The schematic for the
3D LED cube is shown in
Figure 5. The cube is a
16 x 4 multiplexed display,
with 16 common cathode
connections and four
connections. Each LED layer
has 16 LEDs with one
common anode. So, a total
of four layers means four
connections. Each of four
LEDs in a vertical line have
a common cathode
connection. So, 16 vertical
lines means 16 common
Figure 6. LED tester schematic.
The layout for the jig is
shown in Figure 8. The jig
itself is made from 6” x 6”,
3/8”-1/2” thick wood. (The
construction manual that
comes with the kit has
information on building your
own jig.) The 16 holes with
red numbers are 7/32”
diameter, or a #7 drill bit.
LEDs are inserted upside
down into these holes.
The four holes with black numbers are .047” in diameter; so that’s a 3/64” or
#56 drill bit. These holes are used to hold thick tinned wires (about 0.8 mm wire
without sleeve) in place. The four holes with blue numbers are 0.25” in diameter, or a
1/4” drill bit. Drill these holes to hold 1/4–20 bolts at the required positions. Be sure
to label the jig with the diameters of the holes so that you can orientate it properly
later. You’ll need to use spacers and nuts with the jig to achieve a height of 0.75”
between the layers. If you don’t use a jig, your goal is to stack up three to four nuts to
achieve a height of 2 cm (0.75”). The four 1/4” holes hold bolts (like the one in
Figure 9) to which the LED holders attach to keep the layers one above the other at
accurate positions. (This is actually not as complicated as it sounds; the photos should
help.) Bolts are a minimum of 4” long. The 16 holes in the 4 x 4 grid are 13/64” in
diameter (or a #7 drill bit). These holes will be used for making individual layers. Figure 10 shows the jig base.
LED Layer Holders
The holders are used to keep the
layers at their required position above
each other. We need a total of 12 holders,
divided into two groups of six. Please note that
both groups have minor differences (see Figure 11). Figure 12 shows the strip
designs. Use this layout in Figure 12 to make the strips. Glue the layout on 16 gauge
sheet metal. Cut the sheet metal along the border lines with tin snips. Then, use a
hole-punch to mark the centers where the cross lines intersect and drill the holes
with the proper bits. The holes in the LED holders are 17/64” as opposed to 1/4” in
the jig base. This slight increase in the hole allows for adjustments when positioning
the LED layers. Holders are made from 1/8” acrylic.
The 6” x 6” jig wood base.
the 4” bolt
46 August 2011
Check Those LEDs
While the failure rate of new LEDs is extremely low, I recommend checking your LEDs
before soldering them into the 3D matrix structure. It is very difficult to replace a faulty
LED once the matrix is constructed. A simple LED tester can be made to help with this (see
Figures 6 and
7). Take a two-battery AA or AAA battery holder and solder a 1K resistor in
series with the black lead to limit current to the LEDs. This is shown as the –ve terminal;
the red wire probe is the +ve terminal.
Figure 7. LED tester.
Figure 10. Wood base for the jig;
arrows show the 3/64” holes for
the tinned wire.
Figure 11. View of the 12 LED
holders and 12 spacers for the jig.