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osresearch / eink-pricetags

Reverse engineering cheap e-ink price tags
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power: measure during image updates and during redisplay #8

Open osresearch opened 2 years ago

osresearch commented 2 years ago

how many images can we receive before we drain the battery?

osresearch commented 2 years ago

image

drawing the boot screen, downloading a new image and writing it to flash, drawing the new image, and then periodic checkins

osresearch commented 2 years ago

image

periodic checkins seem to keep high power on for a few hundred ms, and low-ish power for about a second.

at idle it is 5.2 uA.

osresearch commented 2 years ago

Plotting energytrace column 4 provides Joules.

Receiving and programming the new image: 0.37J Drawing the screen: 0.01J Checkin: 0.003J Idle: 0.00018J / second

Dual CR2450 batteries have around 1200 mAh @ 3.0V = 13 KJ.

At idle that is 833 days. Adding a screen refresh once per minute is roughly double that, so ~400 days if we're using static stored images.

Sending a new image once per hour is a 50% cost over idle (0.648J / hour at idle + 0.37J for a new image + 0.01J to draw it = 1.02J/hour). That is still 540 days.