Slightly OT: Digital watch circuits

[Theo Markettos]

GaborSzakacs <gabor@alacron.com> wrote:

It seems that this model (produced only in small quantity) did not have
a custom chip (article quotes 25 chips in the watch). It had a button
to illuminate the display and two magnet-activated switches to set the
time (hours and minutes). Modern digital alarm clocks still use the
same clunky Hour and Minute buttons to set time, which is very
frustrating when you want to move the time back by one minute or one
hour.

There's some pictures of the mechanism here:
http://www.timetrafficker.com/private/pulsar-p1-25-chip-module/

What's interesting is the modern-looking SMD construction, with gold tracks
on a ceramic substrate. The LEDs use discrete bond wires but all the chips
are in 12/14 pin ceramic packages, of roughly MSOP size.

Each of the 25 chips is lettered. There are 5 As, 5 Ks, 5 Gs, 3 Cs, and one
each of BDEFHIL - looking at the layout it's possible to infer something
about their function.

I wonder if they're 74- or more likely 4000-series in custom packages?

Theo

 

[Kevin Neilson]

There's some pictures of the mechanism here:
http://www.timetrafficker.com/private/pulsar-p1-25-chip-module/

I was wondering what the glass tubes underneath the circuit board were--they look like the inside of reed relays. Then I realized that's exactly what they are. They're the switches used for setting the time, activated with an external magnet.