Just a couple of suggestions for those considering using calculators for
event counting.  I haven't tried it, so please don't have a go at me if it
doesn't work or can't work.

1. Auto-defeat of auto-off (1).  Using a very slow clock (don't ask me
where it comes from) with a period approximately that of the auto-off
timer, add 1 on every +ve edge, subtract 1 on every -ve edge.  Only take
readings while this clock is low.

2. Auto-defeat of auto-off (2).  Using the same clock as in 1, activate
"M+" on +ve edges, "M-" on -ve edges.

3. Add built-in timing at the same time as auto-off defeat.  Use a stable
clock with period well below that of the auto-off, but some nice round
figure like 2 minutes.  On every +ve clock edge swap memory and display,
add 1 to display, swap memory and display.  This gives event count in
display, elapsed time in memory.  (Avoid event increments near +ve clock
edge.)

4. Make auto-off irrelevant.  My calculator's "memory" register is
non-volatile.  Therefore, event counting only requires: "AC/On" to turn the
calculator on, "1", "M+" and then into sleep mode.  I've no idea what the
calculator's current drain is - it's one of those which runs off solar
cells, with no battery at all.


Tim Forcer               tmf@ecs.soton.ac.uk
Department of Electronics & Computer Science
The University of Southampton, UK

The University is not responsible for my opinions