This puzzle was a lot of fun, which is probably why I didn’t take a huge amount of photos during its construction, I was too immersed in making it.

But essentially this puzzle relies on the ambient noise level in a room dropping below a certain threshold for 15 second. In practice this would mean that there would be a record player or a radio in the escape room that ensures a high level of background noise so that the puzzle can only be activated once that noise source has been turned off.

The electronics inside are rather straightforward, but also a total nightmare. I decided to use an off the shelf audio level meter kit, a condenser microphone and preamplifier and an arduino nano.
In practice the preamp drives the level meter, while the arduino uses an analog pin to also monitor the audio output pin from the amplifier. The arduino nano is driving 6 large bicolour LEDs from 12 of its pins, if the audio crosses a certain threshold all of the LEDs light up read, however once the audio falls below a threshold, the LEDs gradually start turning green, if all of the LEDs turn green a relay is activated and the puzzle hangs for 30 seconds before resetting.

The plinth was just a CAD design, and the ear was a 3D model from thingiverse that I sliced down and scaled to fit. Everything was 3D printed and given a nice coat of white paint. The diffused LED bars at the front were made from hot glue injected into the grooves while the plinth was pressing against a smooth piece of glass, the finish came up amazingly well. Having the microphone in the ear hole seemed the obvious choice.