Battery Life

A project log for CircuitPython Badge

A handheld running CircuitPython and cheap enough for a badge.

deʃhipudeʃhipu 05/05/2018 at 18:380 Comments

One of the most important features of a conference badge is that it has to last through the conference. Which is not that easy, if you also consider that its display has to be visible from a distance in full sun, and that you can't use rechargeable lithium batteries. So I put the prototype badge to a test. I'm using 3 alkaline AAA-sized batteries, and I'm displaying a simple pattern of light and dark pixels, that hopefully somehow reflects what will be displayed on those badges, at least on average. It's also set to 50% overall brightness, which is currently the default setting, as it is bright enough to be visible in daylight.

I'm using a local brand "no name" batteries, because that's likely what a conference will also use, and it's probably the lowest quality I can easily get without ordering from China.

At the 9 hour mark I had a small problem: the tablet I used to run the stopwatch application ran out of battery itself — I forgot to connect it to a charger. But since I made a photo at the beginning of the experiment, I easily fished the start time from the EXIF data, and still can tell the exact time.

It's been 11 hours now, and the badge is still working. The voltage dropped from the initial 4.5V to 3.7V at the 4 hour mark, and to 3.6V at the 9 hour mark. At 11 hours it's at 3.5V. In theory, the badge should work down to 2.8V, so I'm really hopeful for this breaking the 12h mark.