Anelok: saving more power (1/2)

Ron K. Jeffries rjeffries at gmail.com
Thu Apr 30 02:40:53 UTC 2015


Possible topic to discuss:

Everyone understands you're working diligently to minimize power
consumption, (with impressive results, IMO). This tedious work is
absolutely A Good Thing, no matter what battery you design in.

What do people who will purchase and use anelok consider a minimum time
between required battery changes?

Naturally, I have an opinion, but prefer to learn what others in the
community say. And remember, one hopes the potential market is far larger
than the small number people who frequent this list. (N=<100, my wild
guess).

ron k jeffries


---
Ron K. Jeffries
805-567-4670





On Wed, Apr 29, 2015 at 10:28 AM, Werner Almesberger <werner at almesberger.net
> wrote:

> Revisiting the "empty" battery
> ------------------------------
>
> First an update on how deeply Anelok discharged its battery during
> the first "solo" run, about a month ago:
>
> I put it to the usual discharge test, discharging into a 15 kOhm
> resistor. This is the result:
>
>
> http://downloads.qi-hardware.com/people/werner/anelok/tmp/cr2032-used-up.png
>
> For comparison, this is the result of the original test from February
> and March, with a new battery:
>
> http://downloads.qi-hardware.com/people/werner/anelok/tmp/cr2032-1047h.png
>
> Both batteries were 7 years old Sony cells, so one can compare the
> results directly. The initially new battery crashed through 2.4 V
> after about 1030 hours, while the one that had spent a productive if
> short life in Anelok reached that point after about 500 hours.
>
> So this means that Anelok could use more than half of the battery's
> energy content. And that's still before optimizing any capacitors.
>
>
> Ready
> -----
>
> So far, so good. But it's still not nice that Anelok is merrily
> suckling 0.7 mA (board #2) to 0.9 mA (board #1) from the battery
> while doing absolutely nothing useful.
>
> As a reminder, this is the power saving I had implemented so far:
> http://downloads.qi-hardware.com/people/werner/anelok/tmp/power-saving.pdf
>
> Now I added the remaining two low-power modes:
>
> http://downloads.qi-hardware.com/people/werner/anelok/tmp/power-saving-2.pdf
>
> In "Ready", the boost converter is turned off and the system voltage
> drops from 3.3 V to the battery voltage. An unpleasant side effect of
> this is that the values returned by the touch sensor increase, making
> it appear as if the sensor had been touched, which in turn causes
> Anelok to wake up ...
>
> To prevent this, I added a calm period when entering Ready, during
> which the driver re-calibrates the sensor until it is idle again.
> Upon exit from Ready, the driver restores the previous calibration.
>
> This is far from pretty, but it seems to work most of the time. If
> Anelok switches to AAA in a future design, this whole issue will
> disappear since the battery voltage would be insufficient for the MCU
> and  the boost converter can therefore never be stopped in that
> design.
>
> The result is better than expected: once the boost converter is off,
> Anelok draws only 130 uA on average (I guesstimated around 300 uA).
>
>
> Standby
> -------
>
> Last but not least, there is Standby mode, where the pause between
> samples of the touch sensor is increased from 10 ms to 50 ms. (I
> haven't measured the time the sampling itself takes. Should be a few
> milliseconds as well.)
>
> This brings the average current down to about 55 uA (my guess was
> something < 100 uA).
>
>
> Conclusion
> ----------
>
> With the idle current now pleasantly low, a battery should last for
> a month, maybe two.
>
> But we should be able to still go a bit deeper, maybe below 10 uA.
> The key to this is to use the crystal oscillator instead of the
> power-hungry RC oscillator. Since the crystal doesn't work in one of
> my boards, the firmware currently only uses the RC oscillator, but
> one could introduce a configuration option to change that. (And of
> course try not to break the crystal in the future :)
>
> Next: current-monitoring an Anelok usage session.
>
> - Werner
>
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