musical doorbell - variations on an old theme

variations on an old theme Although we would not like to make a habit of it, going back to an old design when new components become available is sometimes very rewarding. And so it is in this case of the musical doorbell with the in- troduction of a new IC, or rather quartet of ICs, the UM 3481/82/83/ 84 series. As could be expected, the principal part of the circuit is contained in the IC: oscillator, frequency divider, drive ROM, a ROM with 512 musical notes, tone generator, rhythm generator, timbre generator, modulator, run-off control, and pre-amplifier. Apart from the IC, the circuit com- prises an a.c. operated power supply with voltage regulator, a push-pull amplifier for driving the loudspeaker, and a number of associated components. Resistors R1, R2, potentiometer P2, and capacitor C2 are the frequency- determining elements for the on-chip oscillator. Preset P2 is for adjusting the run-off speed, that is, the speed at which the tune is played. Resistor R7 and capacitor C4...