On 2018-02-12 08:51, sms wrote:
On 2/12/2018 8:03 AM, Joerg wrote:
snip
Simple: When clicking the light on you must stand over it or near it.
It could, for example, issue three short flashes after turn-on for
batt-ok, two flashes for "enough but not for more than a few hours"
and on flash for "it'll be empty very soon".
That's reasonable for a USB powered light with Li-Ion batteries. For a
device running on AA or AAA batteries, not really, because different
chemistry AA batteries have very different voltages and discharge curves.
Battery voltage for primary D, C, AA, AAA, AAAA cells:
Alkaline-manganese dioxide: 1.5V. Linear voltage degradation
NiMH: 1.2V with almost do voltage degradation until fully discharged.
Primary Lithium (LiFeS2): up to 1.83V, typically 1.7V, discharged
if 1.6V or less. Decreasing voltage during discharge, not quite linear.
I have seen a device where there was a switch to flip for NiMH versus
Alkaline to account for the different voltages in order to provide a
more accurate low battery warning, though no option for LiFeS2.
You could provide a zero-cost alkaline-NiMH function swap by, for
example, pressing the on-off button for 3sec. Not necessary though
because more rear lights are a bit dim with 1.2V NiMH and I bet 99% of
riders use AAA cells. So just provide a lo-bat warning for alkaline and
that goes a long way.
Of course, for that to work the IC designers must be competent enough to
include a decent bandgap reference. You wouldn't believe how many aren't.
It doesn't have to be accurate, just ballpark. Mainly because almost
nobody remembers how many hours the recent set of batteries has been used.
Another near-zero cost method would be to provide a coarse timer.
5h-10-15h-20h-25h. Simple RC or relaxation oscillator, one through five
flashes for status, done. Or just count the number of blinks. Serious
riders know how long batteries of their choice will last so they can
then decide at 15h or 20h to change them out.
Product design can be quite simple and cheap if we just think outside
the box and most of all try the designed products ourselves. A bike
accessory manufacturer should preferably hire ... riders.
--
Regards, Joerg
http://www.analogconsultants.com/