[sdiy] Function Generator ICs

[David Betz]

> ... the development board I have (Xilinx Spartan-3E Starter Kit)  
> and that the price
> was $149 with lots of goodies (RAM, flash, LCD, rotary encoder,  
> DAC, ADC, etc.) on the board as
> well as a reasonably large FPGA.  Bang for the buck, it's great.   
> It's not an audio board - it's
> a dev board.  It has a 12 bit DAC which works, but is a tad noisy  
> due to a nonoptimal reference
> circuit.  This can be fixed by adding your own DAC through a  
> connector.  The on board DAC has
> been good enough to get things done.  I do MIDI stuff, so I use  
> only the DAC, not the ADC.  For
> MIDI, you need an optoisolator and for the output you need a  
> resistor and a cap.  So you don't
> have to build very much to get started.  The only thing I'd really  
> like to add is a 16 bit SPI DAC.
>

I have been doing something similar (although not nearly as far  
along) using the Digilent Nexys board:

http://www.digilentinc.com/Products/Detail.cfm? 
Nav1=Products&Nav2=Programmable&Prod=NEXYS

The board I bought has a 1 million gate capacity (an extra $20).

I also bought the 12 bit stereo D/A module:

https://www.digilentinc.com/Products/Detail.cfm?Prod=PMOD- 
DA2&Nav1=Products&Nav2=Peripheral

For a total of $140, that gives me most of what Scott has but lots  
more gates to play with. A nice feature of the Nexys board is that it  
uses a USB connection to your PC to get its power as an option. When  
the USB is connected, you can use a fairly simple to implement  
protocol to read/write registers in your logic on the FPGA. It uses  
the same Xilinx tools that Scott's board uses. Unfortunately, it  
doesn't have the rotary encoder.