A tribute to the cordwood construction of old

Back when electronic components were large and circuit board technology was in its infancy, clever engineers used the 'cordwood' construction to save space. We rarely need that sort of assembly method any more, but when I first saw it, I thought that it was a beautiful example of form meets function in engineering.

The Cordwood Puzzle lit up

I had to make a tribute that combined old and new, and it comes to you in a form of an engineering puzzle!

Packaged as a kit

In order to save costs and make things interesting, I wanted to have the two boards be exactly the same. I designed the board and circuit such that its function depends on its position, and how it is connected. That's part of the puzzle that you'd need to figure out when putting the circuit together ;)

The 2 W resistors are used for their size, not their power rating. The three coloured LEDs are 2.1 V so that you'd only need one resistor value (150 Ω) to drive each of them at 20 mA. This simplified the circuit compared with using other colours, and also gave the board some flair even when it is not powered up. There's an n-channel FET for each LED, where the gate is connected to a pin and pulled high through a 10 KΩ resistor (it's a high value so that whatever drives it only sinks a tiny bit of current). This means that when power is applied to the circuit all the LED turns on, but the state of each LED can also be controlled from a microntoroller.

Each LED can be individually controlled

And if you like it, you can get one for yourself at the Boldport shop! The BoM is here and the (strangely missing ;) assembly guide is here (SPOILER ALERT!). As usual, the design is open source hardware -- get the files from here and make your own version!

The Cordwood Puzzle is based on a previous design codenamed 'deadwood' that I did months ago, but never really documented. It was manufactured through OSH Park with many components kindly donated by oomlaut. The design files are here, and below are some pictures.

It's possible to use regular resistors

I originally found these beautiful resistors at Makespace

These lovely colourful LEDs came from oomlout!

It's hard to see, but there are copper hexagons under the soldermask