8 Aug
2004
8 Aug
'04
9:41 p.m.
ard(a)p850ug1.demon.co.uk (Tony Duell) wrote:
Talking of HP using 555 timers, they used one to drive
the power-on light
in the HP86 (and I assuem the HP97). [...]
(nitpicking here, you are talking about
the 87)
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.
Actually the LED blinks when the machine is busy (e.g. running a program).
This is very neat as with the HP85 you sometimes do not know whether the
program has finished or is still running.
**vp