GoKawiilA while back, I posted the following on social media:
If you’re unfamiliar, Conway’s Game of Life takes place on a two-dimensional grid of square cells, each cell either alive (1) or dead (0). In each iteration, all live cells that have fewer than two neighbors die of “starvation”, while the ones with four or more die of “overpopulation”. Meanwhile, any dead cell that has exactly three neighbors comes alive — I guess that’s ménage à trois or digital necromancy. Really, you shouldn’t have asked.
Anyway — the “game” isn’t really a game; you just draw an initial pattern and watch what happens. Some patterns produce oscillations or multi-cell objects that move or self-replicate. Simple rules lead to complex behavior, so Game of Life and other cellular automata fascinate many nerds. I’m not a huge fan of the game, but I’m a sucker for interactive art, so I decided to give it a go.
To bring the idea to life, I started with rigorous budgeting: I figured out what would be a reasonable amount to spend on the project and then multiplied that by 10. This allowed me to aim for a 17×17 matrix of NKK JB15LPF-JF switches. Here’s the (literal) money shot:
What do you mean, “college savings”?
While waiting for the switches, I designed the PCB. The switches take up most of the board space, but there’s also some room for Microchip’s AVR128DA64 in the bottom left corner:
3D render of the PCB.
The control scheme for the “display” is uncomplicated. Switch-integrated LEDs are laid out on an x-y grid. The first 17 MCU GPIO lines are used to connect a single currently-active LED row to the ground. The next 17 lines supply positive voltages to columns. At the intersection of these signals, some diodes will light up.
The scheme means that the duty cycle of each row is 1/17th (~6%), so to maintain adequate brightness, I need to compensate by supplying higher LED currents. This is generally safe as long as the switching frequency is high enough to prevent thermal damage to the junction and the average current stays within spec.
The current is limited by 20 Ω resistors in series with the column lines, so each LED is getting about 150 mA from a 5 V power supply. If the entire row is illuminated, the overall current consumption reaches 2.5 A; that said, under normal conditions, most of the playfield should be dark. Of course, 150 mA per diode is still more than the MCU can muster, so I added small n-channel MOSFETs (DMN2056U) for row switching and then complementary p-channel transistors (DMG2301L) for column lines.
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