Details of the ball clock at "Vitensenteret",

the Science Centre and Exploratorium in Trondheim, Norway.

  This page describes details, you find the introduction and main picture here.


This picture shows the fan arrangement.

The fan case is made out of 7 mm plywood, with plastic front. The fan is an old circular fan of the type used in PCs, but more powerful than what is usual today. All ball passages are made to fit the balls quite closely. A diameter of 40 mm is suitable. Note also the following details:  

This picture shows the three uppermost ball trays

Just before this picture was taken, tray one was filled. It tilted, and after it emptied and tilted back, one of its balls rolled onto tray two. Tray two also became full, and has just started tilting. The balls have not started rolling yet, but they soon will. The first ball will stop on the rails on the left side of tray three. The next balls will roll over it and fall down into the reservoir. When the tray is empty, it will tilt back and the first ball that rolled off it, will roll onto the third tray. Note also the following details:


This picture shows the ball reservoir

When the photo was taken, the reservoir was less than half full. When full, it will be filled all the way up to the upper left corner.

Technical details

Total size Width of case 75 cm. Height of case 80 cm (excluding tube extending above case) 
Trays Minutes trays room 2, 5 and 6 balls and count to 60. Hours trays room 4 and 6 balls and count to 24.
Balls Standard ping pong balls. 24 balls are needed (1 + 4 + 6 + 3 + 5 + 5 extra in fan module)
Fan Old electronics cooling fan. Rated 115 VAC, 0.22 A. More powerful than PC power supply fans. A 75 W 230 V light bulb in series adapts to 230 V.
Building material Lego Tecnic, about 1000 standard parts. Vertical tubes are of plexiglass, 40 mm inner diameter. Case is made of aluminum and 3 mm plexiglass.
Electronics The electronics is visible on the same picture as the fan arrangement. You can see the circuit board which is mounted with all the components visible. Microchip PIC16C84 microcontroller. Development tools MPASM assembler from Microchip. Homemade programmer using design and program made by Jens Dyekjær Madsen. Program size: 80 program words. Ordinary AC/DC adapter from 230V AC to 5V DC. Electronic opto-coupled relay interfaces to mains voltage driving fan.
User control There is a button which viewers can press when a light emitting diode is on. Every "one minute time window" there there is a "50 second time window" in which a button press will start the fan. If no one has pressed the button within the "50 second time window", the fan starts automatically. I believe the possibility to affect the clock behaviour makes the clock more interesting to children (and maybe to adults also). 
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 Last modified 03.06.98