#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