|Re: Form factor for calculators|
Message #29 Posted by DaveJ on 12 Nov 2009, 9:31 p.m.,
in response to message #28 by Paul Dale
I don't think I've seen a credit card calculator in portrait form factor (i.e. they are always landscape).
24 "buttons" seems fairly standard and I'm sure would be sufficient. The 4-banger designs of couple of years back were all based on 20 buttons and they got pretty complex (as in scientific and programmable). The buttons are often laid out in a 6x4 grid (but not always e.g. the Citizen W11S).
Most (all) include a small solar cell beside the display as well.
Thicknesses range from 2mm up and the suggested 4.8mm should be okay.
I think I've come up with a way to make this thing cheaply, using the off-the-shelf LCD I've got, and 4.1mm thick or maybe less.
So picture a credit card size (WxH) calc (actually slightly wider for a portrait calc), just over 4mm thick, with a high contrast 8 digit 14segment display running from a single CR2016 battery replaceable as a "slot in" on the bottom end, along with a standard 0.1" header connector for programming on the bottom edge as well.
No need for an expensive case, it will be an entire sandwich FR4 fiberglass design, with your chose of color on the bottom.
The only major choice is whether to go for a stick-on membrane keypad which would increase the height a bit, possibly afford some extra protection for the glass LCD, but does not add to the power consumption. Or a touch panel interface that does not increase the thickness, but does chew the battery more.
It's actually looking quite easy and cheap, there must be a catch...