Robert Monsen said:
If you need accuracy, I'd think about using a watch crystal, or even the
60Hz powerline (which is by some accounts kept accurate by an atomic clock.)
Jan
Some years ago - about 1974 - I made a clock using the utility supply (50Hz
here in UK).
I picked off an AC signal of about 6vrms, fed it through a diode, through a
1K resistor to the top of a 4v7 zener. Other side of zener to 0V. Across
the zener was a 100pF (I think) small capacitor to catch spikes.
The signal then went to a 74LS14 schmitt inverter. The output was a nice
clean 50Hz pulse train.
Putting that through two 7490's resulted in a 1Hz clock pulse for the main
clock circuit.
The fun part was putting the LED displays in a small box, with all the rest
of the circuitry on a cable (hidden at the back of the bedside table).
People thought it was a lovely small clock!
An touch sensitive alarm switch comprised a piece of veroboard with
alternate strips connected so that when I put my finger across some, it
switched a cmos gate - only need a microamp or so to pull down a 500K pullup
resistor.
The alarm was a 74132 quad schmitt nand connected as two oscillators, one at
about 2hz, the other at a nice screechy tone. Gated one into the other, and
conctrolled by clock alarm output and touch switch. Output via transistor
to smal speaker. Woke me up a treat for years.
hth
Neil