Ancient and modern techniques display timely brilliance on a grand scale!

Portuguese reader Fernando Bentes de Jesus emailed us during the Autumn of 2002, saying that his favourite electronically-controlled wall clock had “ticked its last tock” and that it could not be revived. He asked if we knew of anyone who might be interested to design a replacement.

Questioning him further, he explained that in essence his “dream clock” consisted of 60 light emitting diodes, arranged in a circle having a diameter of 24 centimetres, and displayed the seconds count. In the centre were eight digits with each segment comprised of several l.e.d.s. These displayed hours, minutes and calendar information. Thinking about the possibility of designing a clock along these lines, the author became intrigued by the thought of designing one that embraced both old and new technologies - old in the form of l.e.d.s for the display rather than a liquid crystal screen, and new in the form of a PIC microcontroller (inevitably!).

Key features of this project are:

• Crystal controlled
• Circular display having diameter of 9·8 inches (250mm)
• Inner ring of 60 l.e.d.s displaying both seconds and minutes
• Outer ring of 12 l.e.d.s displaying hours in conventional (analogue) 12-hour format
• Inner zone of 100 l.e.d.s in 4-digit 7-segment numerical format, cyclically displaying hours (24-hour format) and minutes, months and days of month, and temperature in degrees Celsius to one decimal place
• Three switches provide adjustment for all display values, and for the precise calibration of the timing accuracy to compensate for normal manufacturing tolerance in the controlling crystal’s oscillating rate
• Powered at 9V to 12V DC via a mains supply adaptor, with battery back-up
• Current consumption only 65mA (thanks to heavy multiplexing of LEDs)
• Adjustable brilliance of the LED numerals to suit personal taste