Passing a variable from Ardunio to Processing

in Integration and Hardware • 9 months ago

Hi,

I am trying to pass a variable called elapsedTime (line 20.) from an Ardunio sketch to a Processing sketch. I know in the Processing I can't read into a float like this. A float is 4 bytes and a read reads one byte. (line 3 of the Processing sketch)

The Ardunio code is as follows,

int ledTX = 12; //Receives InfraRed signal
int photodiodePin = 2; // Photodiode connected to digital pin 2
int lastState;
unsigned long startTime;
unsigned long elapsedTime;
void setup() {
Serial.begin(9600);
pinMode(ledTX, OUTPUT);
pinMode(photodiodePin, INPUT); // sets the digital pin as input to read photodiode
}
void loop() {
byte currentState = digitalRead(photodiodePin);
digitalWrite(ledTX, HIGH); // turn the TX Infrared LED on
if(currentState == LOW && lastState == HIGH){
startTime = millis();
}
if(currentState == HIGH && lastState == LOW){
elapsedTime = millis() - startTime;
Serial.println(elapsedTime);
Serial.write(elapsedTime);
}
lastState = currentState;
}

The Processing code is as follows,

import processing.serial.*;
Serial port;
float elapsedTime;
void setup() {
size(200, 200);
background(204);
noStroke();
port = new Serial(this, 9600);
}
void draw() {
if (0 < port.available()) {
elapsedTime = port.read();
}
println(elapsedTime);
}

I was getting help with this here in the Arduino forum, but am stuck now.

Any help would be greatly appreciated.

Thanks,

Shane

Replies(8)

benja

Re: Passing a variable from Ardunio to Processing

9 months ago

Hi,

i don't see why you need float, since elapsedTime seems to be an integer. But it doesn't really matter, the principle is the same. There was a similar question a few days ago, maybe this helps:
https://forum.processing.org/topic/sending-data-from-arduino-to-processing-serially#25080000001734449

Let me know, if you need further help.

ofeyrpf

Re: Passing a variable from Ardunio to Processing

8 months ago

Hi,

I haven't been able to get working on this in a while. But I am trying to get it going again now.

Is there any way to divide up a number into bytes, send each byte one at a time and reassemble them again in the Processing sketch?

I use 'Processing a programming handbook for visual designers and artists' by Casey Reas and Ben Fry. But all the examples of serial communication either have values up to 255 or map values to a range of 0 to 255. This latter option I can't do because I don't have an upper limit for the time interval I am trying to send.

Thanks,

Shane

ofeyrpf

Re: Passing a variable from Ardunio to Processing

8 months ago

I understand that the whole point of serial communication is to send 1 byte at a time. So does that mean I can only send a number between 0 and 255? In this case i am sending milli seconds, so how do I send a time greater than a quarter of a second?

Thanks,

Shane

benja

Re: Passing a variable from Ardunio to Processing

8 months ago

You can send strings as well. In arduino, you use Serial.write() for bytes and Serial.print() or Serial.println() for strings.
Have a look into the thread i linked above, there i posted an example. If you have problems to integrate it into your code, please show what you tried, then one could try to find out what went wrong.

ofeyrpf

Re: Passing a variable from Ardunio to Processing

8 months ago

Hi,

I am trying to implement your code into mine. Here's my attempt.

Ardunio:

int ledTX = 12; //Receives InfraRed signal
int photodiodePin = 2; // Photodiode connected to digital pin 2
int lastState;
unsigned long startTime;
unsigned long elapsedTime;
void setup() {
Serial.begin(9600);
pinMode(ledTX, OUTPUT);
pinMode(photodiodePin, INPUT); // sets the digital pin as input to read photodiode
}
void loop() {
byte currentState = digitalRead(photodiodePin);
digitalWrite(ledTX, HIGH); // turn the TX Infrared LED on
if(currentState == LOW && lastState == HIGH){ //rising edge
startTime = millis();
}
if(currentState == HIGH && lastState == LOW){ //sinking edge
elapsedTime = millis() - startTime;
Serial.println(elapsedTime);
}
lastState = currentState;
}

Processing:

import processing.serial.*;
Serial port;
int elapsedTime;
float value;
void setup() {
size(200, 200);
background(204);
noStroke();
port = new Serial(this, Serial.list()[0], 9600);
}
void draw() {
/*if (0 < port.available()) {
elapsedTime = port.read();
}*/
//println(elapsedTime);
}
void serialEvent(Serial p) {
// get message till line break (ASCII > 13)
String message = port.readStringUntil(13);
if(message != null){
value = float(message);
println(value);
}
}

I can see the Arduino sketch is working and I am getting what seem to be correct value in the serial monitor.

In the Arduino sketch what does the 5 in Serial.println(elapsedTime, 5); mean? When I put it in the values of time from the photogate are too large to be correct.

There seems to be a problem with the Processing sketch line 9,

port = new Serial(this, Serial.list()[0], 9600);

Is giving an error,

Error inside Serial.<init>0

Thanks,

Shane

Fritzing of circuit Photogate.fzz

ofeyrpf

Re: Passing a variable from Ardunio to Processing

8 months ago

Hi,

I understand from the Ardunio reference page, the formats in println(elapsedTime, formats).

I now use println(elapsedTime, DEC);

Seems ok but is this why I am getting the error in the Processing sketch?

Thanks,

Shane

ofeyrpf

Re: Passing a variable from Ardunio to Processing

8 months ago

I ran your sketch and see now that i can't have the serial monitor from the Arduino IDE open at the same time. that is why I was getting the error. It is all working now, I am very happy

The Processing sketch is now,

import processing.serial.*;
Serial port;
int elapsedTime;
float value;
void setup() {
PFont font;
font = loadFont("Stencil-48.vlw");
textFont(font);
textSize(98);
size(350, 130);
background(204);
noStroke();
port = new Serial(this, Serial.list()[0], 9600);
}
void draw() {
background(#2C90DB);
fill(0);
text(value/1000, 0, 100);
}
void serialEvent(Serial p) { //get message till line break (ASCII > 13)
String message = port.readStringUntil(13);
if(message != null){
value = float(message);
println(value);
}
}

Thanks,

Shane

benja

Re: Passing a variable from Ardunio to Processing

8 months ago

Hey,

if you pass a second parameter to print() it defines the number of digits for float-values.
If you pass an integer, you don't need a second parameter.

The error you described might come from selecting a wrong serial port.

println(Serial.list())

This will print a list of your available serial-ports, which one to choose depends on your operating system.
maybe it's 'Serial.list()[1]' for you, but i can't tell.

Edit:
Yes, the serial-monitor... always forget about that.
Glad to hear it works!

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