Saturday, 19 May 2018

Synchronised Westerstrand Impulse clock driver.

A while ago, a friend, Alex, asked me how he could drive a synchronised clock he had procured.

It was a Westerstrand clock. The sort that you used to find in factories, offices and schools. It's an electo-mechanical driver, driving a conventional clock display. It doesn't posses any time keeping mechanism.

Now Westerstand are still alive, well and trading since 1906. Their website is here.

Anyway, according to some information gleaned from their website (they still make these things) the clock needs a pulse of 24 volts alternating in polarity to advance a minute. 

I quickly drew up a small circuit, with an arduino and a GPS receiver to drive Alex's clock.... he pronounced it too complicated, and removed his electro-mechnical movement and fitted a quartz clock movement .....

.... that's cheating.

I managed to procure the same clock movement in somewhat distressed condition, and managed to put it all back together.

So what about that proper driver? Good plan. I ditched the GPS receiver, as I have the GPS master clock, and added a 433 MHz receiver to receive the signals.

The clock will "free-run" after being set, using the 490Hz interrupt driven clock, as previously seen on the Arduino analogue clock.

Pulses are sent to the clock by using a small H-bridge.

Now the electronics has no method of knowing where the clock movement is, so before the synchronising signal from the GPS master clock is received, the clock needs to be set to 12 o'clock. I've added a minute and hour button to the PCB to allow the movement to be set.

The code also automatically adjusts for British summer time.

A board is designed...


... and turned into reality.

Code and eagle files can be found on my github page at

Here's a video of it in action...

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