Many thanks Tim. I didn't realise 32KHz crystals were available. The
usual
32768 wouldn't give the right timing but 32KHz is perfect. You actually
prototyped this and measured the current? Did this use an old 4060 or a
74HC4060? What's the difference betweem families in terms of current
consumption? Also, how do these families compare to things like 74AC,
74ACT,
74HCT? I know the T means TTL-compatible levels rather than the old CMOS
family compatible levels, but is the current consumption different too?

Normally I resist the urge to prototype things, but yesterday was slow
and I could do this whole thing on a proto-board. I used a 4060, not a
74xCxxxx device. I have no idea how it'd play out on a xx4060, but with
a 74HC04 and the watch crystal I was seeing 1.6mA, and with the 4060 I
was seeing 32uA. This is an unfair test, because you're supposed to use
the 74HCU04 for oscillators; I have no idea how much this affected
things. I _did_ notice with the 74HC04 that running it at about 3V
brought the current down to the 30-50uA region, however.

Ok thanks Tim, 32uA is great. I will stay with a 4060, I don't want to add
an extra IC just for the oscillator (e.g. 74HCU04).

Loads of questions I know. But this is fantastic as it will enable me to
reduce the current consumption of the thing to under 1.5mA. I hope I'm
right
in thinking that by replacing the LED switching transistor with a FET,
I'll
also save some current consumption because of eliminating the
base-emitter
current, but I'm not a FET expert.

It should save a bit, but with a good junction transistor you should
only have to apply about 2-5% of the collector current to the base to
get saturation. If you're using one of the old standbys you should look
at newer transistors -- Zetex is good for this.

I was using a BC547. I'll look into a better alternative.

Thanks again

73 Hans G0UPL
http://www.HansSummers.com