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A ZELDA GAME & WATCH TURNED INTO A RETRO CONSOLE

Turn Nintendo's Zelda Game & Watch into a pocket emulator with about twenty classic systems, save states and a microSD slot for your games.

by Sylver Bruneau

FULL CAD BOM FIRMWARE DOCS

Open-hardwareDisplays

difficulty
●●●●○
time
a weekend-plus
license
GPL-2.0
repo
repo ACTIVE197 stars

WHAT YOU’LL NEED

Videos
1
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COMPAREE VERDICT

This turns a Nintendo Game & Watch into a pocket emulator for NES, Game Boy, Sega Genesis, PC Engine, Atari, MSX, Pico-8 and more, about twenty systems in all. The hardware mod means replacing the stock flash with a 64 MB MX25U51245GZ4I00 (1.8 V SPI flash) and adding an RT9193-28GB LDO regulator, a 100k resistor, two 1 µF capacitors and a flex PCB adapter with a microSD slot. You either cut the back shell or print a replacement. The software unlock uses gnwmanager with an ST-Link v2 or another supported debug probe to back up the original firmware and flash the Retro-Go bootloader; the recommended dual-boot install keeps Nintendo's original firmware on the device. The README lists supported systems, walks through the install (with video links), explains how to structure the SD card and documents cheat-code files, cover-art thumbnails and multi-language Zelda 3 assets. Pre-built binaries are in the releases. The one thing most likely to go wrong is lifting a pad during the flash-chip swap: it is fine surface-mount rework on a tiny chip, and if you have never done SMD rework, this is not the project to learn on. If you can handle that and you want a genuinely portable emulator that fits in a pocket, this is as good as it gets for the form factor.

GOOD TO KNOW

  • —Flex PCB Gerber files for three designs (Mario and two Zelda variants) are in the repo under assets/.
  • —The component list is complete and itemised in the README: 64 MB flash chip, LDO regulator, resistor, capacitors and the microSD slot.
  • —Firmware source, build scripts and a pre-built release binary are all present. The repo includes gnwmanager integration and Docker build steps.
  • —The README walks through hardware install (chip swap, flex board, shell cut or 3D-printed back shell) and software unlock (ST-Link + gnwmanager), plus first-boot SD-card setup. Video walkthroughs are linked.
  • —Licence is GPLv2, with some components under MIT and the Fusion Pixel Font under SIL OFL 1.1. GPLv2 allows commercial use, but anyone who distributes the firmware must also provide its source under the same licence.
  • —No BOM CSV or interactive schematic; you copy the part list from the README by hand.

Can I build this?

PrintOptional: 3D-printed back shell (STL in repo) if you do not want to cut the original shell for the microSD slot.
ToolsSoldering iron or hot-air station, tweezers, flux, microscope or magnifier, an ST-Link v2 or other gnwmanager-supported debug probe, Python 3 for gnwmanager and the build scripts. Optional: Docker if you want to build the firmware yourself.
SkillsFine-pitch surface-mount soldering and chip rework, basic JTAG/SWD flashing, command-line comfort. If you have never done SMD rework, this will be hard.
TimeA weekend if you have done SMD before; longer if you are learning. The flash-chip swap is the slow part.
CostThe README lists the parts (64 MB flash chip, LDO regulator, three passives, microSD slot and a flex PCB made from the Gerber files) but gives no prices.
SafetySoldering iron heat. Lithium battery inside the device. No mains voltage or lasers, but do not short the battery leads.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

Videos

Zelda Game & Watch Turned Into An EMULATION POWERHOUSE!24:17

Community build and walkthrough by Macho Nacho Productions (February 2026); the description credits Sylver and links the repo and gnwmanager.

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Gallery

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the README's Installation section in full — it links the hardware video and the gnwmanager install guide.
  2. 2.Install gnwmanager (Python tool) and connect your ST-Link v2.
  3. 3.Run `gnwmanager unlock` to back up and unlock the console.
  4. 4.Install the 64 MB flash chip (MX25U51245GZ4I00) — the README links a video walkthrough.
  5. 5.Flash the patched bootloader for dual boot: `gnwmanager flash-patch zelda internal_flash_backup_zelda.bin flash_backup_zelda.bin --bootloader` (or `mario` for the Mario model), then power on with GAME+Left and check the bootloader detects the 64 MB chip.
  6. 6.Install the SD card mod (flex PCB adapter, RT9193-28GB regulator, resistor, capacitors and microSD slot) following NaGa's install video linked in the README, then cut the shell or print the replacement back shell.
  7. 7.Download the latest retro-go_update.bin from the releases page, copy it to the root of a FAT32 or exFAT microSD card, insert the card and power on.

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

KNOWN ISSUES

  • You can lift a pad or bridge pins during the flash-chip swap.
  • The README specifies the MX25U51245GZ4I00 (64 MB SPI flash, 1.8 V) or bigger. Check that the bootloader screen shows "MX25U51245G (64MB)" before you continue.
  • Some CMSIS-DAP debug probes drop LZMA chunks at gnwmanager's default speed and report BAD_DECOMPRESS. Lower the speed with `--frequency 1000000`.
  • If you skip the backup step (`gnwmanager unlock`) and the flash goes wrong, you have no way back to the original firmware.
  • The first boot after flashing the update file creates the SD card directory tree (/cores, /bios, /roms). If you interrupt it, the folders are missing and sdpush commands fail. Wait for the launcher menu before unplugging.
  • Cover art must be .img files (JPEG with .img extension), not PNG or BMP. The repo includes a Python script (gencovers.py) to convert them.

Can I keep the original Zelda games?

Yes. The README recommends the dual-boot install (`gnwmanager flash-patch zelda ... --bootloader`), which keeps a patched copy of Nintendo's original firmware next to Retro-Go. With the patched firmware installed, you press GAME+Left at power-on to reach the bootloader.

Do I need to cut the shell?

Not if you print the replacement back shell designed by Aradia (STL in the repo, made for the GnW_SD_v2 flex PCB). If you cut the original shell, the README links facelesstech's drill jig on Printables.

What if I do not want to solder the flash chip myself?

The README lists two people who do professional installs: Sylver (Europe, u/Sylver7667 on Reddit) and hundshamer (USA, u/hundshamer on Reddit).

Can I build the firmware myself?

Yes — the Makefile and Dockerfile are in the repo. You need arm-none-eabi-gcc v10+ and Python requirements.txt. Or use the Docker image (sylverb/retro-go-sd-builder on Docker Hub).

What systems run well?

The README lists about twenty emulated systems, including NES, Game Boy and Game Boy Color, Sega Genesis, Master System, Game Gear, PC Engine, MSX, Atari 2600/7800 and Pico-8. Game Boy Advance is experimental and SD-card only with choppy sound, PC Engine CD and Amstrad CPC6128 are beta, and Atari Lynx is experimental.

Where do I get the BIOS files?

You provide them. For example, FDS games need /bios/nes/disksys.rom, PC Engine CD needs /bios/pce/syscard3.pce. The README documents each one.

Community builds

No community builds yet — be the first, we feature the best ones.

Discussion1

FROM THE COMPAREE TEAM

The README says up to 1,000 ROMs per system are visible, and dual boot keeps the original firmware. What would you load first — NES, Game Boy, or something else?

CompareeTEAM4d ago

Verification notes: the README links a community SD-mod install video by NaGa and a flash-chip video, the Macho Nacho Productions build video links back to the repo and gnwmanager, and the three flex PCB Gerber files sit in assets/ as ZIP archives. Worth an extra afternoon: cover art, which the repo's gencovers.py converts to the .img format the launcher needs.

Sylver Bruneau

Sylver Bruneau (GitHub sylverb) maintains Retro-Go SD, the Game & Watch emulator firmware with SD-card support, and also does professional installs in Europe. The SD flex PCB designs in the repo come from Tim Schuerewegen / hundshamer and PrimoAngelo, and the unlock and flashing step uses Brian Pugh's gnwmanager.

GitHub

Star the project on GitHub

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