Using a TV tuner as a high speed ADC

tv tuner

The Bt878 chipset is fairly common on TV tuner cards. The chip has a built in analog to digital converter with a sample rate of 119kHz to 448kHz, well above the standard audio rate of 44kHz. The hardware has to be hacked a little to inject your signal since the chip is usually receiving audio from the turner. With some driver hacking this chip can be pushed to 896000 samples per second. Recent developments make things even easier with ALSA support.

[thanks rockarolla]

Comments

  1. Monk says:

    Sweet, now one ponders the possibilities

    audio analysis is a given, but how about a spectrum analyzer, or even a seismic analyzer

  2. TheBlunderbuss says:

    I’m just glad hackaday didn’t piggy-back off of the phone hack on Engadget.

  3. IMWeasel says:

    What would really kick butt is to use the video ADC instead of audio. That should be good to at least a few megahertz.

  4. Mikael Mannberg says:

    #2, I don’t think the point is to record music at 448000 sps (yet). This is really useful for electronics and as a cheap oscilloscope though!

  5. guest says:

    would this be of any use to convert a digital laptop keyboard signal to analog?

  6. nullsmack says:

    This is somewhat useful for simple gnuradio stuff. There’s actually an effort on the gnuradio list to make the main video adc useable for gnuradio stuff. They’re running into the problem of the video adc dropping data for the duration of the vblank I believe. There are undocumented instructions for the controller that people are looking into though. It’ll be sweet when/if they figure it out or someone releases a cheap software card that doesn’t have the same limitation. Especially since the tuner can on the card could be used just to get the signal you want down to IF, then decode the signal in software. Hello poor man’s usrp!

  7. nullsmack says:

    Why were all the capital letters in my post above changed to lower case? :(

  8. Jimmy says:

    I have wondered that same thing for a good while now

  9. ... says:

    would it be possible to do this hack and use some type of ‘scope software in windows without too much effort?

    It would be decently cool to have a .5khz scope for $10… But even sweeter if we hacked into the video ADC for a scope good to a few MHz… for $10.

    finally a real hack, and one for a device I already have!

  10. guest says:

    would this be of any use to convert a digital laptop keyboard signal to analog?

  11. guest says:

    would this be of any use to convert a digital laptop keyboard signal to analog?

  12. DC says:

    That last graph looked just like the response from an otdr, except that the x-axis was frequency not time…

    Pretty cool hack.

  13. ... says:

    no, this hack is for taking an analog signal and making it digital; not the other way round.

    and in regard to post 11, I ment to say .5mhz, not .5khz

  14. lain says:

    guest / #7,#12,#13… a digital laptop keyboard? did you mean a keyboard as in piano-style musical keyboard, or keyboard as in QWERTY.. either way, no this will not convert that way, it is an ADC, that is, analog->digital converter, what you want is a DAC if you want to turn digital into analog :) hope that helps.

  15. Joel says:

    If it’s a delta-encoded ADC, it’ll have a DAC built in, but it might be difficult to access. Here’s to the oscilloscope project, btw. i’m thinking the anti-caps filter is to stop folks from yelling and make for a less formal atmosphere, but who knows?

  16. Joel says:

    Wait a sec…why can’t you just hack an AM modulator circuit, like the kind used to adapt RCA cables to coax? Why hack the tuner card at all?

  17. Bob says:

    #9, #10 :

    The technical reason why is the presence of “text-transform: lowercase;” for BODY in hackaday’s CSS.

    View the source and you’ll see that the comment text still has the original capitalisation, the CSS just makes your browser lower-case everything.

    If it really bothers you then make a copy of the CSS with that taken out and get your browser to use it :)

  18. Jason spence says:

    Couldn’t you get a USB to SPI interface and, say, one of these ADCs to do cheap high-speed acquisition?

  19. domenech says:

    #14

    the last signal is a partial spectrum of a DSL line.

  20. Erik Jackson says:

    The highest end audio interfaces go up to sample rates as high as 192 khz. However, there’s really not much use for this. It’s just a gimmick, TRUST ME. 96 khz is the best any human can perceive. The highest frequency a person can hear with the best hearing is about 22 khz. The reason CDs are 44.1 is because it needs to fold down frequencies of two occurances of harmonics. The reason that we have even higher sampling rates is to solve the issues of even more, higher frequencies occurring at once time. For an example, 4 French horns. They all have really high frequencies in this respect it would be useful to use a sampling rate of 48, 88.1, or 96, but 192 is not even really preceivable. There’s nothing useful for going any higher… unless you are going to down-sample something a ton.

  21. fart says:

    worked on my prolink card, dont realy notice the sound difference.

  22. stillboy says:

    Actually, erik, I have read different about he reasoning for 44.1k sampling on cds, http://www.cs.columbia.edu/~hgs/audio/44.1.html says that the reason is because it works with both ntsc and pal tv. also the sampling rate is like resolution in a digital image. where did you get the information the 96k is the highest anyone can percive? at high frequencies 22k, 96 is only 4.3 samples per cycle. i dont really know but that seems kinda low.

  23. hamburglar says:

    To the person who said this would be better adapted to an O-Scope…

    True, but you have to remember this could be better utilized in a recording scenario… If your mixer is capable of whatever bitrate, your masters will be at the same level. This allows for future-proof recording. 192kHz is about the best you can do now, but in the future, DIYers will have this rate at their will.

  24. hamburglar says:

    …and to the person who asked about the caps thing…

    hackaday only has caps on their page when they get hacked. you should read more.

  25. hamburglar says:

    erik jackson:
    True, the absolute highest frequency any human can hear is near 30kHz, but who’s to say that mid level frequencies can’t be helped by a higher resolution? I understand the basics of sampling rate and the human ear, but I fail to understand why people write the extended resolution off. If you’ve never heard 192kHz, then how can you say it’s no better? Even though you’ll probably pretend you’re a producer and say you’ve heard it, have you ever given it a real test? Straight from your newfangled soundcard? I didn’t think so. The future is always ahead of us, hence, new technology is as well.

  26. mavrik_stoner says:

    how would you take a tuning card(from a tv) and make it for a usb port.

  27. kid zeus says:

    According to Nyquist theorem the sample frequency used must be a minimum of twice that which the human ear can hear hence the reason that Cd’s are sampled at 44.1 kHz just over twice that of human hearing to allow for implementation of a practical anti-aliasing filter. sampling any higher than that makes the sound ‘smother’ and allows for more accurate reproduction of mid range frequencies, harmonics and the likes.

  28. Mark says:

    How about the oposite? Using a high resolution sound card as a TV card?

  29. setsunank says:

    I am investigating about ways to hack and use TV PC cards or even satellite PC cards as ADC to use applications as win-oscilloscope though breaking the sound card frequency limits as many actual signals to test work at high ranges that you cant work properlly with the sound card range.
    Links or any information would be great.

    BTW: there out are some USB oscilloscope devices at 200MS/s approx though thats the fast and costly way to get it solved.

  30. dabdil says:

    okay a hack for someone here maybe.

    Has anyone thought about putting video onto a cassette using the same mechanisms but changing it to digital instead of analogue etc.

  31. Brent F. says:

    I use this for recording off of low-frequency radio. I stayed up late a few nights writing a command line program to shift a band of signals off the high frequency recording down to a standard audio sample rate, and now can hear radio stations. It’s good that there’s still LORAN-C in my area. I can also hear the sound of the radio station WWVB which is used to set radio controlled clocks.

  32. Sebaj_tobias says:

    Hi!

    I have a pctv pro with bt848 chipset.
    That one (and i think the bt878 also) have a 40Ms/s A/D for video sampling.
    I downloaded a program and source code for it. called vbi view or similar.
    Tomorrow i go and test first time with video imput, after that a 14MHz quartz oscillator.
    Anyone have another program for that?

    Tobias

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 94,593 other followers