Make an Atom Synchronised Clock from a 1950s Slave Dial using Arduino

Posted on Feb 5, 2014

When I purchased the salve dial, it came with no instructions, packaging or other details. The only markings (other than five decades of grime) were those on the face (SMITH SECTRIC, ACELEC SYDNEY), and some markings on bracket holding the mechanism together (E. C. S. 205/19 MADE IN ENGLAND). There were markings on the coil, but they were too faint

Make an Atom Synchronised Clock from a 1950s Slave Dial using Arduino

Click here to download the full size of the above Circuit.

to read. In order to drive the mechanism, I needed to know how much voltage had to be applied to the coil to reliably advance the hands, for how long, and how many seconds the hands would advance for each pulse. I was concerned about overdriving (and hence damaging) the coil, but also concerned about under-driving it, resulting in an unreliable movement. I was able to find some general information on these units on the web (thanks to Google ). My thanks to the people who put together the English Clock Systems website. It turns out that most such clocks would advance either 30 or 60 seconds depending on the model. The mechanism was specified as a combined resistance of around 3. 5 ohms, and a current rating of 0. 3 amps, for an operating voltage of 1. 05 volts. IN reality, most such units were driven by banks of old dry-cell batteries with a voltage of 1. 5 volts, so that is what I aimed for. Note that slave dials such as this typically had a shunt resister is parallel with the coil. The reason for this was so because these clocks were often wired in series. Without the resister, if the coil on one clock went open circuit, all the clocks would stop working. The circuit needs to be able to drive the clock`s coil at 1. 5 volts are there-abouts. I`m sure there are more elegant solutions, but I simply used a variable regulator (an LM317) to supply the voltage, and a the output from this is switched via a transistor (TIP31)....

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