Arduino Uno

light sensor

Corner
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Tone generator

Warning: do not connect immediately to some input device as the voltage output by the Arduino may damage it!

Schematics

For this circuit, I've used an old PC-speaker.

tone generator schematics

To mix the output of the signals to output to a single speaker, simply use a resistor from each output pin and tie them together at the speaker. The volume depends of course on the resistor used.

Photo

tone generator

Links

 Arduino Tone Library