Elf99 - rebirth of a classic

From: Scott McLauchlan <scott_at_isd.canberra.edu.au>
Date: Tue Nov 10 16:48:33 1998

At 00:46 10/11/98 -0500, Ethan Dicks <erd_at_infinet.com> wrote:

>> > The problem with replicating the SuperElf is the keyboard. I have no
>> > idea where to get that chip from (74941?), nor an inexpensive source
>> > for that many pushbuttons (including some latching ones).

[Snip]

>If you'd seen the Elf-II schematic, I don't think you would have responded
>that way. I was never suggesting cannibalizing AT keyboards. They are
>entirely unsuitable. The original Elf-II has a keypad built up from
>individual pushbutton key switches, including several ones that latch
>up and down for LOAD, RUN and MEM PROT. The hex digits are latched
>through a (then) standard keyboard encoder chip.

[Snip]

>I was suggesting finding modern parts from a distributor of new or
>recycled (surplused) parts. I further suggested that modern replacements
>could run as much as $2 or $3 per switch (20 switches - 0 to F, R, L, P
>and I).

As far as the keyboard encoder chip goes, you wouldn't be thinking of the
74922 would you? It's a 16 key keyboard encoder chip designed, as I
remember, to encode a 4 x 4 key matrix. Or perhaps the 74923, a 20 key
keyboard encoder (which uses a 5 x 4 key matrix). If some of the non-hex
keys latch the 74922 would be more suitable, because I'm pretty sure both
these chips can only recognise one key being pressed at a time.

Anyway, according to the Australian edition of the Farnell catalogue, both
these chips are still available. Farnell wants $A20.48 each for the 74C922
and $A20.52 each for the 74C923 (plus 22% sales tax) in quantities less
than 25, and $A14.11 each for the 74C922 and $A14.37 each for the 74C923
(plus tax) in quantities between 25 and 100. However, Farnell is usually
the most expensive place to buy components, so I'm sure you'll be able to
find them somewhere cheaper (for example, an Australian company called
Altronics stocks the 74C922 for $A12.95 each in quantities less than ten,
and $A12.50 each for ten or more *including tax*).

As far as the keys go, the momentary action (i.e. to 0-F) keys shouldn't be
a problem. PCB mount NO push buttons (I think they're called D6 type)
switches are available for $A1 each in small quantities. Alternatively you
could use a hex keypad. Farnell lists one for $A14.72 (plus tax) in small
quantities, so once again I'm sure you could find one even cheaper. That
would only leave four of the relatively expensive latching switches to buy.

Depending on the price, I'd probably be interested in one of these little
machines too.

Regards,

| Scott McLauchlan |E-Mail: scott_at_cts.canberra.edu.au |
| Network Services Team |Phone : +61 2 6201 5544 (Ext.5544)|
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Received on Tue Nov 10 1998 - 16:48:33 GMT