The Rack box project
The Rack box project was made up a lot of AVR microcontroller modules connected together, controlled pretty much my entire apartment.

When I was young and single I had a lot of spare time. I lived in a tiny apartment and wanted to build electronic modules for home-automation and whatever really. I just wanted to solder and make circuit boards. So I got myself a server rack box, and started making electronics and microcontroller modules to fill it with.

Table of content


Pretty much all electronics I built between 2005 and 2010 went into the rack box project. A lot of it was just to supply and monitor voltage levels, temperature, fuses, alarms, etc inside the rack box itself. But it also included a fair amount of home-automation stuff as well; things like lights, heat, intruder alarm etc. The rack box is a 19” standard server rack box, constructed in steel. It was fed 220V to four power supplies inside, providing 5, 12, 13.8 and 24 volts. Without anything special going on the box drew about 13 watts. Power was supplied from the UPS, so it would stay when in the case of a backout.

All fuses, power supplies and modules were monitored and an alarm would sound if anything failed. A lot of the modules inside were used for this purpose alone, and was one of the reasons why I built the thing in the first place. I wanted something to monitor :) The rack box connected to the outside world through four d-sub connectors, but it also had RS232 serial cables going to my computer.

Since the box didn’t have any airflow, and a lot of electronics inside it got warm. I built a fan and temperature controller to monitor the temperature, start a fan if it got hot and sound the alarm if it got even hotter.

In case something really bad happened the box also has an emergency shutdown function, that cut the main 220V supply to the system. It could be triggered automatically from inside the box or the status panel, I had a lot of ideas for automatic shutdown in the case of fire or extreme heat, but I never got around to it. The emergency shutdown controller had it’s own isolated power supply, connected directly to the UPS.

Stack light and whisky
Stack light with yellow light lit, next to a bottle of whisky.

If anything went wrong a stacklight would flash, and a sound alarm was sounded. This could be pretty annoying, especially at night. That’s why the system had a mute function, which turned off all audible alarms. This was automatically enabled at night with a timer.

Since the whole system was connected to a UPS, there wasn’t any way to detect a 220V main failure. So for that purpose I had a tiny AC adapter not connected to the UPS power a relay. Using that relay the system was able to detect if it was running on battery (the UPS) or the 220V main.

At the end, as you can see in the image gallery the rack box got really crowded, so I eventually began making stand-alone modules what would be placed outside the box with their own AC adapters and voltage regulators. Their signals still went via control cables back to the rack box though.

The project ended when I moved out of the apartment in 2010, I removed all modules and electronics and got rid of the server rack box. I still have most of the modules, and are rebuilding and reprogramming them for other purposes.


  • 5V - 20 amps, electronics, AVRs, LED lights, etc.
  • 12V - 2.5 amps, emergency supply.
  • 13.8V - 4.5 amps, lights, relays, electronics, etc.
  • 24V - 2.3 amps, relays, warning lights.

Status panel

Rack box status panel complete
Status panel for the rack box project, with everything mounted.

To get a sense of that was happening in the rack box project, and to be able to manually control stuff, I built a status panel that I had on my desk in the old apartment. It had LEDs, push-buttons and switches for pretty much everything in the rack box; lights, alarms, fan, mute etc. It was made of a desk box with an aluminium front plate, which made it pretty sturdy.

You can read more about the status panel here: Status panel for the Rack Box project


This a list of all modules that were installed inside the rack box at some point in time. I enjoyed giving them acronym names as you can see in the parenthesis. I have re-published some of these projects, and I plan to re-publish the rest as well. But it’s not at the top of my todo list.


Image gallery

Project: The Rack Box project by Thomas Jensen is licensed under CC BY-SA 4.0 with attribution required.

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  •   Created Mar 08, 2006
  •   Last modified 5 days ago
  • Project status: Scrapped