Hans Summers wrote:

"Tim Wescott" wrote in message
...

Hans Summers wrote:

A 4060, using National's recommended circuit (from an '80 databook) and
a 32768Hz watch crystal, pulls 32 microamp -- and like I said before,
Digi-Key has 32000Hz crystals in stock, so there's your 1kHz reference.


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.

What exact circuit is in your '80 databook? I just had a look at various
datasheets from different manufacturers, and all seem to have the same
configuration. The national datasheet for the 4060 shows values of 15M and
330K for the resistors to suit a watch crystal
http://cache.national.com/ds/CD/CD4020BC.pdf . I also found this 74HC4060
datasheet for the ON Semiconductor version. It includes an interesting
treatment of the calculation of the resistor values, see
http://www.farnell.com/datasheets/42247.pdf .

Your National datasheet matches the one in my databook.

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.

Another nice thing is the 32KHz crystals are physically tiny: 6mm long and
2mm diameter. This means if I use SMD IC's I can make a next generation
counter a fraction the size of the current one which is already miniature.
One problem remains, which is getting hold of a 32KHz crystal. I have never
bought anything from Digikey. The part I need is XC972-ND and is priced (UK
pounds) £0.47. However I notice that there is a £10 handling fee and £12
shipping! The total order cost would be £22.47, for one simple crystal.
That's about US $41! Therefore does anyone in rec.radio.amateur.homebrew
reside in the US, order frequently or in the near future from Digikey, and
wouldn't mind adding one of those to their order and popping it in an
envelope to me - I'll pay all costs of course as long as you don't charge me
£10 handling ;-)

The handling fee ($20 in the US) is only applied for small orders, so
you can either get $1.00 worth of stuff for $21, or you can get $21
worth of stuff for $21 -- this still doesn't save you the shipping
charges, though.

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




--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com