old clocks

Many slave clock systems had the dials in series as you describe (and as is described in Hope-Jones's book), but I am sure the system we had at school (which weas almost certainly from Gents of Leicester) had the slave dials in parallel and fed them 24V pulses. I deducdd the first fact by unpluging the connector on one of the slaved and finding it had no effect on any of the others and the latter by useing a 'scope... Anyway, the pulses for that system were alternate polarity pulses, one pulse per minute. Something like this : -- -- | | | | -- ------ ------ ------ -- | | | | -- -- | | | | <-1min-> The slave clock motor was similar in concept to the motors in those quartz insert movements. It had 2 mechncially stable positions half a turn apart. The +ve goign pulse pulled the (magnetised rotor) one way round between the ends of the coil core, when the pulse ended, the rotor moved ot the nearest mechanically stable position. The next pulse (of the oppostie polarity) again lined the rotor up with the coil core, but the other way round, It then moved to the other stable position. And so on. The master clock had a spring-drivien mechancial movement with a short (about 30cm) pendulum. The spring was automatically rewound my an electric motor, and would keep the clock running for quite a time (12 hours or more) if the mains failed. The pulses to the slave dials were generated by a pair of 3-terminal mercury switches, which were rocked by a camshaft. Power to the switches (and thus the slave dials) came from a transofmer/rectifier unit. Of course if the mains failed, no pulses were gneerated (there was no battery backup) and the slave dials didn't move. However therew was a mechanism invovling a mains motor and a differneital gear which kept track of the missing pulses (when the mains motor wasn't turnign). When the mains came back on, the thing 'caught up' generating pulses every few seconds to reset the slaves to the correct time, Anyway.... While it would be nice to have such a master clock (or, indeed one of the synchonomes), these slave dials (in all the common systems) effectively count electrical pulses. And it doesn't matter how you genrate the pulses. Provided you know what the pulses should look like (voltage, current, whether they have to be of alternating polarity), it's a fund exercise to design a digital circuti to produce them using your favourite technology, whether that's TTL, FPGAs or microcontrollers. -tony