Distinguish Data On Serial Communication

[mastert335]

Hi Everyone!

I have a question concerning serial communication: I have a joystick connected to a PC which I would like to send the input to my Arduino UNO, up to now I can get all the joystick information to Serial, my question is how can distinguish data coming to the Arduino? For example, the joystick has 4 axes, how to send data via Serial and know which axis does the data belong to ?

Thanks!

[PaulRB]

2 options:

1. You would send data telling the Arduino which axis the data was for, such as

<X,123>

This says the X axis value is 123.

2. Send both/all axis data as one message where the position in the message tells the Arduino which axis is which, like

<xxx,yyy,zzz,www>

In this format, the Arduino knows the Z axis value is always the third value.

[jremington]

Serial Input Basics - updated

Updated Version Please note that this is a revised version of the advice in this earlier Thread which has become very long. As far as possible I have kept the code examples identical or simplifed them slightly. It should not be necessary to refer to the older Thread, but feel free to do so. Contents The following sections are in this Tutorial Introduction Serial data is slow by Arduino standards Example 1 - Receiving single characters Why code is organized into functions Exampl…

[mastert335]

I like the : <X, 123> approch better.

I was thinking of sending structs,but
small issue is i can ONLY send String and the implementation isn't quite as straight forward as i thought.

[cattledog]

@mastert335

small issue is i can ONLY send String

Can you please elaborate on this constraint?

[mastert335]

Yes!

I am using Qt and the serial communication function used to write on the serial, expect a QByteArray( QByteArray can be used to store both raw bytes (including '\0's) and traditional 8-bit '\0'-terminated strings ) so i can't really send a struct(only QByteArray or Strings)

[jremington]

Please post a link to Qt, "the serial communication function" and the QByteArray.

Expect serious problems using String objects on the Uno. There is always a way to avoid them.

[mastert335]

Here is the link : QIODevice Class | Qt Core 5.15.12

https://doc.qt.io/qt-5/qbytearray.html

[cattledog]

@mastert335

I was thinking of sending structs

Because of possible packing issues I would avoid the struct and just send the QByteArray character arrays "<X,123>".

I don't think the efficiency of the binary transmission of the struct outweighs the complexity of implementing it.

From what I can tell, String Objects are not needed on the Arduino side.

[PaulRB]

@mastert335

I like the : <X, 123> approch better.

Why?

[david_2018]

@jremington

Expect serious problems using String objects on the Uno. There is always a way to avoid them.

The fact that a String object was used when sending the data in no way requires the use of String on the receiving device.

[mastert335]

Seems easier and more straight forward to implement, i will try both approches tonight and see which one is more convenient.

[mastert335]

That part of my problem, i don't know where to start to implement this on the UNO side.

I guess on the Qt side i can create a function doing the "<X,123>" and changing X and 123 depending on what axis and variable change.

[cattledog]

@mastert335

i don't know where to start to implement this on the UNO side.

With the Serial Input Basics tutorial linked in reply #2.

[mastert335]

Okay! I will have a look. One last thing : is it normal that i can't use the Serial Monitor while i am receiving data ? Is there a way to counter this ?

[PaulRB]

You need to sync the arduino with the incoming messages. That's why I suggested the "<" and ">" - they can be used for that purpose. Otherwise, the Arduino could start receiving part way through a message and it wouldn't make sense.

So your arduino code would wait for a "<", then the next character would be the axis/joystick channel. Then there would be the comma (you could forget the comma if the channel will always be a single character. Then you can use Serial.parseInt() to read the value. Finally there would be the ">" markling the end of the message which you can discard.

[cattledog]

@mastert335

One last thing : is it normal that i can't use the Serial Monitor while i am receiving data ? Is there a way to counter this ?

If you have your PC program using QT connected to the usb serial port of the Arduino Uno and its onboard usb>ttl converter, you can not connect the monitor to that same port.

You should be able to connect a second USB serial device using a separate usb to ttl converter connected to pins with a software serial instance.

[mastert335]

Thanks everyone, i was able to get everything to work correctly!