Re: Darn! 15C preorder relisted at Samson. $129
Message #58 Posted by uhmgawa on 2 Sept 2011, 5:15 p.m.,
in response to message #55 by robert rozee
Quote:
why not just design it as a refit into a modern 12C+ casing? the user could then, at the same time, repaint/silkscreen the keyboard buttons and escutcheon too.
That has been on the mental drawing board ever since I was
greeted to a at91sam7l128 COB entombed in a blob of epoxy upon
popping open the first 12c+. But assorted pros/cons exist
for the sam7l relative to legacy voyager models to consider:
The pcb is sized to the keypad area alone. So for use of this
real estate in a new PCB layout, vias must dodge the tactile dome
contact lands on the other side of the board. Blind vias are
one option ($$) or a dual laminated board can be used as a
economical approach to achieve the same (potentially better)
result. (Perhaps clearance exists to extend the PCB into the
LCD area, I'm looking at disassembly jpegs ATM and can't tell
for certain).
The LCD mates to the PCB via carbon ink conductive ribbon,
itself joined to the PCB via an anisotropic conductive tape
adhesive. Freeing that connection requires care to avoid
damaging the carbon ink and new anisotropic adhesive to
reestablish the connection to a new board. Moreover controlled
heat and pressure via a specialized hot bar tool are typically
used to form a reliable seal.
The LCD is a segment configuration using a higher multiplex
rate (lower contrast) characteristic. So perhaps we just want
to displace it altogether with a matrix display. That
decision is the easy part -- finding an off the shelf glass
which suitably fits the existing window area will be somewhat
of a challenge but arguably worth the effort. Plus a graphic
matrix glass will realistically require a separate controller.
If we were incredibly lucky we might find a COG or TAB mount
glass + controller to suit but I wouldn't expect so.
The heat stake posts (at least for the version I'd disassembled)
appear to be hollow and are a total of 9. The hollow core
probably will accept a M1.6 or M1.4 screw which dispenses with
recementing post heads for reassembly. Doing so may have
been planned as a manufacturing option or perhaps the posts
were molded hollow reducing mass to ease the staking operation.
The power supply (finally) is supplied by two CR2032 lithium
coin cells which roughly provide double the energy of three LR44
button cells. This was likely to accommodate the substantially
higher "off" current draw of the 91sam7l, but it is only a plus
if we use a SoC with a lower quiescent current. The lower rail
voltage (3V0) is directly digestible by contemporary SoCs where
the legacy 4V5 supply will require a buck regulator to drop
the voltage in operation and a very low quiescent current linear
regulator to provide "off" voltage regulation for SRAM retention.
I haven't found a suitable linear regulator which could live
in a < 1uA budget. Although use of external nvSRAM and external
logic may allow the entire core to be powered off while providing
true non-volatile storage.
I personally like the tactile feel of the full domes present in
the legacy Voyagers which have a more muted inflection. But
that's just my preference and there is no reason otherwise
why the 12c+ cut/legged domes couldn't be reused.
The 12c+ AFAIK thus far uses surface printed keycap legends which
while a concession to manufacturing economy, are a better starting
point if we'd like to engrave/fill new legends.
Edited: 2 Sept 2011, 5:25 p.m.
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