Posted by interfeco 3 days ago
Would have been nice to hear how specifically it was made to work in the end.
> Turns out, cross-fading two 4MP images at 60 frames per second on a moderately powerful single board computer is not so easy.
Yeah, at first it feels stupid that every pretty LCD screen for bus or train stops, ads or whatnot has a full computer behind it, but then you ballpark the memory bandwidth and realize you need a ~ 1 GHz device anyway just to be able to chew through the pixels fast enough. (1920² px × 24 bpp × 60 Hz = 620 MB/s.) You also realize why “fill rate” used to be such a buzzword 20 years ago and why it took a while until true color became ubiquitous.
On the flip side of the O(n²), you can easily drive a watch-sized display with pretty good ppi using a 32-bit MCU, which is why the Apple/Google/Samsung battery-guzzling approach to smartwatches seems wrongheaded to me compared to Pebble/Zepp/etc.
And train stop displays certainly don't need 60 fps.
The main constraint for high-resolution displays is memory, not CPU clock speed. Your (odd) 1920x1920x24bpp frame buffer takes up more than 10 MB.
I've finally finished my dream music streamer featuring a vinyl-sleeve-sized square display, a custom carrier PCB for a compute module and a 3D printed case, running a custom-compiled kernel, Alpine mini rootfs and a small C app driving the display.
I did not think that this was doable by a hobbyist at all, let alone using free/open source software only (KiCAD, FreeCAD, VSCode). Turns out I was wrong!
Do you have plans to make the project open source?
How did you learn this?
As a hobbyist I found hardware to be quite impenetrable, given the hard mathematics and physics requirements. My attempts to learn this essentially degenerate to taking an informal engineering course. It quickly becomes clear that I'm years away from making something, and I eventually run out of both free time and executive function. AI's been helping... But I don't have the ability to tell when the output is wrong.
I'd previously had a barebones interest in electronics (think: kits with LEDs and buzzers in like 3rd grade), but listening to his discussions and explanations of how these things worked gave me a fairly decent understanding of how some basic electrical principles work.
I also recently watched a video series[1] that explained how microcontrollers (specifically the ATMega328, the one powering the Arduino) work, from a very low level that I've always wondered about. The key part of that series, for me anyway, was getting the chip off of the Arduino PCB and onto a bare breadboard. From there I went and read/skimmed the ATTiny85 datasheet[2] (a very popular "baby brother" chip to the ATMega328) which also helped me understand how these chips do things like PWM on a low level.
I've built one project (a simple PWM dimmer based on a potentiometer) and am working on another (designing a PCB with KiCAD[3] to replace the circuit board for a battery-powered LED lantern, so I can design my own sequencing interface for what happens when you press the singular button), and it has been quite the learning experience, but one I've greatly enjoyed!
[0] https://www.youtube.com/@bigclivedotcom, also at https://odysee.com/@bigclivedotcom:0d
[1] https://www.youtube.com/watch?v=tBq3sO1Z-7o&list=PLNyfXcjhOA...
[2] https://ww1.microchip.com/downloads/en/devicedoc/atmel-2586-...
[3] This comment is long enough already, but KiCAD is a fantastic piece of FOSS software. It's a full schematic/PCB design suite, and there are plenty of tutorials all across the Internet for it.
IMO there aren't any. It's mostly about reading datasheets, and connecting pins to each other IOC those datasheets.
Maybe the physics and mathematics are more important for analog electronics or designing ASICS?
Do you have any specific projects you'd like to build? Post here and we can talk through it. And/or start by downloading KiCAD and clicking around until you understand the UI.
The programming side is mainly also reading datasheets. Instead of connecting the right pins together, you are writing a certain value to a register, as described in tables.
You can learn something practical like "embedded DisplayPort should be impedance controlled to 100 Ohms" without fully understanding the physics behind it.
AI can be very convincing. It told me to put the ESD protection as close the Ethernet connector as possible, so I put it between the port and the magnetics. This worked, but resulted in around 1% packet loss. When I moved it after the magnetics, I got 0% packet loss. This cost me a full revision, but I'd say this is the price to pay for not learning everything by the book.
For GP: this is something you would learn from a PHY manufacturer's EVK schematics and layouts. TI (especially), NXP, Microchip show correct magnetics/ESD part numbers and placement - the trickier thing here is finding an EVK that doesn't just use an integrated MagJack.
I've seen KiCAD running in the browser, so it's not like this isn't completely doable. It's just a question of resource allocation.
Can you speak to how you're sourcing these, and from where? (And would you sell me one?)
The sad answer is that yes, it is that low.
The better answer is that as PCB manufacturing gets more hands-off, we can look forward to some "PCB totem" somewhere in your city, like those self-service photo printers that exist now.
North America: OSH Park
Europe: AISLER
Doesn't Airplay switch you to other media on your device (e.g. Reddit, Youtube, etc) while browsing while streaming?
I've spend around a month on the PCB as a hobby, next to a full time job.