Ghosts αSNES

[YveltalGriffin]

MCAD is getting very close to completion!

Just need to wrap up the cartridge slot mounting and ribbon slot, and then I can lock in connector placement and start on the mainboard routing.

 

[loopj]

 

[YveltalGriffin]

Well, I'm making slow but steady progress on the mainboard. I cleaned up the SNES core schematic, which was a disgusting EAGLE mess before because I didn't know what I was doing.

The Super Everdrive schematic is done, and the routing is in progress.

What I'm dreading is the cartridge slot connections. Both the Everdrive and cart slot ZIF connect to the SNES core through level shifter-buffers (so that both can be enabled/disabled at will). That means three different cartridge buses (SNES, slot, Everdrive) need to merge below the 1-Chip in a sane way. Gonna be rough, but I'll figure it out. I'm doing via-in-pad for everything to buy myself as much space as possible.

The build will use iPhone 15 Pro Max loudspeakers. Smartphone speakers have compact enclosures designed by the world's top audio engineers, and little styrofoam balls to make the chamber acoustically larger than its physical volume would suggest. TL;DR they sound very bassy and rich for their size! Have a listen!


With super crisp video that looks like an emulator, and super crisp audio using the Scampi architecture, this portable will be the ultimate way to play SNES on the go!!!

For those concerned about the inclusion of a Super Everdrive instead of an SD2SNES, I get it. I did want to have an SD2SNES initially, but the fact is that the SD2SNES circuitry is outrageously large and complex, while only enabling ~12 additional (good) games to be played:

• Megaman X2 and X3
• Super Mario RPG
• Super Mario Kart
• Pilotwings
• Super Mario World 2
• Star Ocean
• Ballz 3D
• Star Fox
• Kirby Super Star
• Kirby's Dream Land 3
• Doom

And here's the difference in implementation size / complexity between ED (top) and SD2SNES. Note that this is with BGA replacements for the SD2SNES, but not for the Everdrive. The Everdrive could be even smaller with BGA flash.

The SD2SNES also has to be programmed at startup, which is a kinda arduous process involving flashing the PIC, swapping the SD card multiple times, and power cycling it. Super Everdrives, on the other hand, are literally $17 on AliExpress, and the chips can be transplanted with no fuss.

So, in the interest of picking my battles, I will "settle" for 98% library playability via Everdrive, and play expansion chip games via real carts or an SD2SNES in the cart slot. Maybe this compromise will help me actually finish the project

 

[loopj]

 

[YveltalGriffin]

Today I conducted some SNES Jr. undervolting and power measurement tests. Amazingly, the 1Chip system can run from 4V and even 3.8V with no issues besides reduced video levels!

Here are the results. This is total SNES power consumption, including the cartridge, a controller, and Scampi in headphone mode (only a couple mW), but not including the HD Retrovision YPbPr cables (which draw a ton of extra power.)

The power consumption of old consoles varies a lot depending on the screen contents. So, a mostly-white screen will draw a lot more power than a mostly-black screen. This is the cause of most of the power variation between different games in the three categories.

Real Carts

• Super Metroid:
  • 208mA @ 4.00V = 832mW
  • 197mA @ 3.80V = 749mW
• Cu-On-Pa:
  • 205mA @ 4.00V = 820mW
  • 191mA @ 3.80V = 726mW
• Super Mario RPG:
  • 225mA @ 4.00V = 900mW
  • 210mA @ 3.80V = 798mW

Super Everdrive

• Menu:
  • 215mA @ 4.00V = 860mW
  • 198mA @ 3.80V = 752mW
• Paperboy:
  • 227mA @ 4.00V = 908mW
  • 210mA @ 3.80V = 798mW
• Earthbound:
  • 259mA @ 4.00V = 1.04W
  • 247mA @ 3.80V = 939mW

SD2SNES

• Menu:
  • 376mA @ 4.00V = 1.50W
  • 374mA @ 3.80V = 1.42W
• Metal Slader Glory DX
  • 405mA @ 4.00V = 1.62W
  • 405mA @ 3.80V = 1.54W
• Yoshi's Island
  • 352mA @ 4.00V = 1.41W
  • 356mA @ 3.80V = 1.35W

At first, Super Metroid showed an anti-piracy screen at 3.80V, but I think it was because the HD Retrovision cables were sucking too much power. After I got rid of them it worked fine at 3.80V. So, I think I'll use a buck-boost regulator for the SNES core and run it at 3.80 or 3.90V in the final portable. This will cut power and heat nearly in half!

Right now I'm estimating the total system will draw less than 4W when using a real cart or the internal Everdrive. With two Vapcell N40 cells this should let the system run for over 7 hours

 

[Stitches]

What in the name of Ashen is this horseshit?

 

[RegDogg]

What in the name of Ashen is this horseshit?
View attachment 36261

hey atleast he doesn't need IPA to clean his flux, thanks to the alcohol tech

 

[YveltalGriffin]

I've been working on the mainboard routing some more. It's tough stuff.

I chickened out and moved to a 6-layer board. The SNES core routing would've been a nightmare with only two signal layers.

The schematic is only about halfway done. Long way to go...

 

[thedrew]

Those curved traces are a work of art! This whole project is!

 

[Lazr]

I chickened out and moved to a 6-layer board

Well hey, let's look at the bright side, VIPPO is now free!

 

[subierekt]

if i dont have this in my hands by 2026 imma riot

 

[YveltalGriffin]

Made some progress on the audio stuff, including the stock DAC, mixing circuit and Scampi amplifier.

I2S routing detail:

I'm gonna use off-the-shelf Molex Picolock cables for the speakers:

Next thing to tackle is the MST703 LCD driver.

 

[YveltalGriffin]

The MST703 schematic is ~90% complete. Turns out the MST703 driver boards I had on hand were all 18-bit RGB, so they weren't suitable for RE. I ended up basing the design on existing MST70x schematics from CSDN.net, with some spot checks from @thedrew (thanks dude!)

I'm not totally satisfied with the voltage regulation. I need to miniaturize some of the Shinobi regulators anyway, so this is a good opportunity to rethink the overall scheme.

A ~3.45V buck-boost and a 3.3V LDO to subregulate should provide the best balance of efficiency + low noise for the MST's analog rails. Since I don't want to feed the MST a noisy signal either, the Shinobi analog rails will need to be subregulated too. Those are 2.5V, so they'll need a ~2.7V buck. I've been trying to avoid too many chipscale BGAs on this board, but they might be mandatory with how cramped it's getting.

The core also needs to be subregulated to avoid video noise. I discussed this a long time ago, but my approach has changed since then. I found a sick high-PSRR adjustable LDO with only 20mV dropout at 500mA Iout: ISL80102IRAJZ-TK. This LDO will subregulate a ~3.9V buck-boost to power the core.

Ideally I'd use TPS6381x's (Thundervolt's buck-boost) for all these subsystems, but it doesn't have a configurable I2C address, so they can't coexist on the same bus without extra hardware. Might go with TPS631011 instead since the current requirements for each subsystem are so low.

On the layout side, I redid the cart slot routing, connected up Shinobi Scaler properly, routed the speakers, and did the placement for most of the LCD driver circuitry.

After I finish routing the LCD driver, it'll be time to tackle the BMS.

 

[YveltalGriffin]

I've completed the placement and routing for the PD controller, LCD driver, voltage regulators, and the BMS!

The BMS consists of a BQ29732 protector, MAX17055 fuel gauge, and BQ24292i charger. Only the BQ29372 is new to me-- I used both the MAX17055 and BQ24292i on my "new! UltraWii" PMS back in 2020.

I had to sacrifice post-regulation on a number of sensitive rails for space reasons, but it'll be OK. The MST703 has ferrite beads on all of its analog rails anyway.

The board is getting really close to completion. Feels good!

At @supertazon's behest, I designed a 2.5D glass lens for the LCD. When I have time, I'm going to get it manufactured and laminated onto the 5" 640x480 panel. Should look pretty sexy and will be a major improvement over the stock panel's matte finish. What's a little bit more scope creep at this point?

Mainboard in the shell:

 

[Soak_n_fused]

Please tell me you’re gonna take commissions for these bad boys

 

[YveltalGriffin]

Please tell me you’re gonna take commissions for these bad boys

Haha, probably not. But it will be fully open source!

I've been finalizing the layout:

• Power planes on L3 and L4
• Mitsumi V520B and controller ZIFs
• Housekeeping MCU, RGB LED, switches, multipurpose button
• GND planes and GND stitching
• Some more PCB artwork

The housekeeping ATtiny will be able to do a lot of stuff:

• monitor the power switch
• configure the charger and fuel gauge
• drive the RGB LED
• turn on/off VSYS to the entire system
• enable the SNES core voltage reg
• reset the SNES
• enable/disable the cart slot
• enable/disable the Everdrive
• control the LCD backlight brightness

Having a dedicated MCU for the audio amp makes both the layout and coding a lot simpler. (I did the same thing on UltraWii.)

These pours on L4 came out well! L4 is split into two halves: the left side is 3.80V for the SNES core, and the right side is VSYS (battery voltage) for powering all the modern circuitry.

L3 got a lot more split up than I expected, but it's OK because it was always supposed to be the "junk drawer" layer. L2 and L5 are still 100% solid, unbroken GND planes.

Some semi-final board statistics:

• 125 x 96mm
• 480 components
• 2678 pads
• 2145 vias

With the mainboard routing basically complete, it's time to return to Fusion and hash out the cartridge slot mounting and cart slot flex. Tbh, I was concerned I wouldn't be able to match the nice aesthetics of the original αSNES prototype board, but I think it turned out great!