On Tue, 22 Jun 2004 10:31:00 +0100 "Hans Summers"
wrote:

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 ;-)

Over here you can sometimes buy those little stick-on digital clocks,
made for sticking to your bathroom mirror. They cost about $3 and
include a crystal, a display, and a battery, plus all the circuitry to
make them work together.

I think their exact frequency is 32,768 (= 2**15) Hz, so that dividing
by 2, 15 times will count seconds. If this will work for you then
buying one of them might be a very cost effective way to pick one up
easily. If you can't find one there, I think I have one which I
salvaged out of a dead watch.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

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

"Paul_Morphy" wrote in message
...
If this Mouser part will work, you won't have to deal with a minimum
order.


http://www.mouser.com/index.cfm?hand..._pcodeid=69500

In case the link doesn't work, it's Mouser Part #: 695-CFV206-32K . 32
kHz, 12.5 pF.

Thanks Paul, I'm looking into this and a couple other alternatives.

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

========
Hans , May I suggest you check supply of above with Mode
Components -Birmingham, small company (no VAT)

www.modecomponents.co.uk

I checked Frank, they don't sell 32KHz. Only 32.768, and I have loads of
those falling out of my junk box already!

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

I think their exact frequency is 32,768 (= 2**15) Hz, so that dividing
by 2, 15 times will count seconds. If this will work for you then
buying one of them might be a very cost effective way to pick one up
easily. If you can't find one there, I think I have one which I
salvaged out of a dead watch.

Thanks for the offer Jim, I have quite a few of those crystals already, but
they aren't suitable for this application which requires 32KHz not 32.768.

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