10 Aug
2004
10 Aug
'04
3:40 a.m.
On 8 Aug 2004 at 21:42, Tony Duell wrote:
So the LED is dark if the machine is off, on steadily
if the machine
is on and no error (555 is held reset, so the output is low all the
time), and blinks (controlled by the 555) if there's an error.
The chief electrical engineer at our company in the 1980s was a fellow who
excelled at making components in his designs do two or three jobs each.
It's an artistry that HP displayed, as you indicate.
I can't easily reproduce the schematic in
ascii-art, and I don't have
a scanner, but if anyone is seriously interested I will see what can
be done.
The schematic for the HP 64000 circuit appears on page 8-41 of:
http://www.bitsavers.org/pdf/hp/64000/64100-90910_64100svc_Dec83.pdf
...and it's described on page 8-13.
-- Dave