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The Mesmeriser

A LED clock with a difference

Design by Scott Melling*
*Grantronics Pty Ltd.

Have you even been accused of being a clock-watcher? Whether you have or not, there is a definite risk of being entranced (enchanted?) with this new LED digital clock. You tend to ignore the central 4-digit display and just concentrate on that magical circular LED performance.

At the beginning of each minute, each successive LED races anti-clockwise around the periphery to take up its position as the seconds count builds up. As the seconds count nears 30, each new LED only has to traverse half the circle and so each LED makes its circuit slightly slower than the last until finally, as the count approaches 60, the last few LEDs make the transit very slowly indeed. But each LED transit around the circle, whether it covers the whole 360° or just a few, takes exactly one second.

Click for larger image
The LED clock comes as a complete kit of parts and includes a double-sided plated-through PC board with a solder mask and silk-screened overlay.

So you find yourself wondering: just what fancy machinations have been pulled to achieve that? The answer is, of course, that there is a fancy microcontroller calling all the shots. But even knowing that and having considered all the programming that must have gone into it, you still tend to sit there mesmerised by this clock. You just have to see it but be warned – when you do, you will probably want one!

Apart from that magic circular LED array, this wall clock also has a 4-digit readout with 12 or 24-hour operation. It also features an alarm with piezo sound and opto output, a battery backup for time-keeping and alarm functions, AC mains synchronisation and crystal timebase for precise timing, an efficient switchmode supply powered by a 12V AC plugpack and a high quality double-sided, screen-printed and solder-masked PC board with plated-through holes. What more could you want?

The hours and minutes display consists of the four large digits in the centre of the clock face. It can be set to display either 12 or 24-hour time, depending on the position of a single jumper link (JP1). On the righthand side of the minutes digits is an AM/PM indicator LED and this is active for PM hours if the 12-hour display mode is chosen.

The timing uses a crystal oscillator for short term accuracy with the chaser control and is synchronised to the mains AC cycles when present for long term accuracy.

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