Kiu's KHA Is an "Over-Engineered" Subrack System for RS-485 Smart Home Control
Designed more for the experience than for an optimal solution, KHA delivers a slick smart home experience with industrial flair.
Pseudonymous maker "Kiu" has put his smart home systems under the control of a self-admittedly "over-engineered" modular RS-485 rack-mounted modular system — and has released everything under an open source license for anyone to follow along with their own setups.
"My latest project [is] a modular RS-485 multi-master RS-485 subrack home automation and control system," Kiu explains of the KHA project. "So now I have a 19" rack filled with modular subrack modules or assemblies, and these are connected to nodes I have scattered around my apartment — nodes to illuminate my IKEA furniture, nodes to drive relays for mains power, I have infrared and RF [Radio-Frequency] modules to control non-connected devices."
The system, though impressive, is self-admittedly over-engineered. "I wanted to have the engineering challenge," Kiu says of the resulting design. "There are likely way better solutions out there, professional or open source. I didn't find the optimal solution for any of the problems I stumbled upon, but it was an interesting journey to learn stuff."
The heart of the system is a 19" rackmount chassis with a rear backplane, into which the subrack modules — each its own PCB with a connector on the rear — slot. There's room for a number of modules per main unit, each of which has a front panel with different hardware depending on its purpose: simple buttons, rotary encoders, locking switches, seven-segment LED readouts, analog audio jacks, and more.
Each node in the system is powered by a Microchip AVR64DD32 microcontroller, with inter-node communication taking place over RS-485 communication carried over CAT6 or CAT7 Ethernet cable — along with power, meaning that remote nodes need only a single cable to operate. A push of a button on the main rack can enable shelf lighting, control heating and ventilation systems, or — using custom-built smart sockets fitted with relays — control external non-smart mains-voltage devices.
Kiu has published the whole project on GitHub under the Creative Commons Attribution-NonCommercial 3.0 Unported license, and for those who want to dig deep into its details has also released a two-hour "lecture style" deep-dive into KHA — embedded above and available on Kiu's YouTube channel.