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Using FPGA for Digital Feedback Applications


rbharvs

Question

Hi, I'm looking to use the Nexys 4 board to implement PID control. In order to do that, I need to make use of the on board ADC. Unfortunately, I've had very little luck finding any information on how to use the on board ADC. I've read older posts on here that ask similar questions and none have been helpful. Specifically, I want to know exactly how to use Vivado to set up the ADC so that the FPGA can sample two separate analog input signals. I would very much appreciate the opportunity to speak directly to any Digilent technical support or engineers; phone would be best. Otherwise, any other input would be appreciated.

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Yes, the original linked page was describing the nexys4-DDR version of that project, and the binaries will definitely not work on the Nexys4 (the entire pinout of the FPGA has been swapped around). 

 

The demo that JColvin just linked to is the correct version, and should work properly. The demo itself behaves exactly the same as the nexys4-DDR version.

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Yes, I think the file was accidentally stored in a location that was inaccessible to the public.  I re-uploaded it in a different location though, so you should be able to download it now.

 

Let me know if you have any more questions.

 

Thanks,

JColvin

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So I have followed the instructions exactly and hooked up pin AD11P to a function generator oscillating from 0 to 1 volt at 1 Hz (here's a picture, I grounded all the other pins), yet I am getting no response from the FPGA. Will it make a difference that I just have the regular Nexys 4 not the Nexys 4 DDR? Any other idea what might be going on?

Thanks,

rbharvs

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Thank you both so much for your help. Glad I have the board taking analog input now. One interesting point though: we hook up to the input a function generator outputting a slow (~1Hz) 1Vpp sine wave with a 0.5V offset (so that it's entirely positive). The seven-segment display, however, displays values from 0 to ~0.52V and stays at 0 for an unusually long time (~¼ of the period maybe). Any idea why the seven-segment display isn't behaving? I'm currently trying to parse through the demo code to see if there's an explanation there, but I was also thinking it might be an impedance matching issue.

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Are you connecting the ground of the signal generator to the appropriate negative input? I believe that project uses differential analog inputs, so this is necessary. It definitely seems as if the signal is being clipped, and oscillating around 0 V instead of 0.5 V

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