Re: [Discuss-gnuradio] Cheap ADC at 35MHz

[Adrian Godwin]

> 
> I've been looking at the chip data sheets
> http://www.conexant.com/products/prodsubcat.jsp?id=92 but wasn't sure how
> to gain access to this raw feed.  It looks like you've already taken the
> first steps.

I think only 878 (which newer cards use) is there. There are some other
datasheets cached at
ftp://telepresence.dmem.strath.ac.uk/pub/spec/brooktree/
This is linked from the bttv web page at
http://www.metzlerbros.org/bttv.html

The general idea seems to be to use the vbi facility in full-screen
mode.
There are registers which control how much is captured, but I haven't
tried tweaking them yet.

> According to one of the more complete user review sites, 
> http://www.vcdhelp.com/capturecards.php, two of the most popular frame 
> capture boards with Linux support are Hauppauge WinTV GO 

This is currently at Maplin (www.maplin.co.uk) for 40 UKP. It has 
a cable-ready tuner. They also have an Avermedia TV203 at the same 
price : I'm not sure what device that uses, but earlier versions 
(TV103 etc) did use the Brooktree parts. Both Avermedia and 
Hauppage acknowledge the existence of the Linux drivers.

> BTW, it likely that the simple frame capture boards we want will soon be
> discontinued in favor of more sophisticated versions with build in MPEG
> compression (which do not seem to have a raw mode feature).

Yes. The simple cards have also given way to USB (for webcam capture)
or Firewire (for video editing) so these may become hard to find.
The Bt848 is already obsolete and the 878 is in end-of-life.
The cable-ready tuners will also disappear as analogue cable is
phased out (almost gone in the UK).

However, this is a great time to pick them up cheap : I have 3, all
bought for a few pounds at boot sales. I'll look out for some more.
It might be worth investigating the USB adapters, too : again, the 
Hauppage card advertises high-resolution still-image capture.


Mine are 

  - an Intel Bt848 board. Well laid out, S-Video, phono and camera
    connectors (The camera conector has power and digital in)

  - a Videologic Bt848 board. Fairly decent, with space for a 
    tuner (not fitted), S-video, and audio (simply bridged to the
    sound card).

  - A ModTec MM205 Bt878 card, generic far-eastern manufacture. 
    Nasty quality, but fitted with a tuner (UHF TV band only).
    I never got the sound working on this, even with the Windows
    driver (the Linux driver didn't support the digital sound
    channel at the time I tried it).

Note that quite a lot of these boards are packaged and labelled
as the same thing but actually change maker and components 
quite regularly. But because almost all the hardware is on-chip,
the signals that are accessible on one board will usually be
accessible on another board, too.

-adrian