Get out the soldering iron and clear your schedule, it’s going to take you a while to assemble this 8x8x8 LED matrix which contains a total of 512 LEDs. We’ve looked in on a 3x3x3 cube, and [Chr], who is responsible for this one, has assembled a 4x4x4 cube before, but this one is quite a leap in complexity. It isn’t just physical assembly problems that increase with scale, you’ll need to consider a power supply too since one layer of a 3x3x3 cube would need at 90 mA, but a single layer of the cube above requires 640 mA to light all of the diodes. Multiplexing is handled per-layer, controlled by  ICs which share 8 data lines and are latched by a shift register. This means the display only requires 11 microcontroller pins for addressing. It is striking how well [Chr] explains the design process, and how cleanly he builds the driver circuits on protoboard. There’s a lot to look at and a lot to learn, not to mention the stunning results which can be seen in the video after the break.

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If you’ve ever wanted to dive in and take a look at how memory hardware is implemented here is a good example of how to implement some latching circuits with ether BJT or CMOS transistors. BJTs require biasing resistors which increases the complexity and power consumption when compared to CMOS. If power consumption isn’t an issue you could certainly make some really fast logic.

Most modern on chip RAM is made using SRAM because it only takes six transistors to implement(vs eight) and is pretty fast. When it comes to density DRAM can get one bit of storage by using a single transistor and capacitor(putting the capacitor underneath he transistor can save even more space). All that said, latches and flip flops are still a very useful (and common) tool when working with digital circuits.

[punkky] has been documenting his adventures building digital clocks. They each use six 7-segment LED displays, but he’s been gradually changing how they are built. The first version used a CMOS BCD-to-7-sement latch on each display, which is tied to a PIC16F627a. For the next run, he added multiplexing, so he could drive all the segments using just thirteen pins. He’s posted a final schematic with code and details of how the clock timing actually works.