The FunKey S is the world's smallest foldable retro-gaming console.
Holding a world's record is great, but we wanted a device that was actually playable and that still could be attached to a keychain.
Reaching this goal required more than just the usual job to shrink everything you can: it required a radical change in the design itself.
The idea to use a foldable clamshell design came up rapidly as the only way to get both a small form factor when closed, and offer the largest screen and keypads while playing.
But this solution also brings a lot of challenges, as the required hinge make connections between the 2 halfs of the shell more difficult.
However, this has been done before in the classic GameBoy Advanced SP, or in many clamshell cellphones from some years ago, so why can't we?
Passed this first design decision, we fixed ourselves some additional goals in order to provide the user a good gaming experience:
have a CPU that is powerful enough to be able to emulate most retro-gaming consoles, up to the PS1
have a good quality screen with a resolution large enough to display even the games featuring small texts
have a set of keys and pads large enough and complete enough to be able to play comfortably
have a built-in audio capability (who can play without sound?)
be able for a 6-year old child to add games and emulators
as an extremely nomad device, be able to stop playing just by closing the console, and restart when opening it just where you left (we call this feature "Instant Play")
Besides the constraint brought by the hinge listed above, the main difficulty is due to the maximum device dimensions that should not exceed those of a (large) car key.
And because of the foldable design, the most constrained dimension is thickness: having a folding screen also means doubling the plastic enclosure around the screen and the other internal parts.
In order to meet these constraints, we had to take more (heart-breaking) decisions:
a CPU with external DRAM chips would take too much real-estate on the PCB, so we had to find a CPU with integrated DRAM
an audio Jack would be very difficult to integrate, so we decided to use an internal speaker instead
an USB C connector is too thick and large, so we used a Micro USB connector instead
a Micro SD connector with external access would be too large, as the required "push/push" mechanism, plus the mechanical design to make sure the card does not get loose make the solution much larger
because of real-estate constraints on the PCB as well as power consumption constraints, we decided to not integrate Wi-Fi and/or Bluetooth
the only keypad technology able to meet our thickness goal is using integrated tactile switches
battery capacity had to be adjusted to the maximum available internal volume, using standard battery dimensions