Over the past ~8 years I’ve bought and used at least a dozen of those el-cheapo HDMI2AV converter boxes. having had a few, I’ve broken one or two and noticed the electronics inside are quite sparse. they tend to get very hot (especially the version integrated directly into the plug, the first one of those i had baked itself right off the solder!) and i have a habit of just breaking them open when i get them and adding a chunk of offcut aluminum and some paste to stop them from baking themselves.
I’ve also noticed in my many years of collecting and using outdated video hardware that lots of portable devices, mostly projectors and camcorders, compact the traditional 3-RCA ports into a TRRS 3.5mm jack, and then supply a breakout cable. i also recall having a headrest-mount tv set as a kid that piped mono audio and video to the second unit over a standard TRS aux cable.
that all being said, the chip in these converters take a straight HDMI or displayport input (which can be traced to a USB-C) and turn it cleanly into composite video, with programmable EDID to boot, and then could be output to a 3.5mm jack, and perhaps crammed into the exact same card enclosure used by the DAC for the framework 16.
it would also be EXTREMELY silly to take it a step further and add an RF modulator to the mix; in my case to use my old Sony Watchmans as portable, wireless monitors, for example to watch something while the laptop is in my bag.
It is literally decades since I (worked in television and) routed/switched analogue video. I still have a Barco 12” reference monitor in the shed. One day it will go to e-waste…
I have zero use for the dingus you’re contemplating but I’d buy one just because.
I wonder if you’ve considered clocking and scan conversion. It seems to me that any hardware from “back in the day” could not do anything useful with 120 fps 4k composite video.
yeah. the nice thing about these converters is the little EDID thing inside has basically a wildcard for it’s modes, you can give it 4k and it’ll chew it down but i usually use one of the aspect ratios of 576p so as to have the pixels be more or less same the height as the scanlines, and have a properly proportioned image horizontally.
also consider selling that monitor. someone somewhere would want it if you don’t, i’m 100% sure.
the “dead” unit i had turned out to work. so instead of carefully taking it apart with a hammer, i spudged it open with a flathead screwdriver. it came apart easier than expected.
this is a different unit from the one i recall breaking apart. it has a whole corner of the PCB absent, likely to cut costs. the actual circuitry is incredibly sparse, taking up what appears to be less space than an expansion card. looking good.
upon closer inspection one might find that not only is the closeup upside down (oops) but there’s some silkscreen with a model number. 15 seconds of googling and i find the model of chip used, the “MS1836”, whose name is in the model number.
these appear to be available almost anywhere, (notably i saw JLCPCB has them as an option) and be directly wireable into the DP and usb (for power) of the C-port with just a smattering of support components. this project is looking alot like an hour or two of KiCAD and a simple enclosure swap of the framework DAC once the complete board is ordered. maybe a little heatsink on the chip, and if i want to be fancy, the “MS1836” has a built in MCU and dedicated connections for a small flash chip if i want the settings to persist after loss of power, which is suspiciously absent on the unit i have. maybe it gets it’s settings from the GPU? idk.
i’m going to put a board design together and if i’m happy with it, i’ll get one made.
is there a way to get the aluminium audio card enlosures from framework firsthand? it would be really cool if this project could come out that “well-polished” with so little effort.
it’d look super snazzy with a little red, white, and yellow decal next to the port.
It looks like theoretically CH7215A may be what you want as a single chip solution, though unclear if there is anywhere you can buy it. It’s a single chip part that also integrates the necessary USB-C Alt Mode negotiation and billboarding.
The footprint and pinouts are probably the least of your problems, if that thing needs firmware/configuration you probably need to get them from the manufacturer which likely won’t give that to you for just a few samples. With luck there is a sane default firmware/config on it but I would not bet on it.
good to know. i should have considered that seeing as both of the chips have MCUs.
i already have pinouts and footprints. what i meant by that comment was that JLCPCB might carry the first part but does not have record of the Chrontel chip, thus i probably cannot source it through them.
this is looking a bit like i might have to consider my original plan of desoldering the MS1836S from an existing converter, and maybe trying to use level converters like the original design had pads for. at least, i think that’s what they were. they’re between the hdmi and the chip in the pictures above. U1 and U3.
my goal here is to figure out what’s worth doing before making/ordering boards.
i also might add that both chips include a pin to select between the internal/MCU or an external one.
