Battery usage update

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Here's the latest measurements of the batteries' voltage:

	Left hand voltage	Right hand voltage
30/09/2018	2.98	3.04
06/10/2018	2.98	2.99
13/10/2018	2.96	2.97
20/10/2018	2.97	2.98
27/10/2018	2.97	2.98
10/11/2018	2.98	2.98
2/12/2018	3.00	3.00
22/12/2018	2.98	2.97

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This was getting boring so I used this as an excuse to buy myself an oscilloscope for Christmas :D

Let's focus on the problem: I used a 10 Ohm shunt resistor to get the current used by the MCU of the transmitters. I put a pen under the keyboard to keep a key pressed and got the following:

As expected I found a current peak at 1 KHz consistent with what I set in the software.

Fun fact: you can actually see when the MCU puts the 7 column pins high to check on the key presses.

So, what's the battery usage? 

The current draw for a key kept pressed is:

where:

idle duration

idle current draw

current peak duration

current peak draw

Please note that the number of keys being pressed doesn't change the current draw.

We can suppose this is the behavior as long as you keep typing on the keyboard (Actually the firmware goes back to sleep when it detects no key being pressed for 500 ms, so you have to type at under 60 characters per minute to trigger the deep sleep, which is unlikely).

So, knowing the battery is rated for 220 mAh, we get:

HP: Let's say you work 8h a day. We can suppose you type continuously for half your work hours (a bit of a stretch but bear with me). So 4h per day means the battery lasts:

Not bad.

TLDR: Given the data I collected I can expect the battery to last at least a year. Obviously YMMV.