Sub-Surface Simon Is a Single-Chip Game — in the Most Literal Sense Possible

Pseudonymous maker "alnwlsn" has built the classic memory game of Simon on a single chip — and we mean that in its most literal sense possible, with all components installed within a Microchip ATtiny84A microcontroller.

"Most of the time when people say 'I fit a game into one chip' this is NOT what they mean," alnwlsn points out of the project, dubbed Sub-Surface Simon. "If surface mount is mounting components on the surface, then sub-surface mount is mounting them BELOW the surface. Any sane designer would tell you that your design can be as small as the chip package it comes in. This is not true! An IC is usually just one tiny square cut from a silicon wafer. Depending on the chip package used (and whether or not it has thermal properties you care about), most of a package is just stamped metal pieces, which are the leads of the component, and excess plastic, which can be milled away to make room for more components."

Thus Sub-Surface Simon was born. The core of the game is simple enough: the ATtiny84 chip drives four LEDs, which flash in a randomized pattern. The player is given the job of memorizing the pattern and repeating it on four buttons — exactly as with Ralph Baer and Howard Morrison's original toy from the 1970s. Where the original Simon was a chunky plastic disc, though, Sub-Surface Simon sits in the same footprint as the microcontroller driving it — with its external components sunken into the chip package itself.

"Milling was done with my CNC mill, but with the motors disconnected and manually turning the knobs," alnwlsn says of the process of getting at the chip's inner workings, exposing the leadframe for connection to the LEDs and buttons. "The general technique I went for in assembly is to solder small wires to the leadframe with hot air, then build up the components separately (doing dead-bug SMD), and then dropping the assembled block of components into place, trimming and bending the wires over, then soldering them onto the needed places with a fine-tipped iron."

"To solder wires onto the exposed leadframe, I found the best technique was to apply some flux, then drop in a tiny slice of solder wire," the maker continues. "Then, you heat the pins externally with a hot air gun. The heat will travel up the pin, and melt the solder. You cannot do it by simply aiming the hot air at the solder itself, because the rest of the pin's metal will carry the heat away. This is somewhat counterintuitive. The same technique can also be used to stop solder from melting when you don't want it to. Clamping those pins in the vice will carry away enough heat to stop the solder from melting."

More details on the project are available on Hackaday.io, along with the source code for the game itself — which alnwlsn describes as "nothing special," unlike the game's physical assembly process.