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GPO 36 master clock contact impulse debouncer 2011-06-17

GPO 36 master clock contact de-bouncer

I decided to build this circuit after my Gents GPO 36 master clock started having the odd extra pulse bounce and occasional pulse miss as well, which caused the slave dials to get out of step.
As I was aware that the 30 seconds output contact is not supposed to driving the slave clocks directly, although the setup was like this in my GPO 36 master clock for the pilot dial fitted in the door.
Attached schematic will show the components and I set up the capacitor time constant to about 1 second.
It doesn’t matter if the clock pulse is shorter than ½ second or bounces twice when the pendulum pushes the ratchet through the 30 seconds lower cog of the count wheel.
It will give a 1 second impulse.
The circuit is very compact in use and can easily be fitted in the clock housing.

The circled numbers in the attached circuit refer to the top connectors of the GPO master clock.
To note is that I changed the polarity of the clock supply to be able to use a NPN darlington transistor.

Clock contact row

3—30 sec impulse to D1
5—Positive 12 Volts dc
7—pendulum drive
8—to slave dials

Another beauty of this simple circuit is that it is perfect to be used for synchronising another pendulum clock(s).
The “slave” pendulum clock requires a piece of soft steel/iron to be attached below the bob to be attracted by the electromagnet.
It will require it’s own circuit but the materials cost virtually nothing anyway.
I have a ¾ seconds Bürk pendulum master clock being “locked in”, with the 30 seconds impulse from the Gents 1/1 seconds master.
I set the time constant to about ½ second and drive a 47 ohm coil which attracts the pendulum at the end of the swing.

I got both clocks running in perfect synch via a 30 metre long cable as the “slave” pendulum clock is in the workshop in my garage.


5052 is the circuit in the GPO
5053 are the top terminals of the GPO
5055 is the second circuit driving the “slave” pendulum
5058 is the iron slug under the slave pendulum.

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