Joe Scotto's Split Keyboard Gets Away with Just One Microcontroller, Thanks to a VGA Interconnect
Using a 15-pin VGA cable to connect its two halves, this clever hand-wired split-layout keyboard gets away with a single microcontroller.
Handmade keyboard enthusiast Joe Scotto has put together a split design with a difference: it uses a VGA cable to connect the two halves together, allowing the entire keyboard to run fro ma single Arduino Pro Micro microcontroller board.
"[I] went with the VGA [connector] as I already had the cables," Scotto explains. "I eventually want to do something with bigger connectors like printers used to use. Normally a split keyboard connects two controllers over I2C with a TRS [Tip Ring Sleeve] cable. That isn't an issue if you like wasting two controllers with a single board — however, I don't like that. Luckily getting around this isn't all that complex: The matrix just has to be passed from one half to the other."
Being able to pass inputs on the keyboard matrix from the controller-free half to the controller in the other half is a neat way to handle the problem and drop the bill of materials in a time of ongoing component shortages — but it comes with a need to find a cable with at least nine wires to handle Scotto's layout. The solution: a VGA cable, which has a total of 15 wires available for use.
"I already pretty much designed a split keyboard called the Scotto Fly, it just wasn't actually split into two halves. It also happens to be my favorite board that I've designed because of its comfortable column stagger and thumb," Scotto explains. "I figured why try something new when I know it works so I simply split the existing board in half and added the VGA connectors."
The resulting keyboard, which is hand-wired rather than using a printed circuit board, uses a minimum of parts: Outemu Blue mechanical switches under DSA Astrolokey keycaps arranged in a matrix split across the two halves, with an off-the-shelf VGA cable serving to connect them into a single matrix that can be read by an Arduino Pro Micro microcontroller running the QMK keyboard firmware.
More details on the build are available in Scotto's YouTube video, while all his designs have been published to GitHub under the reciprocal Creative Commons Attribution-NoCommercial-ShareAlike 4.0 license.