Java+Arduino Communication

Projects Interfacing w/ Software on the Computer
1

Hi everyone, maybe someone wrote another topic similar like this, but I didn't find.

The problem is that I'm trying to create a really communication between Arduino and Java through message passing, I mean, if I send with Java an string message, I would like to Arduino read the string and depend of the value, return the correct value. For example, if Java send "REQ" Arduino should return "Yes"; if Java send "VAL", Arduino should return "100", etc.
The problem is: If i realize experiment with Arduino serial monitor, this works perfectly, but if I did with java, doesn't work (for example If i send "REQ" and I would like to obtain String+"OK" from the board, Arduino return ROKEOKQOK,instead of REQOK.

My javacode for write and read to/from serial port is:
----READ---
public String read(){
String value="";
try {
while(inputStream.available()>0)
value+=(char)inputStream.read();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return value;
}
--write---
public boolean write(String text){
try{
outputStream.write(text.getBytes());
}catch(IOException e){
return false;
}
return true;
}

And the Arduino code:

boolean entrado=false;
String cadena="";
void setup()
{
Serial.begin(9600);

}

void loop() {
while(Serial.available()>0){
cadena += (char)(Serial.read());
entrado=true;
}
if(entrado){
cadena+="OK";
Serial.print(cadena);
cadena="";
entrado=false;
}
}

If anyone had the same problem and could help me, I would be grateful.

Thanks!!

2

Serial data transmission is relatively slow. You can read it much faster than it can be sent. Somehow, you need to tell the Arduino when a packet is complete. Send something like "REQ;" or "VAL:".

Then, on the Arduino, read, but don't print or append OK, all serial data until the end of packet marker ( ; ) is received.

And, yes, this is a very common question.

3

mmm..ok..I get it..but now, I have to send two data packets to receive one "answer-data", I mean if I send port.write("REQ"); port.write("REQ"); I receive just one "REQ;OK" and if I send just one port.write("REQ") I don't receive any answer. I think I'm forgetting something....any idea? :slight_smile: :slight_smile:

4

I think I'm forgetting something....any idea?

Sure. You forgot to post your modified code.

5

haha, sorry :P

---code to sent messages---
String mensaje="REQ;";
boolean entrado=false;
do{
port.write(mensaje);
System.out.println("Sent");
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
if(!port.getLastValue().equals("")){
System.out.println(port.getLastValue());
entrado=true;
}
}while(!entrado);

----receive messages code--
public synchronized void serialEvent(SerialPortEvent oEvent) {
byte[] buffer = new byte[20];
if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
try {
int numbytes=0;
while(inputStream.available()>0){
numbytes = inputStream.read(buffer);
}
lastValue = new String(buffer,"ASCII");
} catch (Exception e) {
System.err.println(e.toString());
}
}
}

---write code---
public synchronized boolean write(String text){
try{
outputStream.write(text.getBytes());
}catch(IOException e){
return false;
}
return true;
}

----arduino code----
boolean entrado=false;
char inChar;
String cadena="";
void setup()
{
Serial.begin(115200);
}

void loop() {
while(Serial.available()>0){
inChar = (char)Serial.read();
cadena+=inChar;
if(inChar==';')
entrado=true;
}
if(entrado){
cadena+="OK";
Serial.print(cadena);
entrado=false;
cadena="";
}
}

Thanks!!! =)

6

I'm not a Java expert, but I'm wondering why you put the thread to sleep after sending the message. Does the receipt of serial data wake the thread? Does serial data get received while the thread is sleeping?

When happens if you send the message, then enter the do/while loop that waits for a reply, without sleeping?

7

I did all that I saw in another examples. if I remove thread sleep doesn't work,

port.write(mensaje);
do{
System.out.println("Sent");
if(!port.getLastValue().equals("")){
System.out.println(port.getLastValue());
entrado=true;
}
}while(!entrado);

still waiting forever :S