To use the watch movement as a timer the battery can be removed and the
battery terminals connected to a pair of wires that will feed the watch
1.5 volts to start the timer. The problem is how to stop the
timer. For example if the crystal is shorted out the LCD goes
When the crystal is shorted the LCD goes blank, BUT when the short is
removed the LCD resumes the prior count. This means the cheap
watch CAN be used as a timer good for up to one year.
For a timer that will be good for up to 24 hours, many days if you
manually keep track of the days, you can use an analog quartz
watch. I found one for $8 at the local Big Lots store.
That's eight times more than the price of the digital watch that
included time and date functions. If that was built into a
product there's a large impact on the selling price.
The LCD might be removed from the rest of the movement. More needs to be done to understand how to drive the LCD.
There are 13 contacts on the PCB which connect to the glass using a zebra strip.
Contacts No. 1 and No. 13 both have a signal that has three levels:
+150 mv, 0, -150 mv. The time between transitions is about 100 uS.
All the other contacts (No. 2 through No. 12) have signals that switch between +150 mv and -150 mv.
The LCD glass is specifically made to be a watch 12 hour time
display. This means the tens of hours digit can only be "1" or
blank. Notice that the "1" in the time display above
is right aginst the left edge of the glass, i.e. there is not room for
more segments like would be needed to display a "2". In a similar way
the tens of minutes digit can only be blank, 1, 2, 3, 4 or 5.
This reduces the number of segments that need to be controlled to 22
which matches the use of two control and 11 segment contacts.