Troy Denton Documents His Low-Cost, Easy-to-Manufacture USB-Flashable NES Cartridge Build

Troy Denton has written up his and Brad Taylor's effort to build a low-cost custom cartridge, programmable via USB, for the Nintendo Entertainment System (NES) 8-bit console — his first PCBA project.

"As far back as I can remember, I’ve been fascinated with computers. This began with the venerable Nintendo Entertainment System — as a child I often dreamt of making my own NES game," Denton explains. "This interest lasted well into my teen years, when I would read programming how-to’s from NesDev and other corners of the internet.

"Later in life, I met a fellow named Brad Taylor – he was the author of many programming guides for the NES, and just happened to show up at my local hackerspace one fateful day. I had no idea this guy lived in the same country as me, let alone the same city — small world! With Brad’s NES expertise and my PCB design skills, we joined forces to make a USB reprogrammable NES cartridge. This project would be my first foray into PCBA (Printed Circuit Board Assembly), wherein a vendor does all of the component placement and soldering. This was a big deal for me!"

The key aspects of Denton and Taylor's design is that it's low-cost and easy to manufacture, in contrast to commercial reprogrammable NES cartridges which typically rely on battery-backed volatile storage or an SD card. The resulting design is programmable directly over USB, uses non-volatile storage which does not require any battery back-up, and supports the loading and execution of games in the NROM format. The heart of the cartridge is a pair of Microchip SST39SF010 memory devices, compatible with the 5V logic of the NES, along with an ATtiny-based lockout controller and an FTDI FT232H USB interface.

"I took a misstep in choosing an FTDI FT232H USB interface – I had selected it solely because I had previous experience using this chip," Denton notes. "So, we did save some time on having to learn new tools – but at a unit price over $10 at the time, we likely could have found a cheaper option, and simply spent some time learning a new platform. Lesson learned!"

While there were a few issues in the final design which needed to be worked around in hardware — a consequence of having failed to get a prototype fully working before entering production — the cartridge is fully functional, which left Denton going one step further: making his own game.

"Making and selling a cartridge is all well and good," Denton adds, "but I can’t go shipping it with material that I had no right to distribute. To that end, I fulfilled a lifelong dream and created an NES game, Harambe’s Revenge. I could write an entire series of blog posts on how difficult it was to write this game. And for all of my efforts – it is a very basic game. I wrote it entirely in 6502 assembly, and did the graphics myself via GIMP."

Denton's full write-up is available over on his blog, along with a list of lessons learned during the process.