Using the Serial Plotter (Solved)

Projects Programming
1

I am trying to learn how to use the Serial Plotter and used the following sketch:

int i=0;
float ySin;
float yCos;

void setup() {
Serial.begin(9600);
Serial.print("Sin:0, ");
Serial.print("Cos:0, ");
delay(200);
}

void loop() {
ySin=220*sin((PI/180.0)*i);
yCos=220*cos((PI/180.0)*i);
Serial.print(ySin);
Serial.print(" ");
Serial.println(yCos);
delay(1);
i++;
}

This gave the following output:

Screenshot 2025-09-16 at 11.00.36
Screenshot 2025-09-16 at 11.00.361602×1000 75.3 KB

I wanted to show Sin & Cos instead of value 1 & value 2 and after a bit of investigation changed the sketch to the following:

int i=0;
float ySin;
float yCos;

void setup() {
Serial.begin(9600);
delay(200);
}

void loop() {
Serial.print("Sin:0, ");
Serial.print("Cos:0, ");
ySin=220*sin((PI/180.0)*i);
yCos=220*cos((PI/180.0)*i);
Serial.print(ySin);
Serial.print(" ");
Serial.println(yCos);
delay(1);
i++;

}

This was the output:

Screenshot 2025-09-16 at 10.58.59
Screenshot 2025-09-16 at 10.58.591600×1008 56.4 KB

Labels are fine but plot is just a flatline!

Any pointers on my mistakes would be much appreciated.

Also would it be possible to stop the Y axis from moving?

One more question: is it possible to show a whole sin wave/cosine wave in the window?

2

Hi @SierraGolfMike. The data format understood by the plotter has the following format:

<label>:value<delimiter><label>:value

You are producing data with the following format:

Sin:0, Cos:0, 42 123

The plotter is not able to parse this data.

The equivalent to your first sketch, but with labels would be:

  ySin = 220 * sin((PI / 180.0) * i);
  yCos = 220 * cos((PI / 180.0) * i);
  Serial.print("Sin:");
  Serial.print(ySin);
  Serial.print(" ");
  Serial.print("Cos:");
  Serial.println(yCos);

You can prevent the auto-scaling by adding additional variables with constant values set to the Y axis scale you want:

int i = 0;
float ySin;
float yCos;

void setup() {
  Serial.begin(9600);
  delay(200);
}

void loop() {
  Serial.print("_:-250 __:250 "); // Prevent change to Y axis scale by plotter's auto-scaling feature.
  ySin = 220 * sin((PI / 180.0) * i);
  yCos = 220 * cos((PI / 180.0) * i);
  Serial.print("Sin:");
  Serial.print(ySin);
  Serial.print(" ");
  Serial.print("Cos:");
  Serial.println(yCos);
  delay(1);
  i++;
}

The Arduino IDE developers are tracking the request for a built-in option to disable auto-scaling here:

:red_exclamation_mark: Please only comment on the GitHub issue thread if you have new technical information that will assist with the resolution. General discussion and support requests are always welcome here on Arduino Forum.

There is no easy way to configure the number of data points visible in the plotter:

You could adjust your code so that the wave is represented by only 50 data points.

3

Many thanks for your reply, I have taken your advice and my altered code as shown below. However it only shows the Sin value and plot! I can’t see anything I have missed. I will look at your other points once I get this bit working. I am using IDE 2.0.0 if that makes any difference.

int i=0;
float ySin;
float yCos;

void setup() {
Serial.begin(9600);
delay(200);
}

void loop() {
ySin=220*sin((PI/180.0)*i);
yCos=220*cos((PI/180.0)*i);
Serial.print("Sin:");
Serial.print(ySin);
Serial.print(" ");
Serial.print("Cos:");
Serial.println(yCos);
delay(1);
i++;

}

See below:

Screenshot 2025-09-16 at 12.09.02
Screenshot 2025-09-16 at 12.09.021592×994 60.1 KB

4

That sounds like a good option, I will give it a go once I get my main issue sorted. Thank you

5

I'm not able to reproduce the fault. The sketch you provided works as expected for me:

image
image666×597 20.2 KB

I was able to infer that fact from your screenshots. However, it is indeed relevant in regards to your question:

Arduino IDE 1.x Serial Plotter shows 500 data points as compared to Arduino IDE 2.x's 50, so would be better suited to displaying the full wave.

6

@UKHeliBob found this recently

this seems way more capable than the built in plotter.

As a side note, I don't understand who as an engineer could make such a limiting decision... It seems so useless...

7

I tried using this sketch and the result is a flatline with no labels! What IDE version are you using, there would appear to be an anomaly with 2.0.0

Screenshot 2025-09-16 at 12.44.18
Screenshot 2025-09-16 at 12.44.181608×1002 64 KB

8

It works as expected for me:

image
image795×502 20.2 KB

2.3.6

Are you really using version 2.0.0, or are you using that as an inaccurate shorthand to refer to the the Arduino IDE 2.x version series in general. I ask because the Arduino IDE 2.0.0 release is seriously outdated and many improvements and bug fixes have been made to the IDE since that release.

9

The serial plotter's window with your code in IDE 1.8.19

image
image3798×2110 391 KB

(I only changed the Serial baud rate to 115200 because 9600 is so old school).

1 Like
10

There is a way of changing the IDE 2.x.x Serial plotter to display 500 points like the IDE version 1.x.x does.
(That would make it look like J-M-L's plot in post #9.)

Details are shown how to do it at: https://forum.arduino.cc/t/serial-plotter-output-too-fast/1233965/9.

I don't claim to be the originator of this information, the original work is by Alex-Tsyganok.

11

Yes was using IDE 2.0.0, however I have just tried the sketch on a laptop with IDE 2.3.5 and it works as you described. Many thanks for your help.

12

That output looks much better, hopefully the developers will address the issue in a future update.

13

You are welcome. I'm glad it is working with 2.3.5!

Is there a specific reason why you are using 2.0.0? I know that some users are not able to update all the way to the latest version due to a loss of compatibility with some obsolete operating systems, but I'm not aware of any such limitation that would force using 2.0.0 specifically.

14

Here's the IDE 2.3.6 Serial Monitor modified to show 500 points, as mentioned in post #10:

IDE 2.3.6 Serial Plotter - 500 points
IDE 2.3.6 Serial Plotter - 500 points1359×719 108 KB

You could even adjust it to plot 360 points if you wanted to display exactly one full cycle.

15

I believe the reason the sketch did not work with Arduino IDE 2.0.0 was because the developer of Serial Plotter did not provide compliance with all ssupported delimiters](Arduino/build/shared/ArduinoSerialPlotterProtocol.md at master · arduino/Arduino · GitHub) when using labeled data sets. At the time of 2.0.0, the only delimiter supported under these conditions was the comma.

So you could probably make it work with 2.0.0 using this sketch:

int i = 0;
float ySin;
float yCos;

void setup() {
  Serial.begin(9600);
  delay(200);
}

void loop() {
  Serial.print("_:-250 __:250 "); // Prevent change to Y axis scale by plotter's auto-scaling feature.
  ySin = 220 * sin((PI / 180.0) * i);
  yCos = 220 * cos((PI / 180.0) * i);
  Serial.print("Sin:");
  Serial.print(ySin);
  Serial.print(",");
  Serial.print("Cos:");
  Serial.println(yCos);
  delay(1);
  i++;
}

(note the Serial.print(",");)

Compliance with the Arduino Serial Plotter protocol specification was introduced later:

and that version of Serial Plotter was used starting with Arduino IDE 2.0.1:

16

I agree with you there!

17

I updated to IDE 2.3.6 before seeing this post and it is working fine now. Thanks

18

That’s exactly what I was thinking, struggling to find the file on my Mac though. Thanks for your input.

19

Followed the instructions and it works a treat. Many thanks!

1 Like
20

Glad you managed to find it.

I keep a copy of the instructions in a handy place.
Some IDE updates make it revert back to 50 points, and you have to repeat the process.