signal demultiplexing

[Ibrahimlee]

Dear Sir/Madam

I’m a researcher in De Montfort University, Mechatronics group, and I have a program difficulty using Lab view.

I’m working in human tracking and identification within the home environment and I’m using many analog pressure sensors (up to 500 sensors). I want to acquire these signals and send them to the computer. For that reason, I’m using external multiplexers IC (ADG406) connected to a computer through NI 6052E DAQ card (Inputs: Multiplexed analog signals, outputs: multiplexer control signal).

 My problem is that I can’t find the suitable function block that demultiplex the input signals, save these signals in files, and make synchronization between the computer and the multiplexer.

Thank you for your attention in this matter.

Kind regards

Ibrahim Al-Naimi

[Owen.S]

Hi Ibrahim,

I've been looking at your problem and I have some questions about your setup. How have you connected all of your sensors and multiplexers? There isn't any specific function block to demultiplex signals so you will have to write something to do it. I assume you have your multiplexer control signal connected up to the digital lines of your card? If this is the case you can use the 4 bit binary address lines to select which signal you want to aquire and passing this to all the multiplexers (Providing you only need to read from one sensor at a time). I have found this forum post on a similar subject which I hope might help you:

http://forums.ni.com/ni/board/message?board.id=250&thread.id=31136&view=by_date_ascending&page=1

Incase you haven't connected up your sensors and multiplexers yet, I have a couple of ways you could do it:

(I looked up your multiplexers and I am assuming they are 16 to 1)

With the current hardware you have, you could connect 15 multiplexers straight into the DAQ card, then use the 16th to connect to a further 16 multiplexers. This way you would have two "banks" of multiplexers and a theoretical maximum of 496 sensors. You would then use the DIO lines to control which bank you would use.

If you wanted more sensors than this then you would have to buy another DAQ card. Then you could fit two lots of sixteen multiplexers into the cards and theoretically get 512 sensors.

Let me know if you need anything else explaining or have any further questions.

Thanks,

[Ibrahimlee]

Hi Owen,

Thank you a lot, you gave me a very good start. Unfortunately, I still have a problem. The for loop is very slow that I can’t scan all the sensors value quickly. I need high speed demultiplexing process that I can sample al the sensors in acurrate manner.

In my application, I need to scan the sensors value continuously, chase the sensor value variation and save the analogue signals in files for processing. I have connected just 16 sensors with one MUL (16-Channel) and I did the following program:

Please, could you tell me how I can speed up this process.

Regards

Ibrahim

[Owen.S]

Hi Ibrahim,

The best way I can think of to speed up your VI would be to replace your DAQ assistant's with low level DAQ functions. There are lots of examples of how to do this in the LabVIEW help:

For your first DAQ assistant this guide may help: 

Step 1: Go into LabVIEW and go to help.

Step 2: Click "Find Examples"

Step 3: On the browse tab, on the tree table click "Hardware Input and Output" > "DAQmx" > "Digital Generation" > "Write Dig Chan.vi"

and the second, have a root around in the Analogue folders in DAQmx on the same tab as above and there should be some more examples in there.

Using low level DAQ functions will speed up your process because the DAQ assistant is an express VI and has alot of other things it does which slows the read and write time down.

Let me know how you are getting on and if you need any further examples on the DAQ functions.  

Thanks,

[Ibrahimlee · Accepted solution]

Hi Owen,

Thank you very much for your help, i have just solved the problem. I have decreased the samples number and increased the sampling rate frequency and every thing is going well.

Thank you again for your support.

Regards

Ibrahim

[Owen.S]

Hi Ibrahim,

No problem at all. I'm glad you got it working.

Thanks,