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RF video connection to HDTV (ATSC) — Parallax Forums

RF video connection to HDTV (ATSC)

So the P2 can emit an ATSC HDTV signal.* https://hackaday.io/project/194559-atsc-transmitter-from-parallax-p2-microcontroller Is this something people would be interested in?

The good:

Transmit a solid 19.3 mbps over a coaxial cable and receive it with a standard HDTV tuner stick.

Display up to 1080i resolution. Maybe newer TVs would even accept 4k.

The P2 Edge with 32MB ram can play a 6 second video loop. That could be lengthened by doing more of the signal processing on the P2. The ATSC standard is not very computationally intensive to transmit.

The bad:

The P2 doesn't read the 19.3 mpbs from SD card needed for a proper video player. But how useful would a video player be?

I think it would be possible to make a heavily modified MPEG encoder that uses text as an input instead of video frames. What is the obvious way to do this? Look up a bitmapped font for the character. Then assemble an image of the text. Feed that to an MPEG encoder. The encoder will do a discrete cosine transform, quantization, and Huffman coding. Now if we put some restrictions on the size of the font we could speed up the process a lot. Suppose we used the character and looked up a pre-computed image block. Hopefully at the Huffman encoding stage. So maybe we could build a 1080i MPEG stream of text by simply concatenating data from a table. That sounds like a lot of work to me.

There might be too much lag from the TV's MPEG decoder for a fun computing experience. It will be hard to know without testing.

On most TVs it seems necessary to rescan for channels when switching from the P2 to broadcast TV and vice versa. This could be remedied with a diplexer. Most HDTV signals are UHF. The P2 is best suited for VHF low signals. The diplexer would allow both the P2 signal and local TV stations to be available to the TV at the same time.

The P2 probably can't do OFDM based signals like DVB-T. That requires less than 280uS for a 2048 IFFT or 1120uS for a 8192 IFFT. P2 needs 1185uS for 2048 FFT and 5674uS for a 8192 FFT at 320MHz. So maybe DVB-T would be doable if we had 5 or 6 cogs just for the IFFTs.

. * Of horrifying spectral purity. Although the Raspberry Pi FM transmitter used to be worse.

Comments

  • evanhevanh Posts: 15,043

    Is that a reason to get a full SD 4-bit mode working? It won't be able to use the built-in 1-bit SD slot on existing boards.

  • cgraceycgracey Posts: 14,112

    Yeah, that would be cool!!!

  • RaymanRayman Posts: 13,711

    Did they actually produce an image on a HDTV over coax cable this way?
    Can't really tell from that website...

    Text mode might be interesting. My understanding is that mpeg divides the screen into 16x16 pixel areas for coding/decoding. If you had a 16x16 pixel based font, maybe that could be pre-encoded and sent easily?

  • ke4pjwke4pjw Posts: 1,048

    Why can't the P2 read 2MB/s from SD? I would think it can, but have never tested it.

  • ke4pjwke4pjw Posts: 1,048

    Also, this is a very cool idea! That's a "one wire" video solution, LOL.

  • pik33pik33 Posts: 2,342

    @ke4pjw said:
    Why can't the P2 read 2MB/s from SD? I would think it can, but have never tested it.

    It can, at least using Flexprop's drivers. The available speed is over 3 MB/s

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