NEXTUS - ZX NEXT compatible Handheld (PCB only)

• A pocket-sized ZX Spectrum Next clone:
• custom PCB that turns a Sipeed Tang Nano 20K FPGA board into
• battery-powered handheld running the NextNano core.

Fully assembled PCB boards are available to order from my Tindie store:

Visit my Tindie Store https://www.tindie.com/stores/bobricius/

   ⚠️ Work in progress. Both the hardware and the NextNano core are under active development.
Things may change, and you may run into bugs or missing features.
This is a hobbyist / maker project, not a finished consumer product. 
Please read the *Before you buy* section carefully.

What is it?

This handheld is a carrier PCB for the Sipeed Tang Nano 20K (Gowin GW2AR-18). The Tang Nano 20K plugs into the board and runs the NextNano FPGA core, a ZX Spectrum Next implementation by RetroSilicon. The system boots straight into NextZXOS from a microSD card.

The handheld hardware was designed by Bobricius.
The FPGA gateware, core logic and system adaptation are the work of RetroSilicon.

Features

• Display: 2.8" IPS LCD, 320×240, ST7789 controller. The display cutout is designed for a bare LCD panel with a flex (foil) cable, which needs somewhat more demanding soldering (see Current limitations)
• Keyboard: built-in keyboard using the original ZX Spectrum keyboard matrix layout; footprint for an optional foil keyboard
• Video out: HDMI (via the Tang Nano 20K), 50 Hz and 60 Hz
• Audio: onboard speaker and headphone jack, driven by the I2S converter built into the Tang Nano 20K (connected to the carrier board with 2 wires), plus audio over HDMI
• Joystick port: standard DSUB-9 Atari-style connector, wired to independent FPGA GPIO pins
• USB:
• USB port 1: external USB keyboard, mouse or gamepad/joystick (requires the BL616 companion firmware, see below)
• USB port 2: power-only output, intended to power an optional external HDMI monitor
• The Tang Nano 20K connects to the internal USB wiring with a short USB-C cable
• Power: built-in rechargeable battery support with an onboard charging module
• Front panel: designed as a custom PCB with full-colour UV printing and integrated buttons
• Simple circuit: no active components on the carrier board. It is just 4 resistors for the display backlight, a charging module, a headphone jack, and connectors and buttons
• Easy to build: mostly through-hole buttons and connectors
• NextNano core:
• Full ZX Spectrum Next feature set
• Boots into NextZXOS from a FAT32 microSD card
• Kempston joystick and Kempston mouse emulation (via USB)
• CPU speed switching: 3.5 / 7 / 14 / 28 MHz (boots at 28 MHz)
• Tested software so far (demoscene productions, games, BASIC programs, utilities) reportedly runs without problems

What we offer

Colour: currently only the black version is available. A colour version is planned.

I highly recommend including this front panel with your order.

• https://www.elecrow.com/universal-multi-platform-retro-computer-front-panel-pcb-for-picozx-and-nextus.html

Not included in either version

• Tang Nano 20K FPGA board (buy separately from Sipeed or resellers).
  We recommend buying the version with pre-soldered pin headers
• microSD card (FAT32) with NextZXOS
• Battery: one 18650 Li-Ion cell (batteries cannot be shipped with the order, so you need to source one locally)
• Short USB-C cable (Tang Nano 20K to internal USB), needed to connect the Tang Nano to the internal USB port
• Enclosure (see below)

About the enclosure

At the moment only the front panel and the mainboard are finished.
For the rest we recommend a 3D-printed enclosure.
There is no ready-made enclosure design available yet, so you will need to make your own or wait.
A complete 3D-printable case is planned and will be added over time.

Before you buy: what you need to know

This is not a plug-and-play device. You will need to load the bitstream into the FPGA yourself, and optionally flash a firmware for USB support.

Level 1: FPGA bitstream (required)

A custom NextNano bitstream prepared for this handheld is available for download on our Tindie listing, in the Datasheet section. Flash it to the Tang Nano 20K's onboard flash with:

• Windows: Gowin Programmer, part of Gowin EDA. The free Gowin Education edition is enough. Select the Tang Nano 20K, choose Embedded Flash Mode → Erase, Program, select the .fs bitstream file, then click Program.
• Linux / macOS: openFPGALoader, using openFPGALoader -f .fs. The -f flag writes to flash so the bitstream survives power cycles. Without it, the bitstream is only loaded into SRAM and is lost at power-off.

Once the bitstream is loaded, the following works with no other setup:

• ✅ Built-in keyboard
• ✅ Internal LCD display
• ✅ HDMI video and audio
• ✅ Onboard sound (speaker / headphone jack)
• ✅ DSUB-9 Atari joystick port

Level 2: BL616 companion firmware (only needed for USB devices)

The Tang Nano 20K has an onboard BL616 microcontroller. It is used for programming the FPGA and, with the FPGA Companion firmware, it also handles USB devices.

To use anything on the USB port (external keyboard, mouse, gamepad/joystick), you must flash the FPGA Companion firmware to the BL616 using Bouffalo Dev Cube. For the onboard BL616, both files must be flashed at their respective addresses:

Firmware files and updates are in the NextNano repository.

SD card (required)

NextNano boots into NextZXOS from the microSD card, so the card is mandatory.

1. Format a microSD card as FAT32.
2. Download the latest NextZXOS distribution from .
3. Extract the archive to the root of the card.
4. Insert the card into the Tang Nano 20K's SD slot before powering on.

Current limitations

• Work in progress: the core is an early release under active development. Bugs and changes are expected.
• Networking is not implemented yet. It would require an external BL616 (M0S Dock), because the BL616 on the Tang Nano 20K has no antenna.
• microSD card access is poor. The SD slot on the Tang Nano 20K sits under the USB-C connector, so inserting and removing the card once the board is mounted is awkward. We have not solved this yet. An SD extension cable might help, but it has not been tested.
• Display: the display cutout fits an LCD with a flex cable, which requires slightly more difficult soldering. If you use a display on a ready-made module, the cutout may not fit.
• No enclosure yet (see above).
• NextNano is not affiliated with, endorsed by, or associated with the official ZX Spectrum Next project or SpecNext Ltd.

Contents

Bare PCB

• 1x Mainboard PCB

Bill of Materials (BOM)

Assembly notes: The recommended button height is 7 mm measured from the PCB surface. The front panel is mounted on the mainboard with 4 mm spacers (standoffs) between the two boards.

Choosing your buttons: You can mix and match different button types to suit your taste and budget. For example, you can use cheaper buttons with an actuation force of 1.6N for the keyboard, softer 1N buttons for the control buttons, and a red button for reset.

Just make sure all buttons match the 7 mm height, otherwise they may not fit properly through the front panel.

Links and credits

• Bare PCBs Bobricius Elecrow partner store:
• Hardware project:
• NextNano core, firmware and build instructions:
• NextZXOS distribution:
• openFPGALoader:
• Bouffalo Dev Cube:

Disclaimer

NextNano is an independent community project and is not affiliated with or endorsed by SpecNext Ltd.

The ZX Spectrum Next software core and associated hardware require compatible components and configuration.
Please consult the project documentation before ordering components or beginning assembly.