The Neo Geo community is currently buzzing over a breakthrough in console modification: NeoPico HD. Developed by fliperama86, this open-source project provides a “pure digital” HDMI solution for the Neo Geo MVS (specifically the MV1C) for a hardware cost of roughly $5.
By utilizing the newly released Raspberry Pi Pico 2, this mod bypasses traditional analogue-to-digital conversion, offering a signal quality previously only seen in high-end FPGA-based solutions.
Technical Overview: The Power of RP2350
The heart of the NeoPico HD is the RP2350B microcontroller (found on the WeAct Pico 2 or official Raspberry Pi Pico 2). Unlike its predecessor, the RP2350 features a dedicated HSTX (High-Speed Transmit) peripheral, which allows it to generate HDMI-compatible signals natively without heavy CPU overclocking.
Key Features
- Resolution: 480p HDMI output (achieved via 240p line-doubling).
- Pure Digital Path: Taps 15-bit RGB signals directly from the NEO-B1 chip before they reach the console’s DAC (Digital-to-Analogue Converter).
- Advanced Brightness: Full support for the Neo Geo’s unique DARK/SHADOW signals for accurate colour representation.
- Digital Audio: Captures audio from the I2S bus, resampling it from the Neo Geo’s native ~55kHz to a standard 48kHz for HDMI compatibility.
- Zero Lag: Uses a scanline-by-scanline output method to ensure no frames are buffered, providing a lag-free experience essential for fighting games.
How it Works
The developer split the heavy lifting between the two cores of the RP2350 to maintain a stable 60Hz signal:
- Core 0 (Capture): Uses the Programmable I/O (PIO) state machines to capture 18 bits of video data (RGB555 + Control signals) at a 6MHz pixel clock.
- Core 1 (Output): Utilizes the HSTX to output the HDMI stream, including “Audio Data Islands” for embedded sound.
- Optimization: A hardware interpolator and Look-Up Table (LUT) handle the conversion from the Neo Geo’s RGB555 format to the HDMI-friendly RGB565 in a single cycle.
Implementation & Requirements
For enthusiasts looking to build this, the hardware requirements are incredibly minimal:
- Microcontroller: WeAct RP2350B (approx. $5).
- HDMI Port: A basic breakout connector.
- Wiring: Approximately 20 wires soldered to resistor tap points on the MVS board.
While the current prototype uses manual wiring, fliperama86 is developing a custom PCB to simplify the installation. This board is expected to include an FPC (Flexible Printed Circuit) connector to reduce the amount of direct soldering required.
Project Links & Future Development
The project is fully open-source, allowing the community to audit the code and contribute to its development.
- NeoPico HD Main Repo: fliperama86/neopico-hd
- PicoHDMI Library: fliperama86/pico_hdmi
Future Goals: The developer has stated plans to bring this mod to the Neo Geo AES (home console). This will likely require an additional daughter board containing an Audio ADC, as the AES handles audio signals differently than the MVS.
[thanks to Furrtek for the heads up]
its a shame theres nothing like this for snes and megadrive