8-bit Computer TV Channel Use

[Alan Hightower]

On 2015-06-01 20:24, Mark J. Blair wrote: 

> I'm also working on getting design details from Silicon Labs for one of their inexpensive single-chip TV tuners under NDA. If the Crazy Cat Lady project moves forward, that chip might come in handy. If I use that chip, I'll need to consider whether the NDA terms would preclude me from sharing my own IP that uses the chip, since I'd prefer to share my schematic and firmware. But if the NDA would disallow that, then I'd either need to close part or all of my design, or pick out a different tuner option.

As far as the crazy cat lady project, as I was trying to explain
earlier.. my $.02 which maybe redundant to your own thoughts: 

VIDEO ADC/DECODER 

You can certainly use an off-the-shelf part as there are 47 from 5
companies on Digikey alone in solder friendly packages. However if the
classic machines you are targetting are producing a clean conforming
NTSC_M/J, PAL_B/G/N, or SECAM signals, stock video decoders on most
converter boxes would work perfectly already. I doubt you will have much
luck with the NDA process explaining a hobby cause but worth a try. Even
if you are successful, make sure the parts you are looking at are
readily available in 10s and 20s quantity through a distributor chain at
a reasonable cost. That may be a second hurdle if it's fairly exotic.
What SiLabs part are you looking at? I can't find any recent video
decoder offerings. 

GENERIC ADC/DSP ANALYSIS 

This is the harder path to go down. You will need a symbol rate of at
least 54 Mhz from a single or two interleaved ADCs to have a shot at at
least 50% phase accuracy (NTSC = 13.5 MHz). There are some relatively
inexpensive options, but I suggest getting a lot of input from folks and
other reference designs on the best way to build an analog front-end for
composite. And only do composite/S-Video. There are already commodity
solutions for stepping down broadcast RF frequencies to base-band. After
that, you will need something fairly hefty at the start to find the
characteristics of the signal and align the sampling. Then you just need
to track clock drift and adjust a VCXO. Straight-forward in hardware,
but I doubt many people will have the experience to add new software
support for <insert eclectic hardware platform with slightly
non-standard composite output here> and fix bugs when they occur. So set
expectations on your time early with respect to project support. 

SOC/ZYNQ/MARKET 

The fact you mention ZynQ throws up a few warning flags for me. It's
probably overkill, it's expensive in low quantities through normal
distributors, and it's not very hobby friendly. $65 for a '010 alone +
DDR3 + BGA assembly would drive the resulting cost for you to make these
boards well beyond $200. And your market is small - vintage computing
folks w/o a CRT on a limited budget. Considering that, you probably
should not try to build the processing core yourself. Run the ADC output
or the video decoder Bt.656 output into a stock board like a Parallella,
BeagleBone Black, or other EVM that has the processing power, HDMI
output, and input interfaces you need; especially to start with. Then go
full custom later. 

-Alan