> > > AAA > > batteries are cheap, environment friendly (more than button ones) and > have > > more than enough energy for months (or years). > > What I really hate about them is their acid. The sooner or later, > it'll come out and foul up your circuit. >
Well, I don't have so much experience in that field. But I have some duracell cells in a bike light, that sometimes gets all the day outside, and they haven't break for months :P > > > Screen: 10x2 screen with backligth would be more than enough (rotating > long > > text of course), so the device size would be kept small. > > Or, better: an OLED. They're dirt cheap these days. And there's even > a fab in China that has figured out how to please us lazy Western > developers, with data sheets, and even offering matching connectors: > > http://www.buy-display.com/ Wow, they're sooooo cheap! I said the LCD one because it has built-in character display, so it's easy (at least for me) to interact with it. > > > Meanwhile, I did some thinking in the direction of a device without > keyboard, without USB host, and without dongle bay, but still with > the other features. > Also can be developed in the future a usb powered mcu with usb-host (again for keyboad plug-in) and radio that will communicate with the device :P > The voltage of the boost converter for the LCD depends on what the > panel wants. E.g., I have my eyes set on the ER-OLED013-1 (1.3", > 128x64), which has a built-in DC-DC converter, but apparently they > found it too weak, so the external supply would have to be 12 V. > > If the internal converter is sufficient, 3.3 V would do, which could > then also be used for the memory card. Not sure if the memory card > would be happy with just the battery voltage. > According to this[1] it would work until 2.7V and if you plan to use 2032 it corresponds with 75%[2] of battery capacity consumed (being very optimistic, the measures were made with low current discharge), what is not so bad. > > The idea of using a rotary encoder for input kinda grew on me. I > first thought of the one that's coplanar with PCB (EVQWKA), but > the iPad-style encoder may actually be more convenient. It should > also be more comfortable to "dial" an item than to hammer a "next" > botton a dozen times. > Agree with that. I remember to see a curious design in TI documentation[3] using tactile sensors. > > And this is what the critter could look like: > > http://downloads.qi-hardware.com/people/werner/pwsafe/shape-20130909.pdf > > It looks great! [1]: http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Components/General/SDSpec.pdf [2]: http://data.energizer.com/PDFs/cr2032.pdf [3]: http://www.ti.com/lit/ug/slau337b/slau337b.pdf page 14 -- Felix
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