How to use the ADC/DAC on the NI ELVIS FPGA Board?

[Melanie Binggeli]

Hi!! I'd like to use the DAC and the ADC on the NI ELVIS II Digital Electronics FPGA Board with LV FPGA.

I saw, that we have low-level access for the DACs and ADCs (Amplifier, SPI etc). I’d like to use the ADC and DAC directly. Do we have any high-level access for this converters?? Or any example (with an explanation) how we can use the converters with the available low-level API??

Thanks a lot for your help!!

[Andrew McL · Accepted solution]

Hi NI-Elvis_forTheWin,

Thank you for contacting National Instruments. If you have installed the Digital electronics driver then you have actually already installed the example files as well. These are located at the following location:

c:\program files\National Instruments\LabVIEW 2009\examples\DE FPGA Board\

The examples that you need are the Analog In and Analog Out.

Best of luck with your application.

[Melanie Binggeli]

Hi Andrew!

Thanks a lot for your fast and friendly answer.

This examples are fine and they solve my request.

Great service!

[DWing]

It's a shame there's not a word about the ADC/DAC on the elvis FPGA board documentation (a part from that they are present), and the few tips about them are also wrong (ADC is 14 bit not 12, as one can infere from the "example", or better, from the component data sheet. Oh yes, what is the component part number? not even a word or link on third part documentation). 

Fortunately, it seems like the part numbers for the pre,ADC and DAC are the same used in the Xilinx Spartan 3E starter kit, for which exists plenty of documentation. ( I never immagined myself giving a positive remark on xilinx documentation). Can one assume the circuit also is set up in the same manner? (input signal dynamics?)

Since it is stated in the user guide the user can profit also of the Xilinx ISE IDE, why aren't reported ALL the FPGA pin constraints for .ucf file? (ADC??DAC??PRE??). Ok, I know, I know... I can look up in the working directory where labview makes the "examples" compile...Anyway, in my opinion, that's not the way a designer should strive.

I think the user must be provided AT LEAST with the references to gather the minimal information to make the PAYED hardware work.

I expected something better from NI. In my opinion no example can sobstitute at least a brief documentation.

[DWing]

... Just in case anyone else is using this board trying to make the ADC work, and to be a little more constructive: be the designer warned that the Analog_Input example provided with the board driver in place of the documentation is not working, as one can easily verify testing the application with, for example, the built-in Elvis Variable Power Supply.

That's because the project contains AT LEAST 3 errors:

- in the AI_Read.vi

when calculations are carried out for the output "value A" (and value B as well), inside the "check the sign" case one should subtract 8192 not 8191 (ref to wikipedia two's complement to check). I would also consider to exploit the properties of the "boolean to array" component (near "to number" label) to perform these triky operations for you...

- in the  test_AI(host).vi

The range of the ADC is +/- 1.25 V, and the ref voltage is set to 1.65V. This means the range of ADC (with gain set to -1 by pre-amplifier.vi) is   0.4V to 2,9V

SO: each DAC step is [max-min]/2^14 = 2,5/16384

and not

3,3/16382

Change this and you'l find the VI now reads the correct tensions in the working range of the ADC.

finally, to help you with some documentation, search for the xilinx spartan3E starter kit user guide. The ADC part is exactly the same on your NI elvis FPGA board and is well described.

Hope it will help somebody

DW

[mohamed_alasklany]

you are right