RS232 and how to build some datas into a waveform

[Mike.Ad]

Hello everyone !

I would like to ask you a question about how to build some datas into waveform.

Let's me explain :

Actually, I am working on a project with a PIC.

The PIC sent 3 informations to Laview by RS 232 :'velocity;current;tension\n'

Lynn and Crossrulz help me to make a diagram that allows to read datas and displays them with charts.

It works perfectly.

Now, I would like to display some datas from a sensor (dynamic datas)  and double datas from RS232 on the same chart with different plot.

So, I have to build double datas into waveform,  convert double datas into dynamic datas.

I have tried something : I used 'Convert to dynamic data' function but it doesn't work and I don't know why.

Can you help me ?

I join you :

- VI

- a gif that shows what's happening

- screenshot

Notice : I used 'simulate signal' to represent a sensor

Thanks for your help

[crossrulz]

First of all, lets avoid the Dynamic Data Type like its the plague.  It is asking for nothing but trouble.

Secondly, look in the Waveform palette.  There is a Build Waveform in there.  A Waveform is nothing but an array of data (Y), a sample rate (dt), and the start time (T0).  If you can supply those, then you can quickly make a waveform.  The chart will take an array of waveforms.

[Mike.Ad]

Hello Crossrulz !

Thanks again for your help.

I have found Build Waveform but I get a strange result.

As first step, I have simplified my problem and I have just tried to build a waveform from my datas.

Since Build Waveform must have an array as input, I have used  Array Subset.

As result, I don't get a plot but if you pay attention, you can see a little white dot around my value.

How can I fix that ?

Thanks again

[GerdW]

Hi Mike,

Since Build Waveform must have an array as input, I have used  Array Subset.

And what's the reason for that decision? And what's the reason to use a subset of just one element? Why not use the whole array for your waveform?

How many elements do you have in that array?

Your serial port is set to use a TermChar. Does your device use a TermChar? When it does: do you have a TermChar after each sample?

[Mike.Ad]

Hi GerdW !

Thanks for your reply

               And what's the reason for that decision? And what's the reason to use a subset of just one element? Why not use the whole array for your waveform?

Well, I sent 3 datas (velocity, current, tension). With RS232, we have to consider strings separated by semicolons.
So it is : 'velocity;current;tension'.
With Labview, I converted string into an array then, I used Index Array to get scalars (a scalar for velocity, for the current and the tension) and used a chart to get a plot.

Now, I would like to use waveforme chart.
Build Waveforms must have an array as a input and not a scalar. So, I deleted the Index Array and add ArraySubset.
Of course, there is only one element (equivalent to a scalar). But I can wire with that solution. I don't know if there is a better way to solve my problem (I am a beginner in LabView)

I can't use the whole array in the same time because it contains values from different measures (velocity, current and tension)

             How many elements do you have in that array?

3 elements : velocity, current and tension.
Their values evolves in time

What do you mean by TermChar ? 
When I send some datas and create an indicator, I can read some values. It is just when I try to build a waveform, it doesn't work.

Thanks for your help

[crossrulz]

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Mike.Ad wrote:

What do you mean by TermChar ?

---

A termination character is a character that flags that the message has completed.  An End Of Line is typically the termination character.

I think your problem could be that you are not supplying a timestamp to your waveforms.  Use the Current Time to set the T0 for your waveforms.

[Mike.Ad]

Alright, I have used the current time to set the T0 for my waveforms.

Now, I get a proper plot ! Thanks.

However, there is still a problem : The Time scale change. 

It is very weird because the minimal value is now 3.4*10^9 instead of 0.

How can I fix that ?

Thanks again

[GerdW]

Hi Mike,

change the X axis formatting to "absolute time"…

[Mike.Ad]

Hi GerdW !

You are right !

With "absolute time", the x axis is stable.

Thanks !

However, I would like to keep my old format.

In the beginning, the X axis fomat was 'Float'. 

What can I do to keep this format and get a proper X axis ?

Thanks

[crossrulz]

You could read the time right before going into the loop and then subtract the current time from that and use that result as your T0.