getting 1 hz pulse of a wall clock movement


Joined Apr 5, 2008

That depends on how the wall clock is made.
Many use a 32768 Hz crystal.
Find the signal, amplify it and divide it by 32768 and you will have your 1 Hz timebase.



Joined Sep 10, 2007
You can count a 16 bit word with it starting from 0x8000, and when it overflows, that’s your 1 Hz interrupt.


Joined Jun 19, 2012
If your clock is AC powered, divide the line frequency by 50 / 60 and you got it.

The long term accuracy will be better than any crystal oscillator.


Joined Nov 23, 2012
Can I get the 1 hz pulse out of a wall clock movement to time a digital clock?
If you are talking about the type pictured below and usually available on a clock available from Goodwill or Savers stores as used for $1 to $3, absolutely!

Accuracy may be off 1 or 2 seconds per day but pretty darn good for most applications. Nice strong pulse every second to power the solenoid (usually a gold-tone silicon-steel plate with an eyelet to rachet the gears of the clock mechanism. You can just tap into the non-grounded lead of the solenoid's coil and connect our circuit's ground to the clock ground. It is likely easiest to keep the clock's battery on the clock instead of using system power for the clock.

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Joined Dec 19, 2007
Per GopherT's suggestion, I've used gutted 1.5V battery clocks for 1Hz clocking. Some wall/desk clock use pullup on the coil outputs. Some use pulldown. Attached are two configurations I've used.


1 Second Clock.gif 1 Sec Clock.jpg