[sdiy] New digital audio SDIY project

[Eric Brombaugh]

Thanks Csaba,

Two boards with shipping and setup from BatchPCB cost about $80. I  
haven't done an exact accounting of parts costs, but in single/small  
qty the main ICs on the board should total about $45, while the  
remaining passives & connectors will probably be about $20-$30. Off- 
board parts (LCD, power supply, cables & connectors) as well as the  
micro SD flash memory aren't factored in.

This project required a few new techniques for me. Probably the  
biggest departure from previous assembly skills was using the hot- 
plate reflow process necessary for the dual LDO with heat-slug and the  
micro SD socket. It worked out pretty well on the first try though,  
and that was with without using a stencil - just applying solder paste  
with a toothpick & scalpel and cleaning up edges with a cotton swab.

There were a few unknowns in this design as well. I wanted to  
experiment with the feasibility of using a 2-layer board for an system  
with an FPGA. All the manufacturers documentation has dire warnings  
about layout approaches required for safely using their parts, almost  
all of which involve complex routing & decoupling schemes that seem to  
require 4 layers at minimum.  I was able to route the 3 supplies and  
decouple each of the 16 power pins on the VQ100 package, and the FPGA  
came up without any problems in the circuit.

Another question was power supply requirements - most of the FPGA  
development boards out there use multiple switching supplies due to  
the potentially heavy current demands of these parts. The FPGA  
manufacturers can't predict the nature of the designs you'll load into  
them, so the power supply specs are pretty vague too - they give  
minimum quiescent requirements, but the upper end is fairly nebulous.  
Fortunately, I found a dual linear LDO specifically designed for high- 
current digital parts that was pretty simple to use. So far my trial  
design hasn't taxed the power available, and the regulators barely get  
warm.

Lots to learn...

Eric

On Feb 28, 2009, at 3:52 AM, Csaba Zvekan wrote:

> Awesome project , Eric. Congratulations you did it again. I guess  
> you really like making these boards.
> You know I will most likely build one for myself. As I just love  
> solder SMD parts by hand.:)
>
> How much was the board cost with BatchPCB (I assume you did it  
> there ) ?
> And parts like FPGA,ARM, CODEC and the small stuff ? So I know  
> aproximately how much to expect .
>
> Keep us posted of your process
> Thanks
>
>
> Csaba
>
>
> ----- Original Message ----- From: "Eric Brombaugh" <ebrombaugh1 at cox.net 
> >
> To: "sdiy" <synth-diy at dropmix.xs4all.nl>
> Sent: Friday, February 27, 2009 5:01 PM
> Subject: Re: [sdiy] New digital audio SDIY project
>
>
>> Dial the way-back machine to about a month ago when I announced  
>> this project. I have the boards back from fab and I've built one up  
>> and debugged the initial bootloader & firmware. So far everything  
>> is working as expected. I've updated the web page with photos for  
>> the curious and firmware for anyone who wants a challenge.
>>
>> Now to do some synthy stuff with it!
>>
>> Eric
>>
>> Eric Brombaugh wrote:
>>> Just to muddy the waters a bit. :)
>>>
>>> I've been working on a new digital audio project for the last few  
>>> weeks and we've been discussing it on the FPGA-Synth mail list for  
>>> a few days where I got some useful input from several members. I  
>>> finally sent the PCB design of to fab the other day, so now's the  
>>> time to announce it here:
>>>
>>> http://members.cox.net/ebrombaugh1/synth/armfpga/index.html
>>>
>>> Basic idea is an ARM processor, USB, microSD card slot, MIDI,  
>>> decent-sized FPGA, moderate-sized fast SRAM and 192kHz/24-bit  
>>> codec, along with some useful options for user interface and  
>>> future expansion. Lots more details on the website for the curious.
>>>
>>> I expect to have the prototype on the bench in a month or so.
>>>
>>> Let me know what you think!
>>>
>>> Eric
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy