VGA display switching with debouncer/multiplexer/buffer circuitry?

[analogix]

Yup, you are AOK with the pull-up resistor and a switch shorting the enable to GND.

Thanks for confirming 

Dont worry about the 74HC00, just keep it simple.

You got me curious though, and I'm open for learning 
I may be way off here, but I'm guessing the purpose of the 74HC00 is to enable MUX1 while disabling MUX2 (and likewise the opposite) just by using a single logic HIGH or LOW to one of its (74HC00) pins?
In other words, the 74HC00 controls two MUX chips at once, and the mechanical switch controls the 74HC00.



... in contrary to a pure mechanical switch solution (to enable and disable the MUX chips) which would be a more complicated wiring setup.
Is that it?



I'd personally prefer using a logic chip to control the 'EN' (enable) pins of the two MUX chips if that means a single high/low signal from the mechanical switch. I haven't looked in detail into how many poles might be needed, but my initial thought is that it would require less poles and be less complicated.
If I could simply send a HIGH (+5V) or LOW (GND) voltage to the 74HC00 to set it into two modes as follows, that would be great!

Yes, do use a 78L05 or equivalent.

A 78L05 will take in anywhere from 7.5v to 28v on it's Vin pin.
Tie it's GND pin to GND.
It's Vout pin will be a 5v supply.
Add 2x 0.1uf caps to the Vin and Vout pins to GND.

A 78L05 has a built in current limiter of 100ma, so you will be safe.

It's available in TO-92 3 pin transistor looking type through-hole package, or in an SO-8 pin ic package.
7805 can be used as well, just that they can deliver up to 1amp.

Sounds like a good solution (having everything on a self-contained PCB instead of relying on additional connections), but in case I do run into problems if the +12V from the Atari video output connector is used for something that drains more power than is available after the MUX chips/78L05 takes what it needs (I recently learnt that the +12V was probably used for whenever the Atari video output was attached to a television SCART connector where the +12V connects to a certain pin on the TV's SCART automatically switches over to the AV input)... then maybe I should add the option of a jumper and power connector on the PCB so that I could easy take power directly from the computer's power supply.

By the way, I found there's a MAX4885 evaluation board available, which I understand takes one VGA input (from a computer's VGA output connector) and switches between one of the two available VGA output connectors (for selecting one of two screens). Though close but not exactly what I'm designing here, I took a peek at its datasheet out of curiosity and found it very insightful as it both explains how it works and has a schematic, so I'm going to study that in more detail to understand this better.

A practical question: the MUX appears to come in a 24 or 32 pin package (I haven't quite understood the differences, but something I'll need to look into), and they're both 'TQFN' packages which I looked up and they seem to be a challenge to hand-solder. Can this be done, or are they meant to be soldered professionaly? I plan to buy a soldering-station (ESD-safe) to replace my cheap & simple soldering irons, but will that be enough to make this possible to do myself, or would it be better to order the PCB with the MUX chips pre-soldered? I believe there are some companies out there that both manufacture the PCB and solder components on them, but don't know which companies do that and the costs.

(image source: MadPCB.com)

[Nominal Animal]

Can [TQFN be soldered by hand]?

If you get a small hot plate and hot air, definitely yes.  Others have described using a custom footprint, with a large plated through hole on the bottom, so they can use a fine tipped iron to solder first the IC pads (one at a time, tip in the corner between the PCB pad and the tiny bit of exposed IC pad), and finally the large center pad from the other side of the board.

I myself am exactly at that stage (and after that, onwards to BGA), having a cheap hot air station (see discussions in the Other Equipment & Products subforum here for which one and what to look for), a tiny (for smaller than 2"×2" or 50mm×50mm boards) USB-C PD hot plate you can get off Banggood for a flash deal for under 15€ right now, and a Pinecil USB-C PD soldering iron with full set of tips.

The existing soldering practice kits and DIY kits I've seen don't have interesting enough components – do get a few SMD LED projects or similar for a couple of USD/EUR each, if you haven't soldered any SMD components yet –, so I'll design my own, based on cheap microcontrollers easily programmed with open source tools (my workstations all use Linux).  (I'm specifically looking at a CH32V305-based isolated UART/SPI adapter, designed to be partially populated for programming and testing as soon as the MCU and a couple of capacitors are soldered.)

You can find a lot of videos about the various soldering methods on Youtube, but be careful: there are a lot of garbage videos, so do check the comments, and skim a lot of videos, to see what works.  I can tell that good flux, isopropyl alcohol (IPA), occasionally acetone, and an old toothbrush makes for a much nicer soldering job and results, for example!

which companies do [PCB manufacturing and assembly]

I use EasyEDA or KiCAD to design my own PCBs.  EasyEDA directly interfaces to JLCPCB for PCB manufacturing and optionally SMD assembly, but for assembly you need to use their parts catalog (which is very easy from EasyEDA, as it even shows the per-component price from JLCPCB or LCSC when selecting components).  You can pick any such EasyEDA design and easily check the price by starting the ordering process, the price calculation is online and instant.

Unfortunately, JLCPCB does not seem to have any max4885 in stock right now.

PCBWay is another, often used by for PCB manufacturing and optionally SMD assembly by us hobbyists, but I haven't personally used them yet (only because JLCPCB is so darned easy to use with EasyEDA).

The assembly is usually limited to components on one side of the board, and I do suggest soldering any through hole components yourself.  I do plan to have components on both sides (just because!), but solder everything on at least one side myself.

As to the prices, you can get a set of ten PCBs up to 10cm×10cm/4"×4" for a few USD/EUR plus shipping costs.  For SMD assembly, there are additional costs that vary, but as a rough idea, the setup etc. fees seem to be on the order of 25 USD/EUR for two/five/ten boards at JLCPCB and PCBWay, plus the part costs of course.

[analogix]

Can TQFN be soldered by hand]?

If you get a small hot plate and hot air, definitely yes.  Others have described using a custom footprint, with a large plated through hole on the bottom, so they can use a fine tipped iron to solder first the IC pads (one at a time, tip in the corner between the PCB pad and the tiny bit of exposed IC pad), and finally the large center pad from the other side of the board.

Good to hear it can be done, although (to me) it sounds very risky.
I was also hoping not to buy any more gear than strictly necessary 
Maybe worth looking into the other option (discussed further down) since this is probably one of the few projects I need to use these kind of components.
 

The existing soldering practice kits and DIY kits I've seen don't have interesting enough components – do get a few SMD LED projects or similar for a couple of USD/EUR each, if you haven't soldered any SMD components yet –, so I'll design my own, based on cheap microcontrollers easily programmed with open source tools (my workstations all use Linux).  (I'm specifically looking at a CH32V305-based isolated UART/SPI adapter, designed to be partially populated for programming and testing as soon as the MCU and a couple of capacitors are soldered.)

That's a good suggestion actually -SMD soldering practice kits!
Judging from several Youtube videos it appears that soldering standard SMD components (ICs with normal legs etc.) is doable with normal equipment. I understand that the key is to add a lot of flux to the areas to be soldered (I've never used flux before, so this will be a new experience).
Probably a good idea for me to practice on a few non-critical practice kits before attempting the project I'm discussing in this thread 

You can find a lot of videos about the various soldering methods on Youtube, but be careful: there are a lot of garbage videos, so do check the comments, and skim a lot of videos, to see what works.  I can tell that good flux, isopropyl alcohol (IPA), occasionally acetone, and an old toothbrush makes for a much nicer soldering job and results, for example!

That's the usual problem with Youtube etc. -to distinguish the trash from the proper information. I'll see if I can locate some good ones, then move on to the practice kits. Maybe I can even find one seller with several different SMD practice kits (so as to save on shipping costs, import duties etc). If someone can suggest one, and specific kits I'm all ears 

which companies do [PCB manufacturing and assembly]

I use EasyEDA or KiCAD to design my own PCBs.  EasyEDA directly interfaces to JLCPCB for PCB manufacturing and optionally SMD assembly, but for assembly you need to use their parts catalog (which is very easy from EasyEDA, as it even shows the per-component price from JLCPCB or LCSC when selecting components).  You can pick any such EasyEDA design and easily check the price by starting the ordering process, the price calculation is online and instant.

Cool!
I still consider myself a novice, but I've spent so much time learning Eagle and built up a small library of additional parts that it would be like starting from scratch to learn another CAD package. Do you know if the above can be done with Eagle too, or if there's a way to order the assembly of certain components from the Gerber file from them (or other PCB manufacturers)?

Unfortunately, JLCPCB does not seem to have any max4885 in stock right now.

Oh 
Do you know if the MAX4885 is a common component which is usually easy to order along with PCBs?
Deciding between 24- and 32-pin versions of this MUX is probably something I should be flexible with depending on what's available.

PCBWay is another, often used by for PCB manufacturing and optionally SMD assembly by us hobbyists, but I haven't personally used them yet (only because JLCPCB is so darned easy to use with EasyEDA).

The assembly is usually limited to components on one side of the board, and I do suggest soldering any through hole components yourself.  I do plan to have components on both sides (just because!), but solder everything on at least one side myself.

That's OK. I enjoy soldering through hole components, so that's no problem. And I can probably design the board to have any SMD components to be soldered by them on just one side.
Good to know about this -thanks!

As to the prices, you can get a set of ten PCBs up to 10cm×10cm/4"×4" for a few USD/EUR plus shipping costs.  For SMD assembly, there are additional costs that vary, but as a rough idea, the setup etc. fees seem to be on the order of 25 USD/EUR for two/five/ten boards at JLCPCB and PCBWay, plus the part costs of course.

Are you referring to ten of the same PCBs when ordering at those prices? I probably only need one (but a spare or two won't hurt, being unexperienced at this).
With a setup fee it's probably a good idea to order a few PCBs though, in case I mess things up, or in case someone else might want one.

[Nominal Animal]

I still consider myself a novice, but I've spent so much time learning Eagle and built up a small library of additional parts that it would be like starting from scratch to learn another CAD package. Do you know if the above can be done with Eagle too, or if there's a way to order the assembly of certain components from the Gerber file from them (or other PCB manufacturers)?

Sure.

JLCPCB takes a ZIP file with Gerbers for manufacturing PCBs.  For SMD assembly, you also supply a CSV file (from Excel, LibreOffice, etc. spreadsheet), and a CPL or Pick and Place file.

EasyEDA is supposed to be able to open Eagle (v6 or later) and KiCAD and Altium Designer files in the online Standard editor, but I haven't tested that myself.

It really is a very hobbyist-friendly schematic and PCB editor, probably more suited to hobbyists than actual EEs.  It's what I've used to learn practical PCB design with for the last few years, marking my designs CC0-1.0 aka Public Domain, so it being cloud-only is no issue for me.  Only now, as KiCAD is getting better, I'm switching slowly to KiCAD.

Do you know if the MAX4885 is a common component which is usually easy to order along with PCBs?

Well, LCSC/JLCPCB did supply EasyEDA with the footprints, so it isn't rare.

However, I would reconsider the choice, and look at TI TS5V522CPWR+74CBT3257C as a replacement for each MAX4885.  If I've understood your needs correctly, it should be similar (but with two chips; one for analog signals and I2C, and the other for H and V sync signals), with slightly lower typical resistance (3Ω vs. 5Ω typical) and slightly higher typical capacitance (8pF vs. 5.5pF), but is available at both LCSC/JLCPCB and Mouser, and for only a fraction of the price of MAX4885.

Most importantly, TS5V522CPWR and SN74CBT3257CPWR are a 0.65mm pitch TSSOP packages (dense, but with SMD legs), which are drag-solderable using a standard iron (using e.g. chisel-like K-tip).  I suspect even the signal routing might be easier, because HSync and VSync are in a separate chip.  These have an active-low Output Enable, so you can put several in parallel to the same input signals or to the same output signals to get N:1 or 1:N selection, without chaining the chips, by only enabling the output on one chip at the time.  Both are in EasyEDA component libraries, too.

The main difference is that the TS5V522CPWR analog bandwidth is "only" 380 MHz –– so suffices for up to Full HD (1080p, 1920×1080 50Hz) and 1920×1080 70Hz ––, whereas MAX4885 is 900 MHz.  For what you are doing, there should be basically zero difference in the signal quality.  And, of course, as I already mentioned, H and V sync signals are routed through a separate chip, SN74CBT3257C.

Are you referring to ten of the same PCBs when ordering at those prices? I probably only need one (but a spare or two won't hurt, being unexperienced at this).

Yep, the same PCB.  JLCPCB does offer e.g. assembling only 2 boards and sending you the rest unpopulated, but it doesn't shrink the setup fees.  Its when you have ten or more of the same boards made and assembled, that amortizes the fees to an easily acceptable level (to a minimal-budget hobbyist like myself).

It really makes more sense to use components you know you can solder yourself for one-offs.  And do note that making bare 4-layer PCBs costs about the same (for 2-10 PCBs) as for two-layer boards, just a few USD/EUR plus shipping; no need to limit oneself to 2-layer PCBs.