Part of what makes these slightly hard to find, I think, is the rarity of the sockets. The NES is now over forty years old and I doubt anyone's caused a factory to produce more parts for them since at least the year 2000, so anyone making commercial adapters will be doing so in very small quantities.

Mayflash, for example, seem to have given up on that approach entirely, and their adapter uses a 9-pin connector and (I suspect) a butchered extension cable to make it work: https://www.mayflash.com/product/PC053.html

So, the goal for this mini project will be an Arduino 32U4-based adapter with a couple of 3D printed NES controller sockets on it. That could be replicated for well under AU$10 by someone with the right machinery and skills if someone (I'm the someone!) wants to burn some spare time in making a design that will work, and most of that cost is in the Arduino-compatible board - the rest is cents of plastic.

Worst case, I'll build a few with the official sockets, and make those available too.

It'll be weeks before I have any electronic parts to play with, but for now I have a 3D printed socket that perfectly fits the plug on one of my NES controllers. A 0.4mm nozzle isn't fine enough to print walls between the pin shrouds in the connector, so my version will look open like this.

Do you have a 3D printer, a NES controller and half an hour to kill? DM me, I'd love to test this part on other printers and with other random controllers people have in the cupboard.

#3DPrinting

I think, with a 32U4 Pro Micro clone, I can support up to four controllers with all pins wired up. That's clock, latch and 3x data lines per controller, which is 20 in total, but I think I can make the latch pin common to all ports - that's the one that causes controllers to reload their states into their shift registers for reading.

I think the MVP for my adapter will be two ports - both the Advantage joystick and Four Score adapters have two plugs - but a four port variant should be possible.

Reading from a NES Four Score looks trivial.

For a regular controller, which is basically an 8-bit shift register, after strobing the latch pin, strobing the clock pin 8x will reveal its D-pad and button states, and you do the same again on the second port for the second controller.

The Four Score appears like a 16-bit register, so you flick the clock eight times to read player 1's pad, then another 8x to read 3. Then you do the same to port 2 to get players 2 and 4. https://www.nesdev.org/wiki/Four_player_adapters

The Hori 4 Players adapter (15-pin "Famicom Expansion" plug) looks identical to the Four Score in terms of protocol, and while nobody appears to have documented exactly what the NES Satellite does, I'd be very surprised if it did anything differently at all.

Satellites are also not particularly difficult or expensive to get, either. I foresee a new mini collection brewing... but I'll force myself to wait and validate my NES MAX pad working with my adapter before I start acquiring more hardware.

Here's my vision for the NES socket: a #3DPrinting frame for wires bent at a 90 degree angle to be pushed into, with one end pointing out into the socket for a plug to slide onto, the other out of the frame to go through holes in a PCB to be soldered down.

I will also make some sort of jig for precisely bending... some sort of wire. I know not to use anything galvanised as the fumes from soldering it is toxic, so my first attempt will be with 1mm copper jewellery wire - any other suggestions?

@timixretroplays you’ll need to match the wire diameter to the diameter the other end of the plug is expecting. You’ll probably go through a couple of different partial-mm diameter wires to find the right fit that the plug grabs on to nicely. Too thin and the plug will come out too easily (or even not make contact at all), too thick and you’ll push the wires out the back of the socket. Speaking of which, you may want to put some kind of bracing at the back of the wires so they don’t push out…

Also, bend radius is a thing. The larger the bend radius the less prone to breaking…

@jpm I'm fairly sure the original uses 1mm thick pins based on some high resolution photos, but I won't know until one actually arrives (and I've never owned a NES myself).

I have some ideas for better securing my pins in the socket. I might end up with a two-part design. And I have some thoughts about trying something with stainless rods if copper wire ends up too weak.

I couldn't find any projects by anyone else silly enough to try 3D printing a socket like this, so I'm working in the dark.

@timixretroplays oh hm, they're harder to get to than i thought. unsure if i can get one out of its hole without damaging anything

1mm looks about right just holding calipers up in front of it though, not that that's any better than what you had already