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This
tiny circuit comprising of a single 3 terminal IC UM66 can be
built small enough to be placed inside a greeting card and
operated off a single 3V flat button cell.
There is not much to the circuit. The UM66 is connected to its
supply and its output fed to a transistor for amplification. You
can either use a 4ohm speaker or a " flat" piezoelectric tweeter
like the one found in alarm wrist watches.
If you use the piezo, then it can be connected directly between
the output pin 1 and ground pin 3 without the transistor.
The UM66 looks like a transistor with 3 terminals. It is a
complete miniature tone generator with a ROM of 64 notes,
oscillator and a preamplifier. When it first came into market, it
was programmed for the "Jingle bells" tune. Now they come with a
wide variety of different tunes.
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