problems with DAQ on PDA with CF 6004

[eran atlas]

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6. Wireless connectivity:

a. WLAN(802.11b)

b. Network standard IEEE 802.11b

c. Data rate 1Mbps, 2Mbps, 5.5Mbps, 11Mbps

d. Modulation   : CCK(11 Mbps , 5.5Mbps) , DQPSK (2Mbps), DBSPK ( 1Mbps).

e. network architecture : ad-hoc and infrastructure.

f. Operation frequency : 2.4-2.497GHz

[eran atlas]

continue(3)

g. operating channels : 1-11 ( north america), 1-13 (Europ and Japan).

h. RF output power : 13 dBm maximum.

i. range : indoor - up to 10 m at 5Mbps, and 75m at 0.5Mbps.

j. client utility: automatic location profile, site survey, diagnostics, current link startup, ping.

k. software support : Wi-Fi certified.

l. bluetooth wireless technology : 2.4 GHz ISM band operation; compatible Bluetooth 1.2 wireless technology; includes manager for Bluetooth with wireless technology; class II device; Max 4 dBm o/p power; 3.3 v operation; UART interface.

[eran atlas]

Sorry it took 4 message to send the specs , the system woudn't let me send it all in one message.

Thanks again for all your trouble,

I hope you'll able to help me

Eran

[Laura F.]

Hello Eran,

Thanks for the information.  I have modified a second VI to basically do the same thing, this time with a finite acquisition.  Please try running it on your PDA.  You will need to open the NI DAQmx Base Configuration Utility from the LabVIEW Tools menu and modify the task "ai finite buffered".  Enable all four channels and change the rate to 250 S/s.  Make sure that the CF 6004 is showing in the drop down menu and you save the task.   I think that I have heard this before, but just to verify - you are using NI DAQmx Base 2.0, correct? 

Download the program onto the PDA and make sure that the task is shown in the drop down menu and run it.  What happens?

Thanks,

Laura 

[eran atlas]

Hi Laura,

Well the file you sent me works better, no delay, but the data is presented in a very cut way ( the change of the data is not so smooth). it looks like the data is sampled in 1Hz rate. can I change it so it will be better? , Is this just the way the data is presented but the real sample rate is faster?, how can I check it?

I am using DAQmx base version 2.0 . I changed the VI so the sampled data will be stored into a file ,how can I add a "time" colume to the file so I'll able to check the real sample rate?

Thanks

Eran  

[eran atlas]

Hi again ,

1. What is the size of the buffer ( on the card) , I search the mannual and it isn't written there?

2. I check the sampeling thing , and I think there is a problem with the outer loop, It doesn't go fast enogh so I miss samples between each iteration.

May be we could talk ( Skype , username : " atlaseran" ).

Eran

[Laura F.]

Hello Eran,

I am sorry, but we'll have to keep our discussion on the forum.  The buffer size is listed in the specifications document for the CF 6004 as "input FIFO size" and it is 8,192 samples. 

After obtaining hardware that is closer to what you are using (PDA + 6004) I have found the following things:

1.  The PDA does not possess enough processing power to acquire continuously from the 6004 AND graph data at the same time.  I see the buffer overflow error once the graph starts to scroll.  There may be some graph settings that do not exhibit the problem as much, and I am going to try to see if I can find them.  Other workarounds for this problem are to use only numeric indicators, and not a graph, or to use a PDA with a PCMCIA expansion slot and a PDA compatible DAQCard.  I did not see the buffer overflow error with this hardware.

2.  The example I posted is a finite acquisition inside of a while loop.  So, each time the acquisition begins, it must start the task, acquire the data, and then stop the task before starting the sequence over again.  Because of the reconfiguration, there will be some delay between each iteration while the task is stopping and starting again.  The wait timer in the outer loop has nothing to do with this because as long as you do not click stop, the program will continue to run only in the inner loop.  Once you click stop, the inner loop stops and only then will the outer loop execute again.  The example is setup to acquire 10 samples at 250 S/s.  I have not done any processing of the data to reduce the sample rate.  So it will plot 10 samples at 250S/s, a delay for stopping and starting the task, and then 10 more samples at that rate over and over again until you click stop.  You can reduce the number of samples you are displaying each time if you want to reduce the sample rate. 

If you do not like the way that the data is being displayed, please change the sample rate and/or the number of samples to acquire to find something more to your liking. 

One thing I do not understand is why you can't just use the sample rate of 200 S/s. 

To add a timestamp to the file, use the time functions on the Time, Dialog, & Error palette.

Thanks,

Laura

[Laura F.]

Hi again Eran,

I misspoke in the above post.  I should have said chart, and not graph, above.  If I use a waveform chart and it starts to scroll, I get the error.  If I use the waveform graph, I do not get the error.  I am attaching a new VI that does a continuous acquisition and parses the data to get a lower sample rate and displays it on a waveform graph.  I don't get the error.  Try this VI.

Thanks,

Laura

[eran atlas]

Hi Laura,

I am sorry I didn't answer your message earlier, but I had several exam so I didn't tried the VI you sent me untill now.

So, It is working OK and I could do some changes in order to save the sampled data. I have two more difficulties I am hoping you can help me:

1. The VI I am trying to develop suppose to work continously until the PDA have a power problem. In order to avoid a situation when the battery of the PDA have no power and the sampled data won't be saved, I won't to measure the time ellapse since the "Run" button had being clicked , and when the it reach a certain value the insinde loop should be stooped and an error message will appeared. Is there any function in Labview that measure " time ellapse since action" ? or may be there is a function that check the batteray status?

2. In the VI you sent me there is a waveform chart which present the sampled data. However, it only presents the 10 new samples and erase the old ones. Is there any possibility that the new data will be added to the old one? It is weird , since the same block diagram in PC source VI do exactly whant I want.

I have attached the new VI ( after the changes I made)

Thanks for your help

Eran

[Laura F.]

Hello Eran,

Regarding your DAQ question, if you try to keep the chart history of all of your data, at some point in time the chart will start scrolling.  In my experience, this is where the buffer overflow would occur.  The PDA simply does not have the resources to pull the data from the 6004 and have the chart scroll at the same time.  This is why I have used the Waveform Graph instead of the Waveform Chart.  If you want to keep some history on the graph, you can save a few of the previous iterations data and concatenate them onto the most recent data and display that on your graph.  The example VI you are referring to uses the Waveform Chart and always runs into the buffer overflow problem when using the 6004. 

I will check into the timing issue and get back with you.

Regards,

Laura