Turning a Parallax P2 Microcontroller Into a Digital TV Transmitter — The Hard Way

Pseudonymous maker "Real Solar Cars," hereafter simply "Cars," is looking to give future projects a TV output inspired by classic home microcomputers of the 1980s — but modernized, by generating a viewable digital TV signal from a humble microcontroller.

"Some home computers used to have RF [radio-frequency] video output," Cars explains of the inspiration behind the project, referring to classic machines like the Commodore 64 which could be hooked up to the antenna input of any household TV. "The [Parallax] P2 could bring that back with ATSC HDTV output."

Traditional microcomputers making use of their owners' existing TV sets did so by encoding the video signals as analog RF signals — the same signals you'd pick up with your "bunny ears" antenna back in the day, but wired straight into the TV's analog tuner via co-axial cable. Modern TVs lack an analog tuner, but many come with a digital tuner in its place — and it's this tuner Cars is targeting with their work-in-progress project.

"The Parallax P2 is a very powerful microcontroller, capable of generating 1080p component and VGA video," Cars explains. "Unfortunately component and VGA inputs are disappearing from new monitors. The P2 can generate HDMI but maximum of about 330Mbps falls short of the 750Mbps needed for 1080i.

"If we could generate an ATSC [Advanced Television Systems Committee] signal we could feed that into the [digital] RF input on all TVs," Cars continues. "Then we could use the TV's MPEG decoder as a graphics accelerator. The 4MB required to buffer a full frame full color image would be stored in the TV memory. A big benefit on a microcontroller with 512kB RAM. Scrolling could be done with motion vectors."

Traditionally, a digital TV signal is generated by a dedicated encoder — but Cars is looking to do it the hard way, using nothing that isn't already aboard the Parallax P2. So far, he's achieved an impressive proof-of-concept: a valid but unfiltered ATSC signal that s picked up and decoded correctly, looping a few seconds of video loaded from RAM.

There's a trick to it, of course: the ATSC stream itself was generated off-device using GNU Radio and saved to a microSD card, then loaded in to RAM to improve performance. The next step: finding a way to generate everything on the microcontroller itself, which could prove a challenge even with the Parallax P2 overclocked to 300MHz from its stock 180MHz.

Interested parties can follow Cars' progress on Hackaday.io.