Value Signalling Event Case

Hi Guys,
I am trying to trigger an event using "Value Signalling" and i hit a little bit of snag.
I am reading logic inputs continuously and i wanted to trigger an event if there is a change on logic signals.
What i did is i read the logic signals initially so to get the default state and re-read again the logic signals inside the timed loop in the event case waiting for the signals to change.
However, the event keep triggering even there is no change in signal.
Any advice?
Regards
Ray
Solved!
Go to Solution.
Attachments:
untitled.PNG ‏85 KB

Of course you did not show any actual code (just an image) so we can only guess the overall program architecture and what's in the other cases and events.
Still, you might be over-thinking all this. Since the loop is already spinning it seems overkill to trigger things using signaling events. All you probably need is a small case structure that executes additional code whenever things change. Events are primarily used to handle user interaction from the front panel. You just need to branch depending on the "changed/not_changed" case, which is trivial.
LabVIEW Champion . Do more with less code and in less time .

Similar Messages

How i use value signaling Event?

how i use Value signaling event by labview?
can you send me example?

Wiring a value to Value(signaling) is like having a user click a button. Here is an example.
- tbob
Inventor of the WORM Global
Attachments:
Trigger_Other_Event[2].vi ‏156 KB

Very strange behaviour of table values and event case

Hi all
i'm becoming crazy on my .vi
i want to change the second col values on click from yes to no and from no to yes simply by a click.
The problem is that this changing happens after some clicks on an old position.
Try to click on some "no" on the file that is attached.
Thanks a lot!
Dario
http://www.sd-studio.it - web design agency
Attachments:
Ecu_wizard.vi ‏101 KB

The issue took me a sec to understand but here it is. You are trying to change the value during the mouse up event. And you do... however you have just selected that cell in the table. So LabVIEW is waiting for the user to change the value, and in this case ignoring your change. All you need to do is add a property node to the end of that sequence that is Key Focus and set it to false

Passing values between event structure cases

Hello everybody,
I have a question concerning the event structure - how to pass values (let's say a string / the state of a boolean control / the value of a numeric control value / an array of numeric values) between event cases ?
There seem to be 2 situations here :
- when you need to pass the value of the control that triggers an event;
- when you need to pass the value of a control which is modified in an event case.
I have read the documentation but i still do not understand very clearly how to do this. Maybe you can point me in the right direction (maybe some threads on the forum that i have missed).
Thank you very much !!
(KUDOS for everyone who is interested in this )

AndreiN2014 wrote:
- when you need to pass the value of the control that triggers an event;
- when you need to pass the value of a control which is modified in an event case.
The first question isn't worded very well. What exactly are you looking to do? Are you looking for an event that specifically relates to that control? If so, just drop it inside of the event and wire it. Are you looking to trigger multiple events from the same control? Ie, you hit the control, event1 is triggered which then triggers event2 ... ? If so, you might consider taking a look at a different architecture. I can think of very few cases where I'd prefer do this over something like having the button trigger a state and using the state machine architecture.
Others have pointed out the Shift Register. This is the typical way to pass values between one iteration of a loop to another. We can assume you have some sort of loop outside of the event structure to make it run a second time. Put a shift register on this loop and the value wired into it will pass each iteration. But, if it's just a random control, you can also just leave that outside of the event structure and wire it in as well. This will provide the new value to the next occurrence of the event structure.
You really need to define your problem before trying to solve it.

How to use "Value signaling" for boolean-latch button?

Hello,
i hava an event-structure with a boolean-button on it (Mechanical Action: Latch when pressed).
For this button i have an event "Value Change" - works all fine.
Now i want to execute this event from an other event by sending a True into the Property-Node "ValueChangeSignaling" of this button.
But now labview tells me:
When a Boolean control has a latch mechanical
action, you cannot use the Value property to read or write its
value.
What can i do now to execute the existing event of the button?
Thanks

The reason the latched boolean cannot be set via Value property is described here:
http://digital.ni.com/public.nsf/allkb/0774F8F0498017B886256F080066E2E3
A little further info from the help:
Note You cannot use any latch action for objects with a local variable. The first local variable to read a Boolean control with latch action resets its value to the default. If you configure your Boolean value with a latching mechanical action, the Value Property and the Value (Signaling) Property always return an error. Due to race conditions that can occur when you have a Boolean value with latching mechanical action, you cannot programmatically read Boolean values that are set with a latching mechanical action.
So your options are to either change the change mechanical action to switched, and programmatically set it back to False inside your event case, or use another method to fire your event (as previouosly mentioned, consider user events).
Thoric (CLA, CLED, CTD and LabVIEW Champion)

How can I 'click' on a "latch" mechanical boolean in an event case?

Since I can't set true of false to the local variable of latch mechanical boolean, how can I click the boolean in an event case?

LUX_ wrote:
1. I can't make the value change event work (the second option of the solution posted by smercurio...)
2. The occurrence does not work as I thought it would be. I need to stop the timer if user change to other mode within that 7 minutes period (my test.vi set to 10 seconds).
The value change using a signaling property only works if you actually have an event assigned to that value change. You currently don't!
I am not sure why you complicate things with the occurrence. You don't need it. (the wait for occurence prevents the the loop from e.g. checking the elapsed time). THe code is way too convoluted.
I think all you need is one loop utilizing the timeout of the event as wait timer (and one to randomly cause faults). See attached for a rough draft. modify as needed. As you can see, you don't need all these locals and hidden controls.
LabVIEW Champion . Do more with less code and in less time .
Attachments:
testMOD.vi ‏18 KB

Is it possible to trigger the next event from within the event case?

I have a rather complicated event that is triggered by a change in value of a particular button in the interface. In some cases, I want to alter that button's value when handling other events. But when I do this, the event handling a change in value for that button does not get triggered. Is there a way to make sure the value change event gets handled at the next iteration of the while loop in which the event structure sits?
Solved!
Go to Solution.

Hi Mike,
Thanks! I was using properties and did not previously know what the value(signaling) was. Knowing this will really help me clean up a lot of redundant code.

Initial Event Case

I am using an event structure to handle all my front panel controls. I would like to have an INIT event case which will initialize all the front panel controls to a specific state. I can't find an event to trigger on. There are events for close, but I am surprised to not see a "start event". Any suggestions on how to create a "start event". Thanks in advance.
Jim@BMC

The best solution depends a little bit od the details if your program.
If the initialization should set the controls to a defined state only at the start of the program, the initialization does not belong inside the loop, but should happen before the loop.
If initial calculations should run so the indicators are also updated from calculations with the new control values, you could use the timeout case solution mentioned above. It is somewhat limited, because the timeout case might be needed for other stuff and you might actually want to fire other cases (see below).
Sometimes you actually want to run a specific, non-timeout case. In this case you could fire some events via a signaling value property, you could even line up several of those to execute several event cases in a specific order at first run. (see e.g. the image below). You can the use the same event to reinitialze things at any later time if needed.
Message Edited by altenbach on 04-20-2008 11:37 PM
LabVIEW Champion . Do more with less code and in less time .
Attachments:
startupevent.png ‏14 KB

When is Key down event case triggered

Hi all,
In event structure there is an event <this VI> key Down?
When will this event be triggered... i.e will this event be triggered only in case of a keyboard entry... ?
Or in case i use a barcode reader, if data gets populated in a control on the Front panel through the barcode reader will this trigger this event...?
Thanks

The Key Down event will only be fired when a key is pressed on the keyboard. If you want to fire an event off of a Front panel control, you can either use a User Event or a property node called Value (Signaling). This property node will cause a Value Change event to trigger when the value of the Front panel control changes.
Cheers

Event case with non-user action

Hi
I'm actually using LV8.0.1.
With this and older version of LV it wasn't possible to get an event case fired without an user action. (for example by changing the value programmatically.)
Is it possible in LV 8.2?
Regards
Yves

Yves,
You just missed the property node in your right-most loop. To create a property node, right click on the block diagram control->create->property node, and then select "Value(Signaling)". Value(Signaling) is different from "Value" in that it "signals" to LabVIEW that a change has been made, and thus an event can fire. See the image of the code in your right-hand loop.
Hope this helps!
Message Edited by Day on 10-11-2006 09:29 AM
Attachments:
Value Signalling.jpg ‏6 KB

How can I use the same event case for different controls dynamically

OS: Linux 2.6.24-1-686 #1 SMP Sat Apr 19 00:37:55 UTC 2008 i686 GNU/Linux
LabVIEW: Version 8.2
I have a lot of (about 50) controls (numeric, boolean) on my front panel. If a "Value Change" event will be fired by any of them the same event case shall be executed. As I do not want to add all 50 controls to the same event case manually I am looking for a way to do it at run time. Additionally the VI is still under contruction, i.e. controls will be added and removed.
Thanks for any help here.
Regards,
Johannes
Solved!
Go to Solution.

Hi Johannes,
collect all your control references (you can use the FP property for it) and create a user event. Connect this user event to your event structure. Now you have one event case for all your controls. See the attached picture.
Mike
Attachments:
Unbenannt1.PNG ‏11 KB

Event case: number of runs of a single event ?

Hi everybody,
I'm working on a CCD acquire system, and I developed the control software using an event structure.
Every event controls a setting function for my system, and placed in timeout event fucnctions to get the status of my detector.
Data acquisition is one of the control events. Now I need perform multiple acquisition and save acquired datas to a spreadsheet file, wich must be called with the number of the iteration.
For example for 10 acquisition, the acquisition event will run 10 times, and save 10 files named: 1.csv, 2.csv ...
How can be built a counter wich gives the number of iterations of a single event (in example the number of runs of the "acquire data" event) ?
Thanks in advance
Eugenio
LabVIEW 2011
Solved!
Go to Solution.

Thanks, value signaling vas the right choice. I've wired the increment function to a shift register function of the while loop wich contains the event structure.
Placed an indicator inside and works fine.

Are you ever required to wire the dynamic event terminals through an event case?

I remember some time ago, I ran into an issue while using an event case where my program was not functioning properly until, on a whim, I wired the dynamic event through that event case... now the reason I'm asking this in a general sense is because I don't remember what particular code I had this issue with and I could have been failing to update a shift register or something.
In code I'm currently writing, I'm simply passing the dynamic event wire in a shift reg. I was just wondering if there's any difference between wiring it through the event cases or simply passing it to the output shift register (without passing through the event cases)...
any info appreciated!
Thx
-pat

You do not have to wire it through. You don't need a shift register for references since the value will be the same for each iteration. In fact using a shift register is probably what caused issues. You probably updated it with the default value somewhere.
=====================
LabVIEW 2012

Save for previous 2009 -- 8.5 with value signaling

I have the following VI, that is an example for a friend of mine. I am not sure if the property "Value signaling" is in 8.5, but if it is not, I would not expect a crash, rather a warning or something to that extent.
Error:
Attached is the simple example VI in both 2009 and 8.6 (which saved fine) If someone could take it down to 8.5 (if possible), I would appreciate it.
Paul <--Always Learning!!!
sense and simplicity.
Browse my sample VIs?
Solved!
Go to Solution.
Attachments:
valueSignalingExample2009.vi ‏16 KB
valueSignalingExample8.6.vi ‏11 KB

Hi Paul,
LV2009 has the (known) problem of saving VIs with an event structure back to previous versions prior to LV8.6...
Message Edited by GerdW on 11-24-2009 09:38 PM
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome
Attachments:
valueSignalingExample_85.vi ‏19 KB

Lock front panel until the event case for this event completes

A Dynamic Event is a filtered event? Is this why "Lock front panel until the event case for this event completes" is not shown on Edit Event window dialog? I use Dynamic Event so I can subvi the event structure.
I need stop my app from locking the FP whenever the user double clicks on the numerical array value (<-- the FP freezes the mouse and renders it useless) and stops the value from ever being changed. This event is registered for Value Change (not mouse up or down) and I get a locked mouse. As yet in the UI, no value changed occurs but I get a locked mouse. A LV bug?
Trying to KISS, I can see this fixing this by moving ONLY the value change event to the top level VI instead of a dynamic registered event in a subVI. This will give me the option to NOT "Lock front panel until the event case for this event completes" .
Solved!
Go to Solution.

richjoh wrote:
Thx, Ben that fixed the problem when I unchecked "Lock panel...".
So it appears LV locks the panel during runtime once the Dynamic Reg Events is on BD and it doesn't matter if your case to handle the Reg Events is created or NOT... interesting. That's why my mouse persisted to "freeze up" although I deleted the case for my FP array.
Its situation like what you described that has given me many insights into how LV actually works. In one of my bbuggy VI's I found that a class wire can run a million miles through multiple sub-VI queues etc but the data itself is only touched when it has to be touched. in my case it was a crash while trying to write bogus class dat to a TDMS file.
I am glad you are back on course.
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Value Signalling Event Case

Similar Messages

Maybe you are looking for