Lab 5 - DAC Siren

Introduction:

In this lab, we will program the FPGA on the Nexys2 board to generate a wailing audio siren using a digital to analog converter (DAC). This will require us to format our digital audio sequence into a serial stream that can be used to drive an outboard DAC.

Steps:

DAC Interface :

• We will be using a 16-bit stereo Digital to Analog Converter module PmodI2 S which plugs into one of the PMOD connectors on the Nexys2 board. The module and its connections are shown in Figure 1
• The DAC converts “left” and “right” 16-bit digital data streams into two analog left and right channel signals which can be used to drive a stereo speaker system
• The DAC employs an oversampled Delta-Sigma Modulator to convert the digital data into analog format

Hardware Setup :

• Plug the PmodI2 S module into PMOD jack JA on the Nexys4 board (Figure 2)
• Plug the module into the top row of sockets on JA

Configure FPGA :

1. Using the same project settings from the previous labs, create a new project titled 'Siren'.
   • Shown in Initial Project Setup in Lab 3
2. Create a new source titled 'dac_if'
   • Shown in Initial Project Setup in Lab 3
   • Code found in Figure 3
3. Create another source titled 'tone'
   • Code found in Figure 4
4. Create another source titled 'wail'
   • Code found in Figure 5
5. Create a top level source titled 'siren'
   • Code found in Figure 6
   • This is the top level that hooks it all together. In this module:
     • The constants lo_tone, hi_tone and wail_speed define the parameters of the siren
     • The 20-bit timing counter tcount is used to generate all the necessary timing signals
     • The module wail is instanced to generate the 16-bit signed audio sequences data_L and data_R
     • These sequences are then sent to an instance of dac_if to convert them to the required serial stream
     • Primary outputs of this top level module go directly to the DAC
6. Add an Implementation Constraint source file titled 'siren'
   • Code found in Figure 7
7. Highlight the 'siren.vhd' module in the Hierarchy window and run Synthesis
8. Run Implementation
9. Generate Bitstream
10. Plug in the device if it is not already and Vivado should detect the board
11. Click Program Device and load the generated bitstream onto the board
    • If you cannot click Program Device, click Open Target first
12. Plug the DAC Module into either a speaker or headphones.

If everything was correctly setup, you should be hearing a siren, similar to the siren sound on a police car.

Helpful Resources:

How to set up the bitstream:

http://users.wpi.edu/~rjduck/Nexys4DDR%20Vivado%20VHDL%20Decoder%20Tutorial.pdf

How to Connect The Nexys A7 to your computer:

https://github.com/Digilent/Nexys-A7-100T-GPIO

Dr. Ackland's Lab Manual:

http://personal.stevens.edu/~backland/Courses/Course487_Spring_18_files/Labs/Lab5.pdf

GitHub:

https://github.com/kevinwlu/dsd