[sdiy] Function Generator ICs

Scott Gravenhorst music.maker at gte.net
Fri Sep 21 15:51:36 CEST 2007

David Betz <dbetz at xlisper.com> wrote:
>> ... 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:

Which board do you have?  When I went to the page above, the page was blank except
for a title banner.  There was a "products" link, so I clicked that and they show
some 12 or so boards, I couldn't figure out which one you have.  I'd like to know
exactly which FPGA you have so I can compare it's internal features.  BTW, I don't
totally understand the "gate count" thing, I have the "500K gate" Spartan-3E
(XC3S500E), oddly though, in my polysynth design, the ISE says the design represents
1,290,000 "equivalent" gates...  The Spartan-3E Starter Kit has an onboard 12bit 4
channel DAC.

>The board I bought has a 1 million gate capacity (an extra $20).
>I also bought the 12 bit stereo D/A module:
>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.

-- ScottG


-- Scott Gravenhorst
-- GateMan I - Xilinx Spartan-3E Based MIDI Synthesizer
-- PolyDaWG/8 - 8 Voice FPGA Polyphonic MIDI Synthesizer
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- When the going gets tough, the tough use the command line.

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