plusdeck 2c PCI bracket PCB replica

I was inspired by this twitter post about using a plusdeck 2c with a MiSTer Multisystem to load cassette games straight from tape into emulators. I wanted to go the extra mile though and use the serial control of those boards. When I ordered my plusdeck 2c from ebay, it didn’t come with the breakout board. That’s surprisingly not a problem though, because the FCC keeps detailed photos of things getting FCC certified.

Well, that’s pretty easy to redo. That has to be most of the traces. Let’s look at the top for the rest.

They made some interesting choices here, let’s go though them. First is the open/short jumper. this is done as a 2×2 header, where I usually see this as a 3×1 jumper, or even as a 2×1 jumper and if you want it open you just hang the jumper off of one leg. This is certainly a choice, just not one I would have made. But what does that actually do? Well, there’s a digital ground and an analog ground. The digital ground is the ground planes by the serial port, that has a plated hole for the PCI bracket screw so it is case grounded. The top screw does not touch the top ground plane because the analog ground is kept isolated. Does this help? well, maybe. The manual just says to connect it/disconnect it to see if sound quality improves. I guess it’s nice to have the option. The next thing is those resistors by the serial port. Enhance!

So… what’s up with this? The bottom shows that pins 2/3/5 are routed how you would expect. Those constitute the ‘3-wire serial’ interface that’s common these days, no hardware handshaking. And for handshaking loopbacks, I’ve never seen anyone use resistors, just jumper them with wire. But let’s go with it’s a loopback, then does that make sense, the way they routed those traces? I’ll skip ahead and say yes, I think it’s what they did. Maybe they were using an SDK that needed hardware handshaking on the serial library, maybe they didn’t know how to turn it off, maybe they’d never made a serial peripheral… I don’t know why they made this wacky decision, but I replicated it how I think it looks under there

that looks sensible, right?

Now let’s look at some of the schematic I drew and the notes I took about the functionality of the connectors. They used TRS jacks that have built in switches so are they doing anything usef ul with them?

The mic makes some sense, they tried to isolate it from the other audio traces by giving it a dedicated ground.

gotta label those pin headers, especially because I am probably not going to populate a shrouded one

label your connectors, color, polarity, function

I used some salvage connectors desoldered from old pentium 2 era motherboards with a heat gun. They used to be in a monolithic gameport/audio connector block but I freed them. I had a heck of a time finding the software and manuals, but I threw them up on the internet archive so no one else has to dig like I did. I have tested the connection and the software does detect the device, but the control isn’t working correctly. I haven’t gone much farther because I got distracted, but I wanted to post this here because I think this PCB design is correct. I plan to sniff the serial protocol in the future to control this device without the bundled software. The ribbon cable is just available on digikey, the rest of the parts are junk drawer finds.

[UPDATE]

I’m an idiot, everything works just fine. The key thing to note here is that the device expects pin 5 of the serial port (digital logic ground) to already be common with the 12v power supply’s ground on the molex connector. If that’s not the case then you have to short the jumper so that digital and analog ground are connected. My test setup was using a bench power supply for 12v and it was not connected to my laptop’s usb to serial converter ground. A note, you need a female to female de9 cable that’s wired straight through (not a null modem) to make this work from a standard PC serial port. I tweaked a bit of the copper fill and made a note on the silk on the bottom about the digital ground situation.

You can use the original software or the reverse engineered python script: https://github.com/natarii/plusdeckctl

I finally ran out pf boards so I posted the project on PCBWay here: https://www.pcbway.com/project/shareproject/Plusdeck_2C_PCI_slot_board_replica_52a2c934.html

I don’t know how much it will cost assembled from them but I reached out to them to make sure assembly will go smoothly.