07-13-2010 06:06 AM
Hi,
i've a problem concerning analog to digital conversion using my spartan e3 fpga.
I set the PreAmp as recommended in the User Guide and want to start analog to digital conversion.
I also disable the other SPI devices in order to read out the MISO properly. But when i've no signal neither on
ADC A nor on ADC B i can read out values, which a different from zero. And the most confusing thing is, that
the values are changing with the time.
I also use a 34 cycles to read out the data properly.
Best regards,
Steve Ness
07-14-2010 10:34 AM - edited 07-14-2010 10:39 AM
Hi Steve,
an analog-digital converter needs a input source with a well-defined impedance.
If you have an open analog input (floating) the ADC provides you with any value. Mostly this value changes slowly.
More details you can take from the following documents:
Troubleshooting Unexpected Voltages, Floating, or Crosstalk on Analog Input Channels
http://digital.ni.com/public.nsf/allkb/B9BCDFD960C06B9186256A37007490CD
You can test the analog input with a battery.
I hope this helps.
With best regards,
Ralf N.
07-14-2010 11:04 AM - edited 07-14-2010 11:06 AM
BTW:
A ready to run example for analog input is included in Exercise 4.1 (see Solutions folder).
LabVIEW FPGA Module Training for Xilinx Spartan 3E XUP Hardware
http://zone.ni.com/devzone/cda/tut/p/id/6848
07-14-2010 01:56 PM
Thank you for your help. In fact is my analog input floating.
I'll tell you what the problem was.