TinyCircuits

Question about TinyScreen+ low battery handling

Question about TinyScreen+ low battery handling
« on: June 20, 2018, 04:16:17 AM »
Hi,

After implementing the battery voltage read-out from https://tinycircuits.com/blogs/learn/tinyscreen-battery-voltage
I noticed that the TinyScreen keeps running even on a very low battery level (below 3.5V).

Is there a threshold built into the board that shuts it off after reaching a critical voltage, or does it run until it falls below 3.3V due to being out of power?
Is that ok for the battery life or should we implement some kind of shutdown on a different voltage level?

Cheers
thesko

Re: Question about TinyScreen+ low battery handling
« Reply #1 on: June 25, 2018, 07:05:14 PM »
Hey thesko-

This is a pretty wide topic, good questions. Some answers and opinions:

1. The batteries we sell as well as most similar lithium batteries have a protection circuit that cuts off power around 2.8-3.0 volts, the minimum voltage for these batteries. So there is not a safety concern and should only be a minimal affect on battery life by running it 'all' the way down to the cutoff.
2. TinyScreen+ will generally run down to 2.6 volts, but may act a bit differently when the input voltage is below the 3.3V onboard regulator voltage(such as analog reads, depending on reference, and OLED display).
3. 3.5V that you mention is definitely a low state of charge, it could be a good place to indicate a very low battery and prepare for shutoff.

Thanks,
Ben

Re: Question about TinyScreen+ low battery handling
« Reply #2 on: June 26, 2018, 03:53:01 AM »
Hey Ben, thanks for the reply!

Since I was unable to order your batteries to Germany I will have to check if the once am using right now also have such a protection, but I fear not.

In that regard, I suppose there is no way to trigger a shutdown via code of the whole device, is there?
If not, my approach would be this:
< 3.5V = Disable all logic and render a "final" (low battery) image to the tiny screen
< 3.3V = call display.off()

Are there any other steps I should consider for reducing total power usage to a minimum? Are there any sleep states available for the chip that are compatible with the Tinyduino system?

Cheers and kind regards
Andreas