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Microcasting Color TV By Abusing a Wi-Fi Chip (hackaday.com)

Posted by timothy on from the why-does-the-chip-keep-coming-back? dept.

szczys writes: The NTSC standard has effectively been replaced by newer digital standards, but most televisions still work with these signals. This can be done through a composite video connection, but more fun is to broadcast video directly to your television's analog tuner. This is what cnlohr has been working on, using a lowly ESP8266 module to generate and transmit the color TV signal. This board is a $3 Wi-Fi module. But the chip itself has a number of other powerful peripheral features, including I2S and DMA. This hardware makes it possible to push the TV broadcast out using hardware, taking up only about 10% of processor time. Even more impressive, cnlohr didn't want to recompile and flash (which is a relatively slow process) during prototyping so he used a web worker to implement browser-based development through the chip's Wi-Fi connection. Speaking of chip-abuse in the interest of hyperlocal signal propagation, reader fulldecent writes to point out a project on GitHub that "allows transmission of radio signals from a computer that is otherwise air gapped. Right now this could be useful for playing a quick tune or for pranks. But there are more nefarious uses as this could also be used to exfiltrate information from secure networks."

17 of 63 comments (clear)

  1. chip 'abuse' !? by sittingnut · · Score: 2

    'abuse' ?!

    1. Re:chip 'abuse' !? by ArchieBunker · · Score: 2

      Nobody else appears to be using it.

      --
      Only the State obtains its revenue by coercion. - Murray Rothbard
    2. Re:chip 'abuse' !? by BoogieChile · · Score: 2

      > [heavily paraphrased] Running the program on an Apple MacBook Air (13-inch, Early 2015) uses the _mm_stream_si128 instruction to write through to a memory address, causing electromagnetic radiation to be emitted from the computer at 1580 KHz.

      > By tuning an AM radio tuned to this frequency, you should hear "Mary had a Little Lamb" played over and over.

      ...Seems a perfectly cromulent use of the word.

  2. Shades of Don Lancaster's "TV Typewriter"! by jeffb+(2.718) · · Score: 3, Interesting

    This is beautiful. It takes me back to my late teens, building out TTL divider chains and 2K CMOS static RAMs to make a higher-resolution (30 rows of 100 characters) alphanumeric display for the TRS-80. Maybe I won't toss that 1970s 13" color TV just yet...

    1. Re:Shades of Don Lancaster's "TV Typewriter"! by Snotnose · · Score: 2

      Don't forget the games that used white noise to generate a soundtrack. Tune a radio to an unused station, fire up your game, and voila! Sound!

  3. Outstanding! by CaptainLard · · Score: 5, Insightful

    This is the coolest little hack I've seen on /. since...probably dice bought it. More of this please!

    One minor quibble, no need to editorialize the "POTENTIAL SECURITY VULNERABILITY". We already know everything is a weapon for terrorists these days. How about instead of "speaking of chip abuse" we have "speaking of $3 computers with tons of hidden functionality"?

    1. Re:Outstanding! by sunderland56 · · Score: 4, Informative

      Agreed - cool hack.

      There *should* be a big, huge warning, though - about violating FCC rules. The hack broadcasts on restricted frequencies; replicate at your own risk.

    2. Re:Outstanding! by Obfuscant · · Score: 5, Informative

      your car's starter motor violates FCC rules when the brushes get old, so you too will join the others in the gulag for violating the rules

      The phrase "intentional radiator" has a significance here. Google it if you are confused.

      It would be a good question to research if this intentional radiator met the limits of a Part 15 device, like the unlicensed AM and FM broadcast transmitters that you can buy or build.

    3. Re:Outstanding! by ArchieBunker · · Score: 2

      The FCC doesn't care anymore. You have to be interfering with commercial stations for months before they do any investigating. I still hear people talking on the CB with illegal amplifiers. Even if they do fine you, you can appeal it down to a fraction of what they asked.

      --
      Only the State obtains its revenue by coercion. - Murray Rothbard
    4. Re:Outstanding! by tlhIngan · · Score: 2

      Same as taking an FM transmitter meant for linking to a personal vehicle stereo and hooking the antenna to an amplifier.

      Actually, no. The FCC has excluded low-power FM transmitters from requiring licensing, thus making those little FM transmitters for your car perfectly legal. The FCC basically limits their power to 200 feet or less range (the FCC measures output not by mW, but by complete system, so if you have a 200W transmitter with a piss-poor antenna that gives you 200 feet max, that works. Same goes for a 10mW transmitter with efficient antenna).

      XM Sirius Radio (back when it was XM Radio) got in trouble because their FM transmitters were way more powerful than that.

      But no, FM transmitters have an exception as long as it's limited range. The transmitters still need FCC certification as they are intentional radiators, but license to operate and broadcast on the AM/FM band is not required for low-power FM.

    5. Re:Outstanding! by sunderland56 · · Score: 3, Informative

      It would be a good question to research if this intentional radiator met the limits of a Part 15 device, like the unlicensed AM and FM broadcast transmitters that you can buy or build.

      FCC OET Bulletin No. 63, October 1993:
      With the exception of intermittent and periodic transmissions, and biomedical telemetry devices, Part 15 transmitters are not permitted to operate in the TV broadcast bands.

    6. Re:Outstanding! by Toshito · · Score: 2

      If you're doing it from your mom's basement (like any self respecting slashdoter should) the signal will not be powefull enough to get outside.

      --
      Try it! Library of Babel
    7. Re: Outstanding! by sunderland56 · · Score: 2

      The FCC also explicitly bands the amateur broadcast of music for any purpose

      You are talking about licensed Amateur Radio here, FCC Part 97. That is completely different from unlicensed low power transmissions under Part 15, which have no such restriction. Amateur transmissions are prohibited in the broadcast television frequencies.

      The plug-in dongle to transmit from your iPod to the FM radio in your car, for example - a Part 15 device, and it clearly does allow music.

  4. Check the FCC regulations first by davidwr · · Score: 4, Informative

    If you are relying on Part 15 FCC regulations, be sure to read them first. Using a device in a way not contemplated by the manufacturer can turn your "approved" device into a "home-built transmitter [that is] not for sale" which puts the onus entirely on you to comply with the rules.

    Having said that, if nobody complains, then you almost certainly won't be hearing from the FCC, and even if you were to use a device "as intended" and it caused harmful interference, you are still required to cease using it.

    https://www.fcc.gov/Bureaus/En... has an interesting item on page 7:

    With the exception of intermittent and periodic transmissions, and biomedical telemetry devices, Part 15 transmitters are not permitted to operate in the TV broadcast bands.

    I guess that means if you are only going to transmit "intermittently" or "periodically" then this is fine, but it's probably not okay to use this for your home-security system that runs 24/7.

    Channel 3 is in the 54-70MHz band, which is okay but only at very low power, 100 microvolts/m measured at 3 m away ("quasi-peak").

    It is almost certainly legally safe to use this over low-VHF channels over coax rather than "over the airwaves," and you'll probably get a stronger signal to boot. But it won't be as much fun.

    There may be some opportunity to use this under other parts of the FCC rules, such as part 18 (industrial, scientific, and medical) and, on applicable frequencies, part 97 (amateur radio license-holders only, and only in ham bands, and even then NTSC is not an acceptable "mode" in many bands).

    --
    Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
  5. Okay, that document was very out of date by davidwr · · Score: 2

    Oops, I just got egg on my face. That document is 20 years old. Please consult the current FCC Part 15 regulations, which should be widely available.

    My Google-fu is obviously not working well today.

    --
    Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
  6. Didn't work for us in the late 1970s by swb · · Score: 3, Funny

    I forget why, but we had an RF modulator, possibly to connect some early VHS deck to a TV. We also had a video camera and a giant antenna on the roof of our house, and we thought it would be awesome to make our own local channel 3.

    Try as we might, connecting the RF modulator to the TV antenna did not allow our broadcast to be received by anyone in the neighborhood, denying them the ability to see me lipsync AC/DC with a tennis racket for a guitar.

  7. Check out his youtube channel by bangular · · Score: 2

    I stumbled across his youtube channel awhile back looking for info on etching pcbs. He has a few interesting projects going on. https://www.youtube.com/channe...