Calculator displays

[Garth Wilson]

(06-05-2018 01:35 PM)teenix Wrote:  

(06-05-2018 09:07 AM)Garth Wilson Wrote:  These dot-matrix LED displays are very small, nice, end-to-end and side-to-side stackable, come in several colors, but are quite expensive:
https://www.broadcom.com/products/leds-a...interface/

Very power hungry though - 16 digits consume up to 5 watts @5V.

That's the absolute max, right? IOW, all pixels turned on continuously (which you'll never have in real life), and maximum brightness, which IMO is too bright unless you're outdoors. I've seen these in a brightly lit lab, and they had to brightness up too bright even for that environment. 1.2W per four characters is the specification for "If you exceed this amount, you may cause irreversible damage." You can set the brightness in software, and the display has its own strobing circuitry, and pixel duty factor is something like 20%. I have a couple here that I keep meaning to try out on the workbench. I just have too much work right now to take the time though.

LEDs do take a lot of current though. I know they've gotten a lot more efficient in recent decades, but my TI-58c and TI-59 were just comfortable indoors and just about impossible to see outdoors, and although TI said a battery charge was good for "up to" four hours, the truth was really more like two hours, even when the batteries were brand new, and to save power, I would leave nothing but a single decimal point in the display when I had it idling between calculations or program runs. Getting the HP-41cx after that was a dream, not just to be able to display alpha, but that I could go up to two years on a set of alkaline batteries, or two months when it was getting used all day every day to control test equipment via HPIL.