Estimating power consumption, time left for shooting on portable power
if we use some "gauge" system we can do a pretty good estimate. There is no open standard for this of course, but to explain in simple words how it works :
> Each battery pack would have a chip that counts power getting in when charged, and power out when getting discharged (think like putting fuel in a car).
Too complicated for most cases, typical batteries have a very well known curve they follow when discharging, which can be used to calculate the remaining capacity from the voltage.
> This information can be made available trough i2c. The chip managing this must known which kind of chemistry is the battery pack. And also adjust to the efficiency of the battery over time (a battery becomes less and less efficient over time, and 100% in doesn't mean 100%).
IIC interface for voltage levels at the battery and storing simple information about the battery pack in an eeprom are a good idea for custom battery packages.
> There are specific chips for this task available. They are > cheap (like 0.5$).
> So, if the camera has a somewhat constant power need,
Which it doesn't :) We will make sure to power down everything not required during pauses where no recording or viewing happens.
> we could estimate the time left using so called intelligent > battery pack.
> The pack must have the chip for this to work, it's the memory > of past operations ofr this particular pack (averaged discharge > rate, power left, etc...)
> But do we want to make custom battery packs, I'm sure we don't > at this stage.
Correct, but we can keep this in mind for later.
> This, or provide 2 threshold levels for voltage (warning > and shutdown), li-po for example cannot go bellow a defined > voltage, else they are destroyed, or heavily impacted on > performance.
> Having some discharge curves preloaded in camera can help as > well (at least for lipo and to a lesser extend nimh).
> Or of course reverse engineer existing battery packs, who -I > bet- work exactly the same, with the exactly same chips inside.
Here a chip that does exactly that, for 2-4 cells batteries which are in our intended ballpark : http://www.ti.com/product/bq34z100
>>> Being able to set a warning voltage is a plus.
>> Or several (which is kind of what a battery display on >> a smartphone or consumer camera does).