I hope you choose to go with 1xAAA. Much higher capacity, low cost, widely available. The case gets thicker and the gadget weighs a bit more. No biggie.
--- Ron K. Jeffries 805-567-4670 On Sun, Dec 15, 2013 at 8:51 PM, Werner Almesberger <[email protected]>wrote: > Now that I have a complete case, I tried to make Anelok run off > battery power so that I can show it off also outside the lab. > > Alas, this turned out to be more difficult than expected. First > of all, idle current (where "idle" means spinning in a while (1); > loop) jumped from 4-5 mA after reset to well above 50 mA after > initializing all the subsystems. > > This turned out to be caused by the solder pads of the OLED cable > somehow shorting one GPIO to ground. The soldering looked fine, > though. Re-soldering the pads made the problem go away for a > moment, then return. It took cutting a groove between the pads > to keep these two apart. > > With that issue gone, a pad further down the line decided to > carry the torch and started to act up at about 20 mA. Well, also > that issue fell victim to a hot iron and a sharp knife. > > These events suggest that the amount of rework I've done on that > part of the PCB has about reached the board's limits. I call this > "rework to death", where you eventually reach a point where every > attempt to fix something just creates new problems. > > > Anyway, so far that area seems to be under control. Then I > optimized some of the GPIO initializations, saving some 400 uA in > total. One surprising find was that setting GPIOs going to > (unconnected) pads to "off" draws some 50 uA per pin more than > setting them to output low. > > Alas, Anelok still didn't make it even to the PIN input dialog, > with its rather moderate energy consumption (about 10 mA). > > > So I kept on experimenting. I added CPU sleep and converted the > timing delays (mdelay) to sleep with wakeup by interrupt (msleep). > Surprisingly, this only reduced the power consumption from about > 4 mA to about 3 mA, and the deeper sleep modes didn't seem to have > any additional effect. > > And Anelok still wouldn't run from battery power alone. > > > Today, I broke all those changes down into reasonably small chunks > and added a few more uses of msleep. Lo and behold, after all > this, it would suddenly be content with just the battery. > > Here's the proof - no cables attached: > > http://downloads.qi-hardware.com/people/werner/anelok/tmp/on-battery.jpg > > The case looks a bit odd because the two halves came apart during > the experiment. Also, the temperature measurement is a bit too > optimistic - ambient temperature was only in the low 30es. > > A quick measurement revealed that idle current can now be as low > as about 1 mA, which would be reasonably close to the up to > 500 uA the MCU alone can draw in the current sleep mode. (It can > go much lower, but this needs more work.) > > > There are more mysteries in power management, e.g., the board > didn't want to start at 2.5 V (from a lab power supply) in one > experiment, while even voltages as low as 1.5 V should be fine. > > While things look better now, the initial poor results may indicate > that a stronger battery may be needed. The boost converter could > also run from a single AAA cell (which would require only a > moderate size increase) but the current unstabilized battery > voltage rail (MCU and RF) would have to move past the/a converter, > which means that the converter would be continuously active. > > As they say, research has shown that more research is needed. > > - Werner > > _______________________________________________ > Qi Hardware Discussion List > Mail to list (members only): [email protected] > Subscribe or Unsubscribe: > http://lists.en.qi-hardware.com/mailman/listinfo/discussion >
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