My origional Orac had a small analog circuit that emulated the hum of the TV Orac. The clever addition of a high-farad capacitor behind the frequency-drive circuit even allowed me to get the start-up pulse sound right, though I was never able to simulate the power-down sound in this manner to my satisfaction.
The Arduino Microcontroller's audio-modulation capabilities should enable me to get all of this right in the new model. Of course in a real stage-prop, the sound effects wouldn't be built in anyway - they would be added in post-production. But this project is as much about demonstrating things to do with the Arduino, and the whole thing is more impressive in live demo with sound!
I stuck a piezo transducer (top right) between one of the output pins and GND and used the
tone(pin, Hz, [duration]) command to drive it. An Arduino only supports one sound channel, though you can send it to any output pin. Also, I found the tone command does weird things for a frequency below 30Hz so I avoid setting the frequency below this.
Here is the start sound, which is an initial higher-pitch pulse which then rapidly drops to the running hum:
Here is the running sound, which is a low-pitch hum with slight, random pitch variations:
And here is the shut-down sound, in which the running-hum tails down in pitch, with some significant random pitch variation:
They are not brilliant replications of the TV Orac's sound, but are close enough for my demonstration purposes.
I replaced the Peizo Transducer on the sound output with a tiny little speaker from a smashed mobile phone I found on the road (right). The sound is suddenly AMAZING!!! Loud and clear is the exact expression.
Next: The Key