Music Centre

The automatic reproduction of music can be traced back as far as the 14th century, when Flanders introduced a mechanical bell-ringer controlled by a rotating cylinder. Similar designs appeared in barrel organs (15th century), musical clocks (1598), barrel pianos (1805), and musical boxes (1815). All of these machines could play stored music, but they could not play arbitrary sounds, could not record a live performance, and were limited by the physical size of the medium. The first device that could record sound mechanically (but could not play it back) was the phonautograph, developed in 1857 by Edouard-Leon Scott.

The player piano, first demonstrated in 1876, used a punched paper scroll that could store an arbitrarily long piece of music. This piano roll which first had 58 holes, was expanded to 65 and then was upgraded to 88 holes (generally, one for each piano key). When a perforation passed over the hole, the note sounded. Piano rolls were the first stored music medium that could be mass-produced, although the hardware to play them was much too expensive for personal use. Technology to record a live performance onto a piano roll was not developed until 1904. Piano rolls have been in continuous mass production since around 1898.

UNIT 16

Time to Dust Indicator

I thought about this circuit when I heard that a lot cleaning personal in hotels were either in dusting rooms more often than necessary or not enough. I have not yet built and tested this circuit completely but in concept it should work. The circuit draws very low current from a +3v battery and could be housed in a package similar to a small ashtray. The assembly might be placed in a suitable out of the way area to collect dust. It would alert a maid when it was time to dust the room. The circuit detects dust with an infrared LED that is pulsed so its light shines onto a smooth flat plate. Any dust settling onto the surface is detected by a phototransistor, mounted at a 90 degree angle from the LED. When the dust reaches a particular level, sufficient light is reflected into the phototransistor to change the logic state of the circuit to an alarm condition. The alarm output could be connected to a beeper, a flashing LED or to one of the LED flashing circuits in this hobby circuit section.

UNIT 17

Using the Morse code

The main use of the Morse code these days is within ham radio or amateur radio. When using the Morse code, widespread use is made of abbreviations and codes. While this may make any messages difficult to decipher for a newcomer to ham radio, the codes are quickly learned and their value recognised. They provide a very powerful means of communicating quickly and concisely. By using them it is often found that actual information can be sent almost as quickly as if it was sent via the spoken word. The use of the codes, forces a much more concise form of communication apart from allowing fewer letters to be sent. The other advantage of using these codes is that they enable ham radio operators who may not be able to speak English to be able to communicate with a much wider number of people. By using the codes it is possible to communicate with other ham radio stations quite easily with only a minimal knowledge of English.

Morse may not seem to be the latest in technology, and it could never be argued that it is such. However it still has many advantages within ham radio even in today's high tech world.