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Other than the battery door, the 28 seems like a fine example of how to build a calculator not intended to be repaired, and not intended to survive more than five years of heavy usage.
(It's been many years since any company has made calculators designed to survive more than five years of heavy usage.)
Posts: 1,841
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At least the HP-28S _is_ hackable.
Christoph Giesselink demonstrated a wired serial I/O on the Allschwil meetings
(with an HP-28S I gave him especially for this;-)
It was possible to send data in both directions, from and _to_ the HP-28S.
The demonstation was a proof of concept, the target of interest was the HP-42S,
or more exactly to check whether it will be possible to do wired serial I/O on a 42S-like machine.
Since the 28S and the 42S are relatively similar from the I/O point of view,
and the 42S is even expandable with RAM and an optional ROM chip,
with some effort it will be possible to make the HP-42S an I/O capable machine.
The only problems are things like effort/price ratio,
or in other words: Who would pay for such modifications?
I guess the answer would be near to 'noone';-)
HTH
Raymond
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One good point about the HP28 series was that it did not requires a case and the alpha keyboard was distict from the numerical keyboard.