Assembling the Geekcreit® 8x8x8 LED Cube 3D Light Square Blue LED Electronic DIY Kit

I've been meaning to build an LED cube for a while, and I've wavered between sizes, single color VS RGB, kit VS from scratch, etc, but when I happened on this one Geekcreit® 8x8x8 LED Cube 3D Light Square Blue LED Electronic DIY Kit from Banggood for only US$14.29 (on sale) I jumped. Why? Frankly, it's just cheap. And no SMDs! For other kits and DIY cubes, check out this collection of 8x8x8 LED cubes.

Plus, it has commonly used parts:

8x SN74HC573AN Latches
1x ULN2803 Darlington Array
1x STC12 Series Microcontroller

My kit has a STC12C5A60S2, which according to the data sheet: voltage 5.5-3.5V, 60KB flash, 1280B SRAM, 4 timers, 2-3 UART, and 1KB EEPROM.

Not surprisingly, there's no build instructions shipped with the product, but there's instructions/info available for download buried here. That zip includes:

"3D8 light cube modulo software" - Windows app which I haven't even tried (I use a Mac)
"74HC573" - data sheet for the chip - why just that well known chip? Dunno.
"Program HEX and C file" - C Language source and hex dump
"Schematic" - which includes am (apparently) Altium Protel .ddb file (I didn't attempt to open), and a PDF
"Steps of soldering.pdf" - which is pretty poor. Don't worry, you've got this Instructable.

Don't take any of it as 100% reliable though, as the PDF Schematic includes:

A "MAX232" Dual Transceiver that doesn't exist in the parts and there's no obvious place on the PCB for it to go
A "80C52" Microcontroller which isn't correct - my kit has the STC as above
It shows the latches as 74ALS573

... and the Steps of Soldering shows:

SMDs
A different PCB
Various components not in the kit
Different standoffs (metal vs plastic in the kit)

... etc.

... so who knows how accurate the whole thing is!

Step 1: Equipment and Supplies

The downside of any 8x8x8 LED kit is that there's 512 LEDs that need soldering! So make sure you have an iron that works well and you're comfortable using - you'll be spending a lot of time with it.

Equipment:

Soldering iron
Flush-cut wire cutters (or your preference)
Wire strippers
Desoldering wick/braid and/or desoldering vacuum pump (optional, if/when you make mistakes)
Awl, or pencil, or equivalent thing for punching holes in cardboard
Two alligator clip leads (optional)

Supplies:

Solder!
A piece of corrugated cardboard - at least 5" x 5" x 0.25"
Electrical tape - used to hold parts in place
An extra soldering iron tip (optional, I ended up burning through a tip - see image)
Two AA batteries (optional)

Step 2: Prepare and Solder the Pin Headers

The "top" of the PCB is the side that has the "X" and "Y" axis indicator arrows in one corner.

Each vertical "sheet" of LEDs is held in place by the metal portion of a 8 regular pin headers.

Prepare:

Cut apart the provided 40-pin header into individual pin headers - you'll need 72 of them
Using the flush cutters, cut each one off center - with any luck the plastic will crack and fall off, without ruining the metal pin
Remove the metal pin

Place the pointy end of each one into a white circular hole on the top of the PCB. I found if you heated each pin right at the base of the PCB it would suck the solder right in and stay upright. Along one side there's two pin holes quite close to each other; one is for the vertical LEDs, the other for the common connection.

Make sure each pin is as vertical as possible - it'll make assembly later on easier. Adjust any that are out of plumb - do better than I did ;)

Note: From the pics you can see I soldered the chip sockets first, which was not a good idea.

Step 3: Solder the DIP Sockets

They are not all the same height, so pick the shortest and do those first, then progress the next larger, etc.

Make sure you observe proper orientation by aligning the divots on the ends.

One of my sockets had a busted pin so I had to do a little surgery - see pics.

Step 4: Solder the Other Components

On the top:

J2 : Power connector socket
S1 : Push Switch
D1 : Red LED
R1, R2 : 4.7K Ohm resistors
C1, C4 : Electrolytic 10uf Cap, make sure to get the polarity correct

On the bottom:

R3 - R10 : 470 Ohm resistors
C2, C3 : 22pf ceramic caps (unpolarized)
Y1 : 12Mhz crystal

Unused/optional:

J3 (VCC, GND, P30, P31): put a 3-pin (included, skip VCC) or 4-pin pin-header here for programming
S2, S3: for momentary push-buttons (not inclued), which can be used with custom code

Finally, there's J1, the 10K Resister Array, and that'll be addressed in the next step.

Step 5: J1 - the Resistor Array

Although "J1" is on the bottom, it's close to a socket, so I found it easier on solder it on top. I used some tape to hold it in place while soldering. You'll need to find the common pin first.

Determining the array common pin and resistance:

Lacking any markings you need to identify the common pin.

In general, pick two adjacent "inner" pins and measure the resistance - it'll be twice the per-pin resistance (in the pic it's 19.99).

Then try an end pin and an adjacent one. If it's half the above measured value (in the pic it's 9.96), that end pin is the common pin.

Step 6: Seat the Chips

Make sure you observe proper orientation by aligning the divots on the ends.

You'll probably have to bend the pins of the chips inward. Make sure you do this slightly, slowly and evenly - and ground yourself so you don't have any static.

Sorry, no pics.

Step 7: Prepare to Solder the LED "Sheets"

Polarity and "The Bend":

LEDs are polarized. The positive or anode side has the longer lead. The negative or cathode has the shorter lead and also the rim on the LED on that side is "flat".

The LEDs have to be bent at different points to ensure that the positive and negative portions of the grid don't touch.

The +/positive/anode/longer-lead side gets bent right where it goes into the clear plastic of the LED. It's also bent "down" or perpendicular (to the line between both LED pins).

The other lead, the -/negative/cathode/shorter-lead, gets bent right at the point where there's a flat point in the lead - you should be able to see it or feel it. It gets bent perpendicular to the other lead (so in-line with the line between both LED pins).

The Layer Jig:

Using the cardboard, mark out an 8x8 grid - spaced at 1.5cm.

Get the corners correct and "square", then fill in the edges, then inside. If yours looks better than mine you'll be better off.

Use the awl (or whatever tool) to make appropriate sized holes that will fit the LEDs snugly.

LED Jig:

With another piece of cardboard I made another LED hole and marked off where to trim the leads - after you bend them. Trim them so they'll overlap by ~0.5cm. Increase this if your grid isn't very accurate or you find your bending isn't accurate.

But don't trim them all that way; the ones on the right and bottom edges need one long lead each (see next page's image), and the one LED on the bottom/right needs two long leads.

LED Tester:

I built a tester out of two AA batteries and two alligator clip leads, held together with electrical tape. When the batteries are new it's ~3.2V which is perfect for the LEDs.

Step 8: Soldering the LED Sheets

The +/positive/anode/longer-lead (well, before you cut them)/bent-at-the-base lead points "down" (or towards you in the pic).

The -/negative/cathode/shorter-lead (well, before you cut them)/bent-offset lead points "right".

When the LEDs are loose and have nothing fixed to brace against it's toughest to solder them. So, I soldered the right side, then the bottom. Then placed and soldered each line at a time.

Once complete the whole grid should pop out easily and without bending (see last image).

Step 9: Test Each LED of Each Row As You Complete Them.

Connect the positive side of your 3ish volt power source to the bottom of each column, then drag the negative side along the right side rows of the "sheet". You should see each light up.

If you find a one that doesn't light, check your solder. I had one (shown) that was bad.

Once I finished all of the "sheets" I re-tested them all - you don't want to have to unsolder the completed cube once it's done!

Step 10: Getting the "sheets" on the PCB

Getting all 8 leads seated into the pin headers can be a bit of a trick. Each lead should sink solidly into the pin headers. Make sure the row "end" leads are all facing the correct way.

If you've soldered the pin headers in straight it'll be easier.

Once you've verified it's seated correctly and completely, solder it.