Cordwood Puzzle (First Edition)
The puzzle is to correctly assemble the circuit with the components at hand.
Once completed, all LEDs light up when power is applied.
- Two PCBs (96.6mm x 16.6mm each; ENIG finish).
- 6x LEDs.
- 6x FETs.
- 12x 2W resistors.
- 1x capacitor.
- 2x 24.5mm M3 standoffs.
- 4x 8mm M3 screws.
- A bit of 0.84mm diameter wire.
- No assembly guide.
The Cordwood Puzzle is a reverse engineering challenge and a piece of hardware art all rolled into one. I was very happy with the level of enjoyment I felt while working my way through the puzzle. But I was shocked by how great the assembled puzzle looks. I have it sitting on my desk and it continues to draw my attention with perfect proportions and visual interest.
It should come as no surprise that the aesthetic is simply amazing. After all, [Saar Drimer] is known well on Hackaday for his exquisite user of PCB as an art medium with the help of layout software he designed.
The puzzle here is to assemble the pair of circuit boards and components of the kit without a schematic or instructions. This means reverse engineering the circuit. One twist on the game: the two circuit boards are exactly the same. This means figuring out which traces are actually used for each side of the circuit.
I hadn't previously studied the parts that come with the kit so for me this included looking up the datasheet for the TO-92 parts. I've used these particular components before so I had a pretty good idea of the drive methods for them. If you haven't you'll get the added fun of learning how they work; and easy feat for anyone with access to a search engine.
Heat Up That Iron
Once I had drawn out all of the traces I went through again and used highlighters to delineate the different connections. It was time to assemble.
There's still a bit of puzzle here, as you need to do things in the right order. Once I had a plan there was still a bit of fiddling to get the axial components in the right places all at the same time. Even then it took a bit of extra time as I wanted to make sure everything was straight and perfectly spaced to ensure the final product looked as it should. Despite careful work I must have heated one resistor too much when soldering; it slid without me noticing. A bit of work with two irons corrected my gaffe.
The red, yellow, and green LEDs should be a familiar pattern. The Cordwood Puzzle will make a great traffic-light-like indicator when finished. They can be illuminated simply by connecting the board to a power supply. But connect your favorite microcontroller or dev board and you'll have individual control of all six.
In the 1950s and 1960s inventive engineers saved space by using the 'cordwood' assembly, where components were sandwiched in between two circuits boards. This construction became less useful with reduced component sizes, PCB manufacturing, more compact integration, and surface mount technology, but is still a lovely piece of history. Combining both old and new, the Cordwood Puzzle is a tribute to this construction and to the engineers who came up with it.
The puzzle is to correctly assemble the circuit with the components at hand. Once completed, all LEDs light up when power is applied. When connected to a controller board each LED can be individually controlled. (When connecting to a board, make sure that the I/Os can tolerate the voltage levels that are applied to the Cordwood! Also, make sure that you do not short power and ground!) Unfortunately(!), all the comprehensive assembly guides were mysteriously missing from the kits (if you're up for spoilers, the complete assembly guide can be found here).