When [the-rene] was building an escape room, he decided to have a clue delivered by radio. Well, not exactly radio, but rather an old-fashioned radio that lets you tune to a faux radio station that asks a riddle. When you solve the riddle, a secret compartment opens up. [the-rene] says you could have the compartment contain a key or a clue or even a cookie.
The outer case is actually an old radio gutted for this purpose. In addition, a laser cut box and a servo motor form the secret compartment.
The inside of the radio is decidedly modern. A Raspberry Pi B+ and a ATmega328 handle the various functions. Custom PCBs contain the computers and a few other items such as an analog to digital converter (for reading a potentiometer) and an audio amplifier.
The software plays noise until the tuning knob moves near one of six different frequencies. Each frequency can have its own riddle. Of course, the audio is all digital playback, so the frequency is just for effect. There’s no real radio reception going on here at all.