Re: [Discuss-gnuradio] Status of BTTV/CX88 capture

[Martin Dvh]

Hi Hew How Chee,
> I did some experiment on the CX tv card some time
> back. Looks like a continuous capture of 28MHz 8 bit
> data from the video ADC is possible, at least it seems
> like that.
This sounds very promising.

> I tried capturing  a sine wave and also raw
> composite TV signal. However I did not proceed further
> because the data looks noisy, even with no input. Not
> sure whether is it cause by the  PCB layout. 
I know the bt878 changes the ADC reflevel down when it sees no or only small 
signals. This way it tries to keep a constant signal level.
(A kind of AGC), The cx23888 does probably a similar thing.
When you input no signal, the ADC goes automatically to its highest sensitivity 
so you get a very high noise level.
This should go away if you input a big enough signal.
Normal videosignal is 1volt peak to peak (video black is 0 V, video white is 
0.7 V, sync tip is -0.3 V)

The quality of the signal will of-course not be the same as with an usrp but with my bt878 card I had low enough noise to receive broadcast FM, 
narrowband fm (police) and narrow-band am (air-traffic)
As frontend I used the IF of the tuner which was on the capture card (added an 
IF output myself)
> The sine
> wave signal came from Palm since I dont have a sig
> gen. As for the video signal, it came from videocam.
You could also try to use the soundcard output of your pc as a signal generator.
(using gnuradio or audacity)
The videosignal is AC-coupled followed by a DC-restoration circuit (using sync 
and blacklevel for this)
Lowest frequency it should at least let through is 50 Hz (probably lower)

If you capture the signal from the videocam it is also possible to see if you 
have continuous capturing.
If the videosignal and all sync information is in the output then you really 
have continuous capturing.

> I deleted the capture data when I reformat the hard
> disk. If anyone is interested to look at it. I can
> recapture the data this weekend, hopefully I can dig
> out the source code.
I would be very interested in the source-code and the capture data.
How did you put the card in continuous capture mode?
And do you remember if it missed no samples (look at more data then one field 
(20 msec))

Greetings,
Martin
> Regards,
> HowChee
>
>
>
> --- Martin Dvh <address@hidden> wrote:
>
>
> > Cory Papenfuss wrote:
> >
> > >    Just wondering if there's been any more
> >
> > progress on that front.  A 
> >
> > > recall awhile back some promising information on
> >
> > continuous raw captures 
> >
> > > on CX88-based cards.  It would definately be an
> >
> > inexpensive way to play.
> > I haven't been working on this lately.
> > I still don't own a capture card with this chip.
> > I did hack the cx3288 driver and others tried this
> > out.
> > Enabling the RAW_ALL bit didn't result in a
> > continuous capture (yet).
> >
> > Since there are a lot of (undocumented) registers of
> > which the values are very interrelated hacking a
> > driver when others have to test every 
> > change goes very slow.
> >
> > Of course, buying one of these for myself would
> > increase the development speed but since the outcome
> > might very possibly be that it cannot be 
> > done I did'nt do that.
> >
> > If anybody who has a capture card with this chip
> > wants to go ahead and try hacking the driver further
> > I would be more then willing to help.
> > (My code so-far is at
>
> http://www.olifantasia.com/pub/projects/gnuradio/mdvh/cx2388x/
>
> http://www.olifantasia.com/pub/projects/gnuradio/mdvh/bt8x8_driver/
>
> http://www.olifantasia.com/pub/projects/gnuradio/mdvh/examples/
>
> http://www.olifantasia.com/pub/projects/gnuradio/doc/specsheets/
>
> > )
> >
> > Also look in the gnuradio mailing list archives for
> > [Discuss-gnuradio] using ADC of a TV-card with
> > CX2388x chip or digital TV-reception chips/cards
> > [Discuss-gnuradio] ATTN Martin Dvh: cx8800 driver
> >
> > Since recently, I own an usrp.
> > I am still interested in using a hacked tv-card
> > since my experiments with the hacked bttv card
> > delivered  60 Msamples/sec to main memory without 
> > problem.
> > With the usrp I am limited to the usb2 bandwidth
> > (which restricts me to 4 Msamples/sec on my pc which
> > has a cheap usb2 pci add-on card).
> >
> >
> > greetings,
> > Martin
> >
> >
> > _______________________________________________
> > Discuss-gnuradio mailing list
> > address@hidden
>
> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
>
>
> __________________________________________________
> Do You Yahoo!?
> Tired of spam?  Yahoo! Mail has the best spam protection around 
> http://mail.yahoo.com 
>
>
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio