topic Re: Simultaneous actions in the User Interface in LabVIEW

Simultaneous actions in the User Interface

mirelche — Mon, 09 Mar 2020 07:46:59 GMT

Hi!

I am new to LabView, so I am hoping, that I can find some help here!

I have developped a User Interface. While testing it, I noticed a bug, namely:

while the command prompt is logging or a countdown is still in progress, I cannot seem to press any button, which might bring my system in a state which is not safe.

I am using sequential structure and events. I read about the problem and apparently one option is to deselect the lock front panel option from the event properties, however I am not sure if this is a good idea. I also looked into asynchronous processing of the VIs, but it also did not work. Does someone have an idea how it can be done?

Thanks, Mirela

Re: Simultaneous actions in the User Interface

GerdW — Mon, 09 Mar 2020 08:25:59 GMT

Hi mirelche,

@mirelche wrote:

while the command prompt is logging or a countdown is still in progress, I cannot seem to press any button, which might bring my system in a state which is not safe.

I am using sequential structure and events.

Using sequences might be the problem. (Usually you don't need sequences at all when you THINK DATAFLOW!)

Using event structures together with sequences most often also leads to problems.

So my conclusion is: it's your programming style which is responsible for the problems you see.

For more detailed analysis you need to attach your VI(s)…

Re: Simultaneous actions in the User Interface

mirelche — Mon, 09 Mar 2020 08:48:30 GMT

Hi, GerdW!

Thank you for the quick response! I am very new to LabView, so it is possible that it is my programming as well, so I did this small VI which takes a countdown and has a stop button. Here, I have the same problem that I cannot press the stop button at all while the countdown is in progress. I am attaching it and I hope that I can find some help.

Thanks!

Re: Simultaneous actions in the User Interface

PazhanivelVenkatt — Mon, 09 Mar 2020 09:01:02 GMT

I am still using LV 2017, not able to view your code.

Will be helpful if you can down convert and share.

Since you mentioned you are new to LabVIEW please do go through LabVIEW Design Patterns (Master Slave/Producer Consumer) which will solve your problem of continuous acquisition as well respond to user actions.

Re: Simultaneous actions in the User Interface

GerdW — Mon, 09 Mar 2020 09:08:31 GMT

Hi Mirela,

for me the same applies: please downconvert your VI to LV2017 (Edit -> save for previous). Then attach the downconverted VI again…

Re: Simultaneous actions in the User Interface

mirelche — Mon, 09 Mar 2020 09:14:14 GMT

Hi, everyone!

Here I am attaching my code in Labview 2017.

Best regards

Re: Simultaneous actions in the User Interface

GerdW — Mon, 09 Mar 2020 09:21:19 GMT

Hi Mirela,

did you read the LabVIEW help on the event structure? Did you read the "Caveats" when using the event structure?

General rule: an event case should be executed as fast as possible.

Your "OK button" event starts a countdown loop executing NOT "as fast as possible", but instead blocking the outer while loop. As long as the outer while loop is blocked you cannot handle any other events!

Place the countdown code inside the Timeout event (without that inner while loop) or use a parallel running loop so your event handler loop will not be blocked!

Generic advice:

Buttons should be placed inside their event case so they will be "visually processed" - this is important for latching buttons!
No need for a "boolean" local variable when the "boolean" terminal is unused!
This "IF x<0 THEN 0 ELSE x" can be replaced by the MinMax function with zero…

Re: Simultaneous actions in the User Interface

mirelche — Mon, 09 Mar 2020 09:35:55 GMT

Hi,

thank you for the quick response! However, i do not want to place my countdown loop in the timeout, as i want it to be executed only when I press the start button. Can you be more specific about the parallel running loop? Where should i place it?

Thanks!

Re: Simultaneous actions in the User Interface

GerdW — Mon, 09 Mar 2020 09:47:22 GMT

Hi Mirela,

@mirelche wrote:

However, i do not want to place my countdown loop in the timeout, as i want it to be executed only when I press the start button. Can you be more specific about the parallel running loop? Where should i place it?

This is a silly explanation for not wanting to use the TimeOut event. See attachment…

Re: Simultaneous actions in the User Interface

wiebe@CARYA — Mon, 09 Mar 2020 10:05:54 GMT

@GerdW wrote:

Generic advice:

Buttons should be placed inside their event case so they will be "visually processed" - this is important for latching buttons!

No need for a "boolean" local variable when the "boolean" terminal is unused!

This "IF x<0 THEN 0 ELSE x" can be replaced by the MinMax function with zero…

And do the future-you a favor, and learn to straighten those wires.

This might be a bit annoying right now, but once you developed a bad habit, it will be near impossible to correct.

Bugs hide in messy code...

Re: Simultaneous actions in the User Interface

mirelche — Mon, 09 Mar 2020 10:23:18 GMT

Hi!

Thank you! i understand it much better now!

Have a nice day!

Re: Simultaneous actions in the User Interface

mirelche — Mon, 09 Mar 2020 12:39:44 GMT

Hi!

I just have another question for you. As you said, I should not use event with sequential structure, I am now trying to rebuild my code with using shift registers and events. However, I have quite many buttons and indicators.

Do you suggest me to create a shift register for each one and then in the timeout create several case structures as you did to show what happens?

The problem is that all of these buttons execute respective actions in a strict sequence, hence this is why i wanted to use the sequence structure.

Best regards

Mirela

Re: Simultaneous actions in the User Interface

GerdW — Mon, 09 Mar 2020 13:08:51 GMT

Hi Mirela,

@mirelche wrote:

The problem is that all of these buttons execute respective actions in a strict sequence, hence this is why i wanted to use the sequence structure.

When you want to execute certain actions in a defined order you should think of a statemachine…

Re: Simultaneous actions in the User Interface

wiebe@CARYA — Mon, 09 Mar 2020 15:20:05 GMT

@mirelche wrote:

I just have another question for you. As you said, I should not use event with sequential structure,

You shouldn't (need to) use a sequence structure at all.

Ideally, sequence is either irrelevant (so why force it), or forced by dataflow. There are hardly situations where order is relevant, and there's no dataflow. If this happens, a flat sequence structure (never a stacked one) can seem convenient at first, but not in the long run. And they're always avoidable, with a tiny bit of work.

Re: Simultaneous actions in the User Interface

billko — Mon, 09 Mar 2020 17:23:54 GMT

wiebe@CARYA wrote:

@mirelche wrote:

I just have another question for you. As you said, I should not use event with sequential structure,

You shouldn't (need to) use a sequence structure at all.

Ideally, sequence is either irrelevant (so why force it), or forced by dataflow. There are hardly situations where order is relevant, and there's no dataflow. If this happens, a flat sequence structure (never a stacked one) can seem convenient at first, but not in the long run. And they're always avoidable, with a tiny bit of work.

I think a sequence structure is "allowable" in this one situation: Where you are reading from or writing to a variable and you need to make sure that the read or write happens exactly when it is supposed to. Even then, technically you could make a subVI to do this, but I will allow sequence structure laziness to avoid the creation of a subVI just for that one purpose.

Re: Simultaneous actions in the User Interface

mirelche — Mon, 09 Mar 2020 17:49:32 GMT

Hi,

this is actually what i need to do. My Vi has many tabs and in each tab there are buttons. These buttons actuate usually a series of actions, eg start sensor logging, or wait 10 second with a countdown and then send signal to a LED.

Initially, I had sequences and events with the buttons inside, and it was functional, except for the problem which i had that while a countdown is running, then i cannot actuate the stop button, for instance.

So what would you recommend me? I am a bit confused, now what i have done is just started using shift register and events and cases instead of sequences, but I think there it is much harder to represent for instance a series of 10 things which need to happen in a certain order after a button is pressed.

Re: Simultaneous actions in the User Interface

GerdW — Mon, 09 Mar 2020 19:20:49 GMT

Hi Mirela,

@mirelche wrote:

My Vi has many tabs and in each tab there are buttons. These buttons actuate usually a series of actions, eg start sensor logging, or wait 10 second with a countdown and then send signal to a LED.

Tabs are irrelevant from the block diagram point of view: all you need are the terminals and events for your UI elements.

I think there already was a suggestion to implement a producer-consumer scheme. The event handler loop would be the producer, while one or more consumers would execute your "series of actions"…