[Tim]’s Dice10 is an exercise in minimalism. Building an electronic dice using an ATtiny10 with code that fits within 1kB is not too difficult. Charlieplexing the LED’s would have used three of the four available GPIO pins. [Tim] upped the game by using just two GPIO pins to drive the seven LED’s for the dice. A third GPIO is used as a touch button input. Besides the ATtiny and the LED’s, the only other component used is a capacitor across the supply inputs.
The LED’s are grouped in three pairs of two LED’s and a single centre LED. Usually, Charlieplexed LED’s are connected across pairs of GPIO pins. But his scheme includes connections to the 5V and GND terminals, besides the two GPIO pins. Building a truth table makes it easy to figure out what’s going on.
STATE PB2 PB0 LED's
1 Z Z --
2 L Z LED 1/2
3 H Z LED 3/4
4 Z L LED 5/6
5 Z H --
6 H L LED9
7 L H --
8 H H --
9 L L --
Only the logic states used are listed in the table. It’s possible to add two more LED’s between PB0 and GND and one more anti-parallel with LED9, making a total of 10 LED’s driven by two pins. That’s quite a hack. The important thing here is to have two LED’s in series in the arms that connect to either 5V or GND.
[Tim] has posted the code and hardware source files on his Github repo, and his blog post has some additional details on how he solved the problem.
If you’re looking for more inspirations on minimal dice designs, check this “PIC powered pair of electronic dice” which uses a PIC 12F629 with five outputs driving a pair of 7 pips to make a dual dice.
If you have a cool project in mind, there is still plenty of time to enter the 1 kB Challenge! Deadline is January 5, so check it out and fire up your assemblers!
For starters, he got panels (as in PCB panels) of WS2812 boards from eBay. The advantage is it lets you choose your own pitch and strand length. The flip side is, you need to de-panel each board, mount it in a jig, and then solder three lengths of hook up wire to each LED. He planned for an eight sided star with ten LED’s each. And he built three of them. So the wiring was, substantial, to say the least. And he had to deal with silicone sealant that refused to cure and harden. But nothing that some grit and determination couldn’t fix.
Each digit is made using one pair of Neopixel rings, stacked to form a figure of eight. All the digits are composed of arcs, so readability isn’t the best but it’s not hard either. [rhoalt] does mention that the display is easier to read via blurred camera images rather than visually, which isn’t surprising. We’re long used to seeing numbers composed of straight line segments, so arc segmented digits do look weird. But we wouldn’t have known this if [rhoalt] hadn’t shown us, right ? Maybe a thicker diffuser with separator baffles may improve the readability.
There are 480 LEDs in his display, and he addresses them through TLC5927 shift registers. Synchronisation is provided by a Hall-effect sensor and magnet to detect the start of each rotation, and the Teensy adjusts its pixel rate based on that timing. He’s provided extremely comprehensive documentation with code and construction details in the GitHub repository, including 
