Low-Power LCD Display Library

In the world of low-power displays, one might say that ePaper technology is best since it requires no power when displaying a static image. On the other hand, its refresh rate is very slow, making it totally inappropriate for applications like video. Even clocks are generally out of the question if you need a second hand.

As explained in this Technoblogy post by David Johnson-Davis, simple monochrome TFT LCD screens can sip power, while outputting a more usable refresh rate. While a typical color TFT will draw around 20mA of current, the 250x122 ST7302 driver unit he’s been experimenting with (which doesn’t need a backlight, and is readable outside) draws only around 30µA, a multiple-order of magnitude power consumption difference.

He’s developed a new library for these displays, which is capable of fitting onto 4Kbytes of memory, along with an example program. This allows it to run on low-power processors like the ATtiny45 or ATtiny402/412, providing a great option for portable displays. The library is capable of text display in standard and double-sized, and provides methods for plotting points and drawing lines, as well as circles and rectangles.

Code is linked in the write-up, as well as sources for the display, and more background information. While you won’t be able to watch 4K video on this little screen, its refresh rate and low current draw presents a great option for time-sensitive stats under battery power.