Spartan 3e starter kit & Multimedia

I just received my Spartan 3e starter kit and had to share my
frustration...

The huge DRAM and the fast FPGA seem to make this board ideal for video
and sound processing. But.. why on earth does the board come with a
3bit VGA output? We do not live in the 80ies anymore. Adding a couple
of resistors to get 8 or 12bit color resolution would hardly have
changed the BOM. Even a video DAC is not expensive.

Same goes to the audio output. The board has some nice DAC, but they
forgot amplifier and usable output connectors.

In contrast, this is a very nice concept:
http://www.terasic.com/english/fpga_01.htm

It just does not have the right FPGA.

Does anybody have a suggestion how to solve the problem? Unfortunately,
a hirose connector is also something that does not come in 2.54mm
pitch.

"BoroToro" <beiermann@gmail.com> wrote in message 
news:1146955848.154397.42440@i40g2000cwc.googlegroups.com...
>
> I just received my Spartan 3e starter kit and had to share my
> frustration...
>
> The huge DRAM and the fast FPGA seem to make this board ideal for video
> and sound processing. But.. why on earth does the board come with a
> 3bit VGA output? We do not live in the 80ies anymore. Adding a couple
> of resistors to get 8 or 12bit color resolution would hardly have
> changed the BOM. Even a video DAC is not expensive.

Not all that difficult to add on another VGA interface with more bits.
One of these could come in handy:
http://www.winfordeng.com/products/brk15hd.php

4 bits for each colour will give you a handy 4096 colours to choose from.

Red.

In article <1146955848.154397.42440@i40g2000cwc.googlegroups.com>,
BoroToro <beiermann@gmail.com> wrote:

> I just received my Spartan 3e starter kit and had to share my
> frustration...
> 
> The huge DRAM and the fast FPGA seem to make this board ideal for video
> and sound processing. But.. why on earth does the board come with a
> 3bit VGA output? We do not live in the 80ies anymore. Adding a couple
> of resistors to get 8 or 12bit color resolution would hardly have
> changed the BOM. Even a video DAC is not expensive.

It would, however, have used up more IO pins.  I don't know if that was
a consideration, but they do seem to share pins for the devices on the
SPI bus.

Does anyone know if doing PWM on the VGA output pins would cause Bad
Things to happen to a typical monitor?

-- 
David M. Palmer  dmpalmer@email.com (formerly @clark.net, @ematic.com)

David M. Palmer wrote:
> In article <1146955848.154397.42440@i40g2000cwc.googlegroups.com>,
> BoroToro <beiermann@gmail.com> wrote:
> 
> 
>>I just received my Spartan 3e starter kit and had to share my
>>frustration...
>>
>>The huge DRAM and the fast FPGA seem to make this board ideal for video
>>and sound processing. But.. why on earth does the board come with a
>>3bit VGA output? We do not live in the 80ies anymore. Adding a couple
>>of resistors to get 8 or 12bit color resolution would hardly have
>>changed the BOM. Even a video DAC is not expensive.
> 
> 
> It would, however, have used up more IO pins.  I don't know if that was
> a consideration, but they do seem to share pins for the devices on the
> SPI bus.
> 
> Does anyone know if doing PWM on the VGA output pins would cause Bad
> Things to happen to a typical monitor?

It would have to be above the video clock rate, and then it
would depend on the slew symmetry of the video amplifier.

For a LCD monitor, it would be more unpredictable, as they sample the
analog IP to create the digital drive signals.

-jg

David M. Palmer (dmpalmer@email.com) wrote:
: In article <1146955848.154397.42440@i40g2000cwc.googlegroups.com>,
: BoroToro <beiermann@gmail.com> wrote:

: > I just received my Spartan 3e starter kit and had to share my
: > frustration...
: > 

<s nip >

: Does anyone know if doing PWM on the VGA output pins would cause Bad
: Things to happen to a typical monitor?


I tried it with the Spartan 3 kit from Xilinx/Digilent a while back and
had some success with PWM - if you count success to mean working on 1 of
4 CRTs tested...   And working being used in a foregiving sense :-)

cds

The problem with PWM here is that there is no filter on the output, so
you get essentially an AC signal that will look pretty rough to a
monitor expecting a DC signal. To get a true DC value out of that, you
need some capacitance. It is possible that if you created a small
adapter with three low-pass R-C filters for each signal, you might get
acceptable results - even on an LCD.

Alternately, you might be able to solder some capacitors directly to
the connector and solder the negative terminals to ground. This depends
on the resistance of the board traces - which may or may not be
adequate.

In article <1147142273.761777.130440@i39g2000cwa.googlegroups.com>,
radarman <jshamlet@gmail.com> wrote:

> The problem with PWM here is that there is no filter on the output, so
> you get essentially an AC signal that will look pretty rough to a
> monitor expecting a DC signal. To get a true DC value out of that, you
> need some capacitance. It is possible that if you created a small
> adapter with three low-pass R-C filters for each signal, you might get
> acceptable results - even on an LCD.
> 
> Alternately, you might be able to solder some capacitors directly to
> the connector and solder the negative terminals to ground. This depends
> on the resistance of the board traces - which may or may not be
> adequate.

There are resistors (few hundred ohms, different for the rgb than for
the syncs) between the FPGA pins and the VGA connector.

But two voices of experience have already chimed in saying that
straight pwm without board mods doesn't work too well.  And if you are
going to do something like solder up capacitors, you may as well just
make your own VGA port with as many bits as you want.

-- 
David M. Palmer  dmpalmer@email.com (formerly @clark.net, @ematic.com)

Perhaps - but three SMT capacitors, a bit of wire, and perhaps a bit of
glue is a lot cheaper than rolling your own PWB. This would be a very
simple board mod that almost any beginner could successfully manage,
and it would be very effective. Cripes - I'm no expert at soldering,
but even I've managed to modify boards in this way.

Also, consider that this allows you to keep all your GPIO (which is
rather limited on the S3E starter kit). If you are successful, you can
still use the  hirose connector for something else (like a video
capture board)

Lastly, not everyone can afford to roll their own PWB's with a true VGA
DAC and connector. My wife would beat me silly if I even contemplated
such a thing. So, if I had the board myself, it would either be roll
the filters on the board, or live with 3-bit color.

> > The huge DRAM and the fast FPGA seem to make this board ideal for video
> > and sound processing. But.. why on earth does the board come with a
> > 3bit VGA output? We do not live in the 80ies anymore. Adding a couple
> > of resistors to get 8 or 12bit color resolution would hardly have
> > changed the BOM. Even a video DAC is not expensive.
>
> It would, however, have used up more IO pins.  I don't know if that was
> a consideration, but they do seem to share pins for the devices on the
> SPI bus.
>
> Does anyone know if doing PWM on the VGA output pins would cause Bad
> Things to happen to a typical monitor?

In some ways this is very similar to dithering. I already used ordered
dithering to improve the color resolution from 8 to 14bit on another
board. Unfortunately 3bit color resolution is extremely low to start
with.

One way out could be to use a PAL/NTSC encoder. Is there any free core
out there?

In article <1147180734.384416.112730@v46g2000cwv.googlegroups.com>,
radarman <jshamlet@gmail.com> wrote:

> Perhaps - but three SMT capacitors, a bit of wire, and perhaps a bit of
> glue is a lot cheaper than rolling your own PWB. This would be a very
> simple board mod that almost any beginner could successfully manage,
> and it would be very effective. Cripes - I'm no expert at soldering,
> but even I've managed to modify boards in this way.
> 
> Also, consider that this allows you to keep all your GPIO (which is
> rather limited on the S3E starter kit). If you are successful, you can
> still use the  hirose connector for something else (like a video
> capture board)

If you are willing to use up the Hirose port, you could probably kludge
up some R/2R ADCs with the resistors hanging out into free space off
the pins of a through-hole connector, with no component more than one
component away from a connector pin.  Not exactly robust, or sound
engineering practice, but usable enough.  And not much worse than what
I was thinking of, which was a clump of capacitors plugged into the
board's VGA socket and leading to a VGA socket to plug your monitor
into.

But it does use up most of your expansion capability.  Does anyone make
a prototyping board with the Hirose connector?  Digilent has some for
the pair of 2x20 pin headers on their boards, but not for this new
board.

But the SMT capacitors solidly attached to the board probably would be
a better way to go.

Another idea, and I don't know if this is possible.  When you set up
the constraint file, you indicate what strength each pin gets driven
at, and what logic family it simulates.  So could you have e.g. a 1.5 V
logic at 2 mA for dim and 3.3 V driving 15 mA for bright?  Or are the
bits that control that not accessible to the logic signals?  Or is it
otherwise a Bad Idea?

-- 
David M. Palmer  dmpalmer@email.com (formerly @clark.net, @ematic.com)