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Project Notes

#269 cordwood

The Cordwood Puzzle evokes an era of stuffing massive components into small spaces without a clear idea of where this is all heading! Introducing the Boldport Club Project #3.

Build cordwood_build_night

Notes

A feature of this kit is that “all the comprehensive assembly guides were mysteriously missing”. i.e. yes, it is a puzzle! If you don’t want spoilers, do not read any further;-)


Unboxing and Parts Count

kit01_delivery_yay

kit02_examine_the_parts

Parts count? All in order, of course. It is unusual and fascinating to see these jumbo parts - 2W resistors and 10mm LEDs. Pretty rare these days, so fun to play with.

Ref Item Qty
- identical PCBs (96.6x16.6 mm each) 2
LED1,LED4 green 10mm LEDs 1142474 2
LED2,LED5 yellow 10mm LEDs 1168543 2
LED3,LED6 red 10mm LEDs 1168543 2
Q1-6 nMOS FET, Fairchild, 2N7000 6
- 2-pin SMD 2.54mm pitch header 1
JP1 6-pin SMD 2.54mm pitch header 1
R1-3,R7-9 150Ω 2W resistors, 9338101 6
R7-9,R10-12 10KΩ 2W resistors, 1602193 6
C1 1uF capacitor, 1549977 1
- 24.5 mm M3 standoffs 2
- 8mm long M3 screws 4
- 0.84 mm diameter wire enough

kit03_basic_circuit_and_boards kit04_construction_complete

Power

The LEDs are rated for 20 mA with forward voltage of 2V. Therefore, with the current-limiting resistor of 150Ω, the maximum supply voltage is 5V.

Construction

The circuit is nice and basic - a 6x array of low-side n-channel FET controlled LEDs. the gates of the MOSFETs are pulled high, so by default all the LEDs are ON. Input lines to the MOSFET gates are exposed individually (the 6-pin header), so an external source can pull the lines low and turn off the corresponding LED.

What is really neat is how this in configured in identical PCBs set parallel to each other. The true test of the “mirrored PCB” design is how many fixups are required .. and the Cordwood is as perfect an example as you will ever find, since the only asymmetry required is the single crossing of the power lines between the two boards.

Breadboard

Schematic

Build

Credits and References

About
Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.