Low Power Challenge: LCD Solar Creatures Live On Sunlight, Sleep At Night

With all those e-paper based projects doing the rounds these days, including in our Low Power Challenge, you’d almost forget that monochrome LCDs were the original ultra-low-power display. Without them, we wouldn't have had watches, calculators and handheld games operating off button cell batteries or tiny solar panels back in the ’80s and ’90s. [Gabor] decided to build a set of gadgets with a 1990s LCD aesthetic, called LCD Solar Creatures. These cute little beasts live on nothing but solar power and provide some amusing animations on a classic seven-segment LCD screen.

The Creatures’ activity depends entirely on the amount of power that's available to them. If their supercapacitors dip below 3.3 V, their micros enter a deep sleep state and do nothing except briefly flash an LED every now and then as a sign of life. When light hits the solar panel, the supercaps are charged up and the Creatures come to life and display a few basic stats. Once the caps hit 4.1 V, they really start their day and run a few programs, including a Game of Life-style simulation and an animation of Euclidean rhythms.

Even in active mode, the complete system uses just 11.4 micro-amps – enough to run completely off the 30×70 mm2 solar panel. The charge circuitry is deliberately kept as simple as possible with just a pair of diodes to prevent the solar panel from overcharging the caps in bright light or discharging them in darkness. The ATtiny85 that runs the show is powered through a 3.3 V LDO and measures the capacitors’ voltage through a 1 MOhm resistive divider.

The Creatures’ bodies are made from pieces of laser-cut acrylic, further adding to the 1990s vibe. Monochrome LCDs might seem old-fashioned, but they’re perfect for low-power projects like this, or, say, making your own wristwatch. Nowadays you can even design your own LCDs and have them professionally made.