Can someone check my schematic for my 8x8x8 3D LED cube?

I got the original schematic from this link: 8x8x8 LED Cube Kit Schematic | PyroElectro - News, Projects & Tutorials but I wanted to change a few things.

How it works: Using output enable pin, Arduino can "turn off" the 8 74574 then send the data over the shared bus. 3 more bits from Arduino are fed through 74138 3 bit binary to 8 line selector which then triggers the clock input, causing the target chip to load the data. Once all 8 bytes are sent, Arduino toggles the OE to make all 8 rows of LED light up. Anode side of LEDs are connected to these chips. Using OE pin ensures there's no ghosting as the plane changes.

The plane are selected via transistors to sink current from cathode. Each transistor pairs handled up to 64 LEDs per plane.

But it wasn't perfect, it was a cheap design so I wanted to make changes. My revised (and hopefully easier to read) design:

The changes are as follow:
One: The original design uses 74574 to handle a row of 8 LEDs (8 ICs total for one whole plane) but the chip can only source something like 30mA and that won't be much if all 8 LEDs were lit at once. I added MIC2981 on the output of each 74574 which can source upward of 500mA. 500mA is way more than enough to handle 8 LEDs per IC.

Two: 2 transistors in parallel per plane seems like a sloppy design. If the transistors aren't a perfect match, one would end up sinking more current than it's partner, and can potentially blow out. I used ULN2803A which is 8 sets of darlington transistors. ULN2803A is specifically for 5v and can handle 500mA current, which should be enough for 64 LEDs at once at about 7-8mA per LED (accounting for voltage drop across the transistor networks). 200 ohms resistor should be the closest ideal value for LED that are red, yellow, amber, and green. (blue, violet, and white requires more voltage and resistor would need to be adjusted) It is possible to stack a second ULN2803A on top to get max 1A for brighter LEDs but it'd still be a messy design. I have heard people suggest 2003 instead but it only has 7 I/O per IC and I would need 10 total to handle all 64 anodes of an active plane.

Three: there's 2 sets of current limiting resistors: one on the anode end per active LED, and one on cathode end for all 64 LEDs. This IMO is really awful design with one resistor being shared across multiple LEDs which can cause uneven brightness (and with all 64 LEDs on, about 2.5w total through a single resistor!!!), so I removed the resistors from cathode side and added it to anode side (200 ohms per LED now)

Other parts: all the 0.1uF capacitors are places next to each one of the IC (17 total), a pair of 10uF capacitor near the 5v input, 512 green LED (typical 1.8v, max 20mA) and then a resistor and LED pair to indicate power on board. The power indicator LED will be removed when I am done assembling and testing to avoid stray distracting light once I am using the 3D cube for displaying.

Does it look good or should I adjust for something?

Hi,
Please post your schematic as an exported jpg and attach it to your post, this should increase the resolution.
Also can you post it as black ON white, rather than colours on black.

This is the original circuit.


Thanks.. Tom... :slight_smile:

The schematic you posted isn't the full schematic as it's missing the cathode side driver.

Here's a black on white version: