IBM Factory Clock

A GPO Master Clock (Clock 36) would not be suitable as it doesn't provide 60 second pulses

My Magneta version has a 60 second pulse unit, that drives the 60 second dial on the case (which I leave on GMT just to confuse visitors), the other unit is a 30 second one driving the house clocks. There where many different "counters" for PO 36 clocks. A favourite for exchanges was 6 seconds for the call cost counters.

[M0FYA Andy]

Is your Magneta a Magneta-made PO36 or a Magneta M37 on which the PO36 was based? I also have an M37 with a 60-second set of contacts.

Andy

[Paul Stenning]

Originally Posted by Nickthedentist

...or a quartz clock mechanism with the seconds hand operating an optointerruptor.

I like this idea, because it is simple and low tech. You do actually have a master clock (albeit a battery powered quartz movement) driving the slave clock too.

Also these movements are a good way of getting accurate low cost mechanical timekeeping. I have seen them used in things like cat feeders for exactly that purpose.

An opto-interruptor (make a double-ended second hand for 30 seconds), a power transistor or relay with a bit of other electronics, and a spare power supply or battery, and it shouldn't cost more than a tenner or so. You can buy a cheap clock in Ikea, a pound shop or charity shop just for the mechanism and second hand.

[Refugee]

If you are going to butcher anything I would go for the quartz movement.
It would not be difficult to make a divide by 30/60 circuit with a couple of chips.
You will then have 4 wires and the ability to use either type of slave clock.

[Radio Wrangler]

Or use two optointerrupters with a single second hand, if you finf that easier than making a new hand.

There are so many ways of doing this, that you have to pick something which best fits your tastes, abilities and what you have to hand.

Sometimes, when confronted with too many things to choose from, I can be stopped in my tracks for an embarrassing amount of time.

David

Andy, here is the nameplate...