving in intuitive ways, so having a convenient graph generator in your IDE should be great.

What The Arduino Serial Plotter Is

The Arduino Serial Plotter is, as the name suggests, a software utility within the IDE that takes incoming serial values over the USB connection. Instead of just displaying the raw values to a TTY monitor, it graphs them against an X/Y axis. The vertical Y axis auto adjusts as the value of your output increases or decreases, and the X axis is a fixed 500 point axis with each tick of the axis equal to an executed serial println command.

The plotter updates each time the serial line pops with a new value, which is to say, it updates slowly. Well, slow from a microprocessor standpoint.

Testing the Serial Plotter

We’ll start off by copying the example sketch that was displayed in the promo graphic for the release of v1.6.6.

#include "math.h"       // This will allow us to run the "sin" function.

void setup() {

  // Enable Serial Output
  Serial.begin(9600);
  while (!Serial);

}

void loop() {

  // Describe the upward swing of the sine wave
  for (double i = -1.0; i <= 1.0; i = i + 0.1) {
    Serial.println (sin(i));
    delay(10);
  }

  // Describe the downward swing of the sine wave
  for (double i = 1.0; i >= -1.0; i = i - 0.1) {
    Serial.println (sin(i));
    delay(10);
  }
  
}

#include "math.h" // This will allow us to run the "sin" function.

void setup() {

// Enable Serial Output

Serial.begin(9600);

while (!Serial);

}

void loop() {

// Describe the upward swing of the sine wave

for (double i = -1.0; i <= 1.0; i = i + 0.1) {

Serial.println (sin(i));

delay(10);

}

// Describe the downward swing of the sine wave

for (double i = 1.0; i >= -1.0; i = i - 0.1) {

Serial.println (sin(i));

delay(10);

}

Upload that sketch using v1.6.6 and then open the serial plotter by either clicking on Tools / Serial Plotter or pressing CTRL+SHIFT+L (on windows).

After the plotter opens up, you’ll see the sine wave begin to be drawn between -1.0 and 1.0 and back again. The function used in the sketch describes 20 values on the way up to to 0.84 and 20 values on the way back down to -0.84… 40 points to be plotted per duty cycle.

As soon as the plot hits the right edge of the window, it starts scrolling from right to left, and this is the first problem I have with it… there’s no way to stop it. There’s no “uncheck autoscroll” to buffer the values outside the display like there is in the serial monitor. If Serial.println(); keeps hammering away, your data scrolls off the left side of the graph without you able to do a thing about it.

Serial Plotter X Axis

The X axis is a fixed axis with each value representing one output of the Serial.println(); function. There is no time scale to speak of, really.

Ok, there is a time scale I suppose, if you use the baud rate of the serial monitor that you’ve set, but measuring time by how many serial outputs you received is a pretty crude way to measure anything

Along with that limitation, is the fact that the displayed axis is fixed at 500 points. It doesn’t matter how large or small you make your window, it’s still 500 points. Period. Sort of like a shift registers, when data point 501 shows up, data point 1 is lost. And since there’s no way to stop the plot from scrolling, you’ll need to compensate for this in your code.

To show what I mean, this sketch will generate a square wave from 100 to 50 to 100 to 50, and do it 5 times. Note that all the work happens in Setup as a crude way of ensuring it only executes once.

void setup() {

  Serial.begin(9600);
  while (!Serial);

  
  for (int i = 0; i < 100; i++) {
    Serial.println (100);             // Data Points   0 -  99
  }

  for (int i = 0; i < 100; i++) {
    Serial.println (50);              // Data Points 100 - 199
  }

  for (int i = 0; i < 100; i++) {
    Serial.println (100);             // Data Points 200 - 299
  }

  for (int i = 0; i < 100; i++) {
    Serial.println (50);              // Data Points 300 - 399
  } 

  for (int i = 0; i < 100; i++) {
    Serial.println (100);             // Data Points 400 - 499
  }
  
}

void loop() {

}

void setup() {

Serial.begin(9600);

while (!Serial);