LAVA 1.0 Content

QUOTE (BrokenArrow @ Nov 17 2008, 11:19 AM)

... then the global variable implementation of a semaphore is a stop sign, partially obscured by weeds and limbs, on an abandoned contry road where race conditions exist freely ...

... and a troll that live under a nearby bridge wakes up and repaints the sign depending on the phase of the moon and the house in which you will find Mars.

QUOTE (BrokenArrow @ Nov 17 2008, 09:13 AM)

Minh,

Yep, a LV2 global, like OpenG's "Data Changed" is a great tool to prevent train wrecks. I agree that the structure of the semaphore is strange. Why on earth should there be a "Not a Semaphore.vi" if the structure were not conducive to abuse and mixing with other things?

Val,

Good point! It looks like 8.6 has replaced the CIN's with Queues and other dodgy bits, and 8.5 uses CIN's. Even NI agrees that it was never necessary to begin with! (kidding).

Semaphores are very useful for controlling access to shared files. If parts of the code require continual upating of a file while another must read from that same file, a semaphore can be sued to prevent issue with the file pointer of the "read" to screw up the file writing. Under many conditions I can avoid the semaphore by putting the file I/O in an Action Engine (that is automatically protected using a mechanism very similar to semaphores) but if some of the File I/O is CPU intensive, I may be designing in additional bottle knecks. By using Semaphores to protect the file access, I can reduce the bottle-kneck to just the File I/O and nothing else.

Note: Any shared resource can be protected the same way the file is protected.

Ben

QUOTE (labviewRTS @ Nov 14 2008, 12:26 PM)

Does anyone here have an ideas on how to implement an Air Crash management System or Aircraft management system using Labview. I am interested of starting a design for this application. Please guide me what tools should I need, is it using compactRIO, FPGA or others?

Can you define the functionality and requirements of this system in a lot more detail. Then we can provide some suggestions for you. Are you planning to build this for yourself, as a contractor, to bid on a project?

Is the timed loop necessary?

Using a timed loop that fast with that much code in it is doomed to overrun it's timer. (something you don't check for).

I would read the values available, sent them via a queue element by element to a lower priority loop, that does the publishing of the shared variable.

Should the two can's read one after another? If so just place them in one frame with error clusters connected.

How you have programmed it you throw away the parallel power of LabVIEW.

What currently happens:

t->

PollC1----ReadC1----ProcessDataC1-----PublishDataC1

-----------------------------------------------------PollC2----ReadC2----ProcessDataC2-----PublishDataC2

What could happen (if you want it):

t->

PollC1----ReadC1----ProcessDataC1-----PublishDataC1

PollC2----ReadC2----ProcessDataC2-----PublishDataC2

Now if you start queueing data the following can happen:

t->

PollC1----ReadC1----SendQ1

PollC2----ReadC2----SendQ2

ReadQ1----ProcessDataC1-----PublishDataC1

ReadQ1----ProcessDataC2-----PublishDataC2

I think you will have more predictable timing schemes in the last case, give every row it's own loop.

Why do you need an RT read? The current setup does not read every 2.5 ms a can message. It reads every 2.5 ms all the can messages.

What is the observed length of your FIFO? If this increases your listener is to slow and might cause timing hickups.

Ton

In the good old days, when I was sitting in the train a lot off the administration members would have a clipping paper, with news items about their work pasted into one paper.

This can be done for LAVA as well, what if your boss isn't to keen on you visiting LAVA all the time?

Use Tabbloid, that sends you an PDF news letter of RSS feeds.

Here's a LAVA example.

Ton

(attachment removed due to email address)

Dan,

here is some little optimization of your code limiting the runs of the for loops.

Ton

PS I advice you to use the Code Capture Tool for code captures.

QUOTE (Ton @ Nov 12 2008, 09:00 PM)

I read through the topic, only the first post has a question about code, and has little no interpunction.

Interpunction does not mean all in capitals, write sentences and questions, take the time to write a question.

Write it in notepad (not Word or an HTML editor), save it. Wait half an hour, open and reread.

Do you have clear questions, if so post them.

QUOTE

The code posted in the first post is two weeks old, what is the current state of your code?

QUOTE (kmc @ Nov 13 2008, 02:31 PM)

Just start with one station, duplication of code is easy.

QUOTE

Go over the points you have posted step by step.

Post the current code with references to every point mentioned here.

Good luck

Ton

QUOTE (MJE @ Nov 13 2008, 02:12 AM)

Also, here's one for you: why does a double need to be coerced to a double?

http://lavag.org/old_files/monthly_11_2008/post-11742-1226538019.png' target="_blank">

I think your data out is a typedef (and all the wires inside the while loop as well, where the 'Value' isn't one.

Ton

How wonderful it would be if such things could be arranged I am not aware of such a solution. Yours is the most elegant I can think off.

Could you do me a favor?

Save everything, close your project, then close the VI owning the XControl.

I have an XControl locking everything up (LabVIEW 8.2 through 8.6), NI R&D refused the bug because I couldn't isolate it (That is their job, sorry).

Ton

QUOTE (Michael_Aivaliotis @ Jun 2 2008, 08:04 PM)

homework hustlers is an Excellent tag!

RiotRiot

QUOTE (TobyD @ Nov 12 2008, 10:11 PM)

Sorry I thought you meant to. (sincerely)

QUOTE (crelf @ Nov 12 2008, 10:27 PM)

I only use the report button with spam. All other posts are somehow on topic.

However I used a rather brutal tag http://forums.lavag.org/sensor-calibration-test-t12296.html&p=54305#' target="_blank">here, it is somehow a way to express my feelings on the post.

Maybe I have crossed the line with that one, however I believe HH is a good tag. I had the feeling we are not homework helpers and had a policy on that. Tagging a post with Homework Hustler warns other people not to give a full blown solution, but learn them to fish.

Ton

QUOTE (TobyD @ Nov 12 2008, 09:28 PM)

This doesn't seem to be working for me (Firefox 3.0 or IE8 on Vista) but I think it would be useful to guide people to use the same tags.

I tagged a HH a few days ago and now the tag is gone - was that the poster deleting my tag, or are only admins allowed to post "negative" tags? Too bad you can't lookup the tag history for a given post since anyone can edit them.

I deleted your tag.

Ton

Post-count is important.

Lurkers are losers!

Ton

PS should we add this to the Forums guidelines?

Ashwin, have a look at the guidelines for this forum. Moreover learn to ask questions the smart way.

I read through the topic, only the first post has a question about code, and has little no interpunction.

You have not added any code, we have no idea what actually is your problem and current state of your coding.

All these things together hold me back in helping you. LAVA is not a LabVIEW solution center.

Ton

Now where is the good coffee?

Well I'm not exactly a lurker but look who just crossed over from the dark-side!

Ben

QUOTE (sachsm @ Nov 10 2008, 11:42 PM)

A XControl has both a Label and a Caption but it is not apparant which control reference it is attached to.

The Container State.Refnum cluster element in the Facade VI returns the reference to the control on the owning VI pane.

More info in the wiki on http://wiki.lavag.org/XControl:Abilities:Facade_Ability_VI' rel='nofollow' title='LabVIEW Wiki article on XControl:Abilities:Facade_Ability_VI' alt='Wiki article on XControl:Abilities:Facade_Ability_VI' style="border-bottom: 1px dotted #3366BB; color: #3366BB; cursor:pointer; text-decoration:none;" class="wiki">XControl:Abilities:Facade_Ability_VI.

Ton

QUOTE (sachsm @ Nov 10 2008, 03:31 PM)

Does anyone know if it is possible to programatically access a xcontrols label text property. I have looked far and wide but cannot

seem to find out how it is stored.

Thanks,

Please pardon my ignorance (I don't do XControls every day) but I thought we had to explicitly code every method we wanted to use for an XControl.

Ben

QUOTE (Yair @ Nov 9 2008, 01:16 PM)

I can't look at the moment, but are you sure the toggle switch only responds to clicks on itself? It's quite possible that it has a bounding rectangle which is simply close to the graphic. Anyway, even if it does, it is implemented in C using vector graphics, so you can't duplicate that exact effect. You can import vector graphics into LabVIEW, but I don't remember if it does what you want. You can see more about this http://forums.ni.com/ni/board/message?board.id=170&message.id=231915' target="_blank">here.

I can confirm that for you. I have been using your technique published in the Nugget you cited with wmf files I create using PowerPoint so that I can specify the transparent color.

In fact it alomst work "too good" if your graphics are mostly transparent, you will find that it is mostly a pain to find a sweet spot.

Ben

QUOTE (MJE @ Nov 6 2008, 05:34 PM)

Note this can lead to annoying behavior while in development mode, so I usually do something like this:

App.Kind = Programming > Application Control > Property Node, then select Application > Kind.

One of my application is running on the server computer which is located remotely.I was trying to access LabVIEW panels using URL created for the application and i was not able to access the panels and i was getting the following message,

requested VI is not loaded in the memory on the server computer

Can anybody help me regarding this problem

regards,

Naresh.N

Hello every one!

i wanted to hire virtual employees for web designing and SEO. Actually i am looking for whole virtual team. Because now it's become very expensive for our organization to recruit employees And we need reliable and quality virtual employees.

We were prepared to post our requisite on freelancers’ site. But we have observed that it's very time as well as money consuming process. And also I heard that “The bigger problem on Elance, in my experience, is dummy projects. Some buyers post projects simply to get an idea of the cost or to try to find free work” So, what next?

Our team comes out with conclusion to directly contact companies who are providing virtual employee services. But the question is "RELIABILITY and Hiring charges".

We have got replies from some forums and communities. So, now we have one option company www.marketraise.com. it's nice.

But we want best service provider with better package.

Thanks in advance

Sophia

Today I sat down and wrote an application using LabVIEW.

This thread is feeling like Twitter.

QUOTE (bono02 @ Nov 2 2008, 03:48 AM)

Hi Ton,

Thank you for your reply. However, I could not find example in ni.com related to auto-initialize function.

Could you give me one example?

Or perhaps what you meant was the create instance function (like constructer in C++) in LV Object Oriented Graphical Programming,

was this what you mean?

No, I wasn't very clear.

QUOTE

That's close, but not entirely, what I mean is to use one of the clounters as a clock source.

An example shipped with LabVIEW (examples\DAQmx\Synchronization\Multi-Function.llb\Multi-Function-Synch Dig Read Write With Counter.vi) shows how to use a counter as a clock for a read and write routine, just remove the read or write to fit your needs.

Remember this can only be done on port 0 (which has 32 inputs on the 6259).

Ton

PS, if you post screenshots of your code I recommend you to use the http://wiki.lavag.org/Code' Capture Tool' rel='nofollow' title='LabVIEW Wiki article on Code Capture Tool' alt='Wiki article on Code Capture Tool' style="border-bottom: 1px dotted #3366BB; color: #3366BB; cursor:pointer; text-decoration:none;" class="wiki">Code Capture Tool

Hi,

Are you using IMAQdx and IMAQdx

If youre using the snapshot VI then probaly thats the problem. This Vi only allows you to get one image at a time (using a lot of time to do so). Perhaps a better idea is to use the low-level Vi. First open a session to a camera, then configure it (set the mode the continuous and set a large buffer), then start the aquisition proces. The camera will now send a continuous stream via DMA into the NI(ring)-buffer with the set size. Now you can use the GetImage VI to copy the image from ring buffer into a user image and proces it. The camera will stream

Hi,

Are you using IMAQdx and IMAQdx snap function?

If this is the case probaly the snapshot VI is your problem. This Vi will only bring you one image at a time (using a lot of time to do so).

Perhaps a better idea is to use the low-level Vi. First open a session to a camera, then configure it (imaqdx configure aquisition.vi). Be sure to set the mode to continuous and setup your buffersize, then start the aquisition proces (imaqdx start aquisition). The camera will now send a continuous stream of data via DMA into the NI(ring)-buffer. Now use the imaqdx getimage.vi to copy a image from ring buffer into a user-image and proces it. You can select the image you interrested in (buffer number, last (n) or next (n+1). If your processing is faster then your processing (for CCD normaly below 40ms) you can proces every image on-the-fly. If it takes longer you need to setup the image buffer large enough, and copy the image out on a lower rate using the buffer number.

Dont forget to stop the data stream from the camera using imaqdx stop aquisition and close the reference at the end of your application.

These two examples would be interresting: [Low-Level Grab Async.vi] and [Grab and Detect Skipped Buffer.vi]

Regards Patrick

Hi Dan,

Because you are using a webcam (probaly cmos), I would advise you not just to compare the images pixel for pixel. CMOS cameras mostly have a lot of noise so you have illiminate that first. Make a so called kernel (n x n matrix) that calculate average value of those pixels. In IMAQ you can do this with a filter function.

Alternative you can divide your image into sector (e.g.32x32 pixels) and check for differences using a threshold for each sector, then threshold on the number of changed sectors.

Lots of succes

Patrick

You could build an auto-initialize function, in the first call you create and start the task.

In succeeding runs you only read the DAQ.

However I advice you to timed IO within DAQmx, so the timing is handled by the daqmx driver and not by LabVIEW.

To do this you should create a clock on your 6259 of 5 ms, and do a burst read in LabVIEW of 1 sample, no timing needed the speed will be limited by the DAQ card.

Ton (look at the NI examples for timed IO)