audio input on nexus 4 dir

[John Martin]

For a school project using the Nexys 4 DDR I need to input audio from a single ended source (voltage+ground).  This can be either directly from a guitar (1Vp-p) or the headphone output of a iPod Nano (2Vp-p).  The Nexys 4 reference does not indicate how the Artix-7 JXADC differential inputs are configured, whether unipolar or bipolar mode.  From the Xilinx doc "7 Series FPGAs and Zynq-7000 All programmable SoC XADC Dual 12-Bit 1 MSPS Analog-to-Digital Converter" it appears bipolar would be needed with the analog source voltage connected to a ADnP and the ground connected to ADnN.  The desired output is 12-bit signed as either audio source is a 0DC with positive and negative values.

Can I do this with the CON4 PMOD connected directly to one of the Nexus 4 DDR PMOD ports or must I use a AD1/AD2 PMOD (with a CON4 PMOD connected to the AD1/AD2 input)?

 

[D@n]

@John Martin,

First, I'm not a Digilent employee.  Nothing I say therefore can come with any manufacturer warrantee, either express or implied. 

That said, after looking over the schematics and the Nexys4 DDR reference manual, it sure looks like that should work.  Be sure you keep your voltages below 3v peak-to-peak and ... let me know how it works.

Dan

[jpeyron]

Hi @John Martin,

To add to @D@n's comment.  I would also look at the tutorial for the Looper demo here and project here. They did not use the PmodCON4 with the  PmodAD1 or AD2. After talking to the creator of the Looper project their only suggestion was that if you use the audio from a guitar run it through an amplifier first otherwise the signal will be very weak.

cheers,

Jon

[John Martin]

30 minutes ago, jpeyron said:

Hi @John Martin,

To add to @D@n's comment.  I would also look at the tutorial for the Looper demo here and project here. They did not use the PmodCON4 with the  PmodAD1 or AD2. After talking to the creator of the Looper project their only suggestion was that if you use the audio from a guitar run it through an amplifier first otherwise the signal will be very weak.

 

The looper project says:

1.2) The XADC requires an input wave biased at .5V, ....

in particular they used AD3P and AD3N.  Their added circuit provides a 0.5V DC bias which I assume presents the 0.5/-0.5V waveforms from the guitar as 1.0/0.0V to AD3P.  Are any of the Artix-7 ADC inputs configured to allow direct sampling of waveforms with 0V DC bias?

[jpeyron]

Hi @John Martin,

Unfortunately, I am not seeing anything that has a 0V DC bais with the XADC so your solution of using the PmodCON4 and the PmodAD1/PmodAD2 would be appropriate. Make sure to follow @D@n warning about keeping your voltages below 3v peak-to-peak.

thank you,

Jon