Simulate event structure in LabVIEW base?

I have a LabVIEW base version (v8.6) which does not have the event structure. I found it was quite inconvenient to monitor the status of several controls (the action after click a control depends on the status of other control(s)). Especially if I want to add another function (control), the effort increase exponentially with the existing number of controls
I got an idea of simulate the event structure using 'Shift Register'. First, I will bundle all the values of controls into a cluster. Then I will put the cluster in a while loop, and compare the value of the cluster with its previous value (xor the shift register). If the compare result is false (none of the control is changed), the program goes to next iteration. If the XOR result is true (one of the control was changed), then the program goes into event handling code (it will pass which control has changed, and the whole cluster). So for each control change, we can write a independent code to process the event. After processed the event, the event was cleared.
The following is a section of my ugly code currently used to monitor several controls. And I am thinking of rewrite it using above idea so that there will be less likely a hiden bug.
Any comments of suggestions?
Message Edited by RyanWu on 10-23-2009 10:16 AM
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UglyLabVIEWCode.png ‏18 KB

Ben wrote:
Altough this is an interseting academic question, we really can't duplicate the efficiency of the Event structure so springing for an upgrade is highly recomeneded.
But I am not here to sell LV but rather help LV developers so...
Start by developing an Action Engine with the following actions.
1) Init -caches control ref for all controls and indicators for which you need an event. Optionally rest them and cache their state.
2) Check - Will compare the current state with the prvious state and any changes get pushed onto a stack in the AE and if there are elements in the stack (due a change detected now or one left over form the last check) and returns a type-def'd enum describing what changed. Multiple changes should be on the stack for next time.
3) Get New - will return the new value of the value requested via an Enum.
In you top level VI use the AE to Init before you run and then use an "Check" method to se if anything changed. If it flags a change (boolean output of AE) then the Enum is used to select the proper case of a case structure. Inside the psuedo-Event case, you can use teh AE with the "Get New" action and pass the enum to choose which value to get.
It is hardly an Event Structure but it should come close.
Ben
But after looking at Knickerbocker's* post we can go farther.
Put the above code in a sub-VI that feeds a queue. Then you can monitor the queue for updates just like in an event structure AN you can queue up all of the changes at once and can ingore my mention of caching the change methods in the AE. Just let the queue handle the stack.
Ben
*Kudos for inspiration!
Message Edited by Ben on 10-23-2009 10:54 AM
Ben Rayner
I am currently active on.. MainStream Preppers
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Alternative to Event Structure

Hi,
I am an EE intern creating a testing program for an antenna pedestal. I am using LabVIEW Base Version 11.0.1.
I am using an LV-Link VI provided by an example from the download for the Data Translation 9836 module that my company is using. Currently, I have an array correctly storing data when the user presses the "Start/Stop" button for the first time. I am working on the section of my VI where I prompt the user to "Save Data to File?" so that I can make the VI either save the data when the user clickes "yes" or stop acquiring data and not saving the data when the user clicks "no".
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I saw another thread with a similar problem here: http://forums.ni.com/t5/LabVIEW/Simulate-event-structure-in-LabVIEW-base/td-p/1008900, but I am having a hard time understanding what exactly is going on since I just learned all of the basics and am figuring out LabVIEW as I go along. If someone could help me simulate an event-structure-like situation in my VI that I have attached, it would be greatly appreciated.
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Attachments:
Compact Range Controller.vi ‏43 KB

At the moment, the code is still way too scattered. I meant one of multiple states of a state machine. From the current code, I cannot really tell what you want.
Maybe all you need to do is delete the orange wire in the FALSE case of the upper case structure and make the output tunnel to use default if unwired. (but make sure you don't lose the data).
Attached is a quick modification that gives you another additional true whenever the button changes. Used it to either clear the array or execute the "save" case once.
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Attachments:
Compact Range ControllerMOD2.vi ‏37 KB

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Are these test questions? I could name 10 for each, but why are you asking?
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I am new to labview, having recently taken the Core I and II courses.
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Attachments:
Front Panel.vi ‏115 KB

A few comments to your VI in general:
You changed the stop button to "switch until released", most likely because you fabricated a race condition and did this as a quick fix. The reason is (1) your placement of the stop terminal outside the event structure and (2) the use of a local variable wired to the stop condition. The button terminal of a latch action boolean belong inside it's associated event case! This way it gets read (and reset to false) when the event occurs. In your case, the local variable and the button get read before the event occurs and the loop needs to spin once more at the event that occurs when you release it (true->false). At this point, the local is still true from the earlier event and the loop stops. Correct would be: latch action, stop terminal inside stop case and wired to the stop condition from inside the event. Other cases use the default output (false) and don't stop the loop.
Your "equal false" code fragment is just an invert, right? So why complicate things?
Why do you need a wait if there is an event structure?
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I did not. Is there any better chance for it to be caught there by a NI eye than it is in the LV forum? I though these threads were deemed to gather bugs/features that had been already acknowledged by NI with a CAR number.
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HMI.vi ‏33 KB

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James.Morris wrote:
Ah, you're only one release away from the event structure. That's too bad.
You're going to have to implement a Polling loop that continuously checks the user inputs. Make sure you add a Wait function to the loop (~100ms) because that will act as your chance for the user to make changes. You can use shift register(s) to keep the previous loop's values and compare to get a bunch of Value Change booleans. If you want a specific case for the specific events, then you can group all of your Value Changes in to an array and act upon the ones that are True via a Case Structure.
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James, I swear I'm not picking on you today
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6.i didn't have a "Value (Signaling)" property- (a subject of some CLAD exam questions not that you suggested it)
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On to licensing options. (Not a lawyer! consult your Legal Dept!)
If you are not doing work towards earning a educational certificate you should not be using Student Edition. And, in some cases (Like working on a student project with commercial investment) not even then!
The Home Edition is also a new option. It is intended to enable fast "Proof of Concept" development or development for your sole non-comercial use.
LabVIEW Full and Professional are for comercial use and have a "Home Use License Agreement" clause attached. If your company owns a LabVIEW License you CAN install a copy on a "Home PC" for the limited use of aiding your employer (who paid for the license) such things would arguably enclude "Training"
NI is not totally opposed to negotiating "Exceptional" agreements for mutually beneficial reasons. Youl'd better bring a justification better than "I can't afford it" Go find some investors and buy a license in that case. And Yes, until the moderators take this down, I did at one time have a LabVIEW license for exclusively engaging the LabVIEW Community (Forums and NI Sponsored events use only- LAVA was not encluded) I'm not sure if such a deal could be negotiated in the future. In Fact, The Home Edition would have been less costly.

LabVIEW 2012 while event structure cannot stop

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Please see the attached VI.
Thanks.
Solved!
Go to Solution.
Attachments:
Close VI prompt.vi ‏9 KB

Yep, something is wrong. You need to add a event case to detect a value change on the stop button.
The thing is now your event structure keeps waiting for one of the event that it handles, and ight now it only handles the "panel close" event, the "timeout" event is handled too but since you haven't connected anything to the timeout terminal (top left corner of the event structure) the timeout is -1. So when you run the VI the while loop is stuck in the first iteration and waits for a panel close, the stop button will only be taken into account after the even structure catches an event ; I think this is because LabVIEW will execute code linked to the stop terminal of the while loop only after all the rest of the code in it has finished executing.
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Aaron1978 wrote:
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Bernardino Jerez Buenaobra
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Telephone:+632772-4941-43
Fax/Data: +632772-4944
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Simulate event structure in LabVIEW base?

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