"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?

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 .

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.

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 ;-)

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