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Hardware Hacking Television Wireless Networking Build

Microcasting Color TV By Abusing a Wi-Fi Chip (hackaday.com) 63

szczys writes: The NTSC standard has effectively been replaced by newer digital standards, but most televisions still work with these signals.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."
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Microcasting Color TV By Abusing a Wi-Fi Chip

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    • by Anonymous Coward

      "ab-use" to use something in a manner not originally intended

      overclocking the I2S fifo to the megahertz range is clearly "ab-use" unless you have some sort of miracle eardrum that can vibrate at that frequency

      • by sjames ( 1099 )

        Actually, abuse explicitly includes that the use is bad or harmful.

        If the chip fails in a few minutes of that, it is abuse.

        • Actually, abuse explicitly includes that the use is bad or harmful.

          If the chip fails in a few minutes of that, it is abuse.

          Except for self abuse. Then it's just fun.

          • by sjames ( 1099 )

            Sorry to hear about your failure problem. There are drugs that might help that.

            • Sorry to hear about your failure problem. There are drugs that might help that.

              Now now, A sense of humor, so lacking in many these days, is a great help in getting through life happily. And alas, there are no drugs for that.

              Well, maybe Nitrous oxide.

    • Well, it's spectrum abuse at least. You're explicitly not supposed to be using that spectrum for this shit.

    • > [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.

  • by jeffb (2.718) ( 1189693 ) on Tuesday March 01, 2016 @02:45PM (#51616733)

    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...

    • 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!
  • Outstanding! (Score:5, Insightful)

    by CaptainLard ( 1902452 ) on Tuesday March 01, 2016 @02:47PM (#51616755)

    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"?

    • Re:Outstanding! (Score:5, Informative)

      by sunderland56 ( 621843 ) on Tuesday March 01, 2016 @02:53PM (#51616799)

      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.

      • by SeaFox ( 739806 )

        The hack broadcasts on restricted frequencies; replicate at your own risk.

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

        • by tlhIngan ( 30335 )

          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 f

      • by Toshito ( 452851 )

        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.

    • 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... [youtube.com]
    • by I4ko ( 695382 )
      Well it is nice, but it is late. 11 years ago we (one person at least) knew how to transmit both analog and Digital, yes digital with a homebuilt equipment [bellard.org] [bellard.org]
  • by davidwr ( 791652 ) on Tuesday March 01, 2016 @02:58PM (#51616827) Homepage Journal

    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... [fcc.gov] 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).

    • 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.

      • You can tell the slashdot crowd has matured when it starts to look up the rules pertaining to something when a hack is posted. While it may be for the better, I like the days when we could push the bounds without question. I don't think the new kids these days are pushing the limits anymore.

        Whatever happened to pirate radio?

        • I don't think the new kids these days are pushing the limits anymore.

          Whatever happened to pirate radio?

          They put Kevin Mitnick in jail for 5 years for hacking the phone system.

  • by Anonymous Coward

    but doesn't radio transmission implicitly imply that the devices are air gapped....

    oh well, anything to keep the sheeple busy running around and wondering. Better than them coming after you and tearing you a new one.

    good grief.

    • by bws111 ( 1216812 )

      Wifi uses (wait for it) radio transmission. You would have to be a complete moron to consider a device with active WiFi to be 'air gapped'. Even more shocking (to you) is the fact that even wired devices can also have radios!

      The remainder of your post appears to have been written by a random word generator.

    • The term "radio transmission" is sometimes loosely used to mean "radio frequency transmission" which can mean over a coax or other wire carrying the signal rather than as photons through the air (or free space or water or what-not).

      The Hack-a-day link specifically mentioned non-over-the-air applications using TV ("RF") frequencies.

  • by swb ( 14022 ) on Tuesday March 01, 2016 @03:28PM (#51617055)

    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.

    • You didn't have enough power. I mean, most of those RF modulators didn't even have external power sources, and were only designed to work through a few feet of coax.

      If you'd tried to hack one of those Rabbit cable TV/VCR signal extenders instead, it at least would have been designed to transmit over air and maybe you would have had enough power to do something.

      • by Anonymous Coward

        Here's the formula for easy NTSC broadcasting on Channel 3:
        1. NTSC device (VCR, camera, etc.) outputting via composite or S-Video and RCA R-L audio
        2. RF Modulator with output via RG-59 or RG-6 coax cable
        3. Channel Master or Winegard VHF-LO preamplifier with lots of gain
        4. Matching transformer ("balun") for converting 75 coax unbalanced to 300 twinlead balanced signal
        5. DIY dipole antenna with end-to-end width of 2.38095m (93.74in) and attachment points for balun leads
        6. connect device to modulator to preamp

    • Maybe the range was too far? I found I could use my 8 bitter to drive the TV across the room by connecting a TV antenna up to its RF out port. That was only a few meters though.

  • Right now, I think the cheapest ATSC "modulator" (probably not the right term) is in the neighborhood of $1000. Would be nice to connect something like this to in-home wiring to stream video over existing wiring.

    • by rrp ( 537287 )
      There are some GNU Radio scripts that will let you broadcast ATSC with a Software Defined Radio (SDR), like the HackRF. Not sure how well they work, as I don't have a SDR, but I've been wanting to get one to try it out.

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