Comment by andrewstuart | Hacker News Reader

Comment by andrewstuart | Hacker News Reader

Two types of minimal computing - don't get them confused:

There's "pack as much power as you possibly can into a minimal computer" - that's raspberry pi.

There also "drive tiny, minimal CPUs to do amazing things at the edge of their specifications cause it's cool and fun" type minimal computing - that is this device.

People who don't understand the distinction will always say "Huh? Why is this interesting? I don't get it.... a raspberry pi is the same size and more powerful."

If you really want to be knocked out, see how the ESP8266 CPU in this device is able to generate a wireless NTSC video signal with zero extra components https://www.youtube.com/watch?v=SSiRkpgwVKY and then the next level Charles Lohr takes it to color https://www.youtube.com/watch?v=bcez5pcp55w

Put another way, the ESP8266, with nothing more than a wire connected to it, is able to generate a broadcast TV signals and display 3D graphics on that broadcast TV signal.

The ESP8266 was also tested by Charles Lohr to have a wireless CPU to CPU range of 1 kilometer https://www.youtube.com/watch?v=ekSsi83-x8M

I hate when interesting stuff like this is stuck in a video. Fortunately it's only 3 minutes long, and by judicious skipping I found his github: https://github.com/cnlohr/channel3

Short answer: the internal I2S peripheral will let you output at 80MHz (!), which can be used to generate by PWM the NTSC 315.0/88.0 MHz chroma frequency.

"This is basically a 1-bit dithering DAC, operating at a frequency below the nyquist, trying to encode luma and color at the same time. Don't be surprised that the quality's terrible."

I was a bit ho hum at

> is able to generate a wireless NTSC video signal

But then I read

> is able to generate a broadcast TV signals

and I read it again.

Are you telling me this will actually produce a RF signal that could be picked up by a 80s era portable television?

That is indeed amazing and I actually wouldn't have thought it possible with a digital device.

EDIT - Having just watched that video I can say that is truly amazing. That has made me so happy.

When I first saw the video by Charles Lohr (a certified genius IMO) I had to spend several minutes trying to get my head around what he had done.

Using the DAC he bit bangs a signal at just the right frequency to match NTSC channel 3 which gets picked up as a TV/radio signal by the TV and displays it. Charles ensures the bits that generate the radio signal match the requirements of the NTSC spec.

Then he displays 3d graphics over that NTSC broadcast signal. Then he adds NTSC color.

That is software defined broadcast television. Mind. Blown.

I started collecting old TV's being dumped out the front of houses for hard waste collection after I saw that video, so I could give it a try.

And the esp8266 CPU costs about $4

If you liked that then you'll love the work that bitluni is doing with the ESP32 chip - the big brother of the ESP8266

AM Radio Transmitter on ESP32 https://www.youtube.com/watch?v=lRXHd3HNzEo

And then a series of videos in which he turns a $5 ESP32 into a games console with composite video and audio

part 1: esp32 composite video

https://www.youtube.com/watch?v=5t1_XNc3vNw&t=4s

part 2: esp32 composite video PLUS audio

https://www.youtube.com/watch?v=MOoKQnWF4OY&t=2s

part 3: esp32 composite video PLUS audio PLUS color

https://www.youtube.com/watch?v=-JXuwwXQh8c

part 4: writing a console game for it all

https://www.youtube.com/watch?v=ssrotAyU61I&t=2519s

It's not precisely broadcast, it's in the "baseband" region and would require modulation up to RF frequency to actually transmit over a distance.

See earlier work by Fabrice Bellard: https://bellard.org/dvbt/ (arguably more impressive signal processing, but requires a graphics card's high-speed DAC)

> and would require modulation up to RF

Can you elaborate? Seems to me it's working without any additional analogue circuitry ...

No, you're right and I'd got my frequency bands wrong, was thinking of 698-806 MHz. 61.5MHz is the broadcast RF band for channel 3, not the baseband.

(I've probably spent too much time around modern radio systems and just casually assumed that 61MHz was too low to be useful, oops)

30 to 300MHz still has the ITU designation of "very high frequency". I know that these days all the sexy stuff is microwave, but the EM spectrum is useful all the way down to DC. The cave radio system used in the rescue of the Wild Boars operates down at 87 kiloHertz. Surface-to-submarine radio systems all operate below 30kHz.

Slightly related: FM transmitter with literally only 3 components: http://spritesmods.com/?art=avrfmtx&page=2

This is the best, most concise explanation of the key EE trade-offs in this kind of stuff I've read - optimizing around different corners of the performance envelope.

I'm not sure I'd want one of these, but I am happy it exists.

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