Details of my xylophone playing clock

 

This picture shows the mechanism moving the clock's hands.

To the left you can see two solenoids (electric magnets), one for the minutes hand, one for the hours hand. Above and partly inside the solenoids are two metal rods that are pulled down into the solenoids when a current is applied. On the top there are two balance arms that are tilted when the magnets are activated. To the right there are two water filled bottles. Inside the bottles there are discs almost filling the cross section of the bottles. They hang in thin threads from the balance arms and serve as shock absorbers. Each time a magnet is activated, a steel wire arm hanging from the balance advances a cogwheel 1/60 of a revolution.
 

 
 

This picture shows the interior of the xylophone playing mechanism.

Below each metal bar you can see a solenoid. When an electric current is applied to it, a small metal rod is pulled up into the solenoid. It hits the Xylophone bar on top of the solenoid. You can see some of the metal rods as they rest on the felt mat.
 

 
 

 This picture shows the electronics assembly


 Technical details

Xylophone 12 notes, C to g. Halftones are missing, and this is a pity. Transposing music into the limited 1 1/2 octave would have been much easier with half-tones. If I were to build it now, I would have chosen a two octave chromatic xylophone.
Xylophone solenoids Several hundred turns of thin lacquered copper wire (from an old loudspeaker magnet) wound on a paper coil with cardboard discs to constrain the wire. Resistance 18 ohms. Driven from 7.5V. Each pulse lasts about 15 ms. Metal rod inside solenoid: diameter 1.2 mm, length 20 mm. 
Clock solenoids Several hundred turns of thin lacquered copper wire (from an old loudspeaker magnet) wound on a glass tube with cardboard discs to constrain the wire. Resistance 27 ohms. Driven from 7.5V. Each pulse lasts about 1s. Metal rod inside solenoid: diameter 3 mm, length 5 cm. 
Balance arms Length 7 cm to each side. Extra weight on the right side.
Cogwheels Diameter 85 mm, 60 teeth. Made of tin can lids, cut out with a pair of scissors. Braked by spring operated aluminium arms that push on each side of the cogwheels.
Hydraulic shock 
absorbers
Glass bottles. Diameter 25 mm, height 50 mm. Filled with water. I have added lubricating oil and dishwashing detergent to avoid algae growth and evaporation. A plastic disc inside has almost the same cross section as the bottle, serves as the shock absorber and moves up and down in the bottle. It is weighted down with aluminium disks to ensure that it rests on the bottom and stays horizontal.
Electronics Microcontroller Philips 87C752, 12 MHz. Development tools: DS-750 from Ceibo. Assembler code. Program size 350 byte. The 22 tunes entered so far require 950 bytes of storage (1 byte per tone [4 bit time since last note and 4 bit note identification]). Chords are played serially since the power supply cannot drive more than one magnet at a time
Adjusting the clock There is no electronic feedback from the hands to the electronics. The user must adjust the hands to the position of the electronics manually. A three button user interface works as follows: 
 
Button 1 pressed Advance electronics to next minute. (Step minutes hand)
Button 2 pressed Advance electronics to next 12 minute position. (A hours hand step is 12 minutes. Step both hands)
Button 3 pressed Advance electronics to next hour. (Play hours chord and step both hands)
Button 1 and 2 pressed Play next tune. (Do not advance electronic clock or step hands)
Button 2 and 3 pressed Backwards adjust. 60 s to next hand movement.
Button 1, 2 and 3 pressed Clock reset. Starts at 1 and plays 1 o'clock chord (C-D)
 

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Last modified 03.06.98