There are two things that the Stranger Things TV show is known for: creepiness and sweet, sweet '80s nostalgia. A company associated with the premiere of the new season of Stranger Things approached Guy Dupont and asked him to build a prop for the premiere event. In keeping with the show's theme, Dupont chose to convert an '80s landline phone to play eerie calls when attendees pick up the handset.
Dupont is quick to point out that this phone didn't end up making it to the premiere because of some sort of logistics snafu. But the project is still cool to see in action and utilizes some clever solutions. As usual, Dupont does a great job of explaining his reasoning and those lessons apply to most maker projects. In this case, Dupont was working under tight time and budget constraints. But he still pulled off something quite interesting.
The completed phone looks like any other from the '80s — including the one you probably had hanging on your kitchen wall. Every now and then, it will start ringing. If someone picks up the handset, a recorded "phone call" will play through the receiver. At any other time, picking up the handset and pushing buttons will cause the standard tones to play and then a busy signal will blare through the receiver.
Dupon only kept two electronic parts from the original phone: the keypad and the receiver speaker. The brain of the retrofitted phone is a SparkFun Thing Plus RP2040 board and plays audio through an I2S audio module. The ringer audio clips pump out through a speaker in the phone's base, but all of the other audio clips play through the handset receiver speaker.
To avoid using two audio modules and amplifiers, Dupont came up with an ingenious workaround. Each audio file is mixed to play audio only on either the left or right channel. The left channel of the audio module connects to the ringer speaker, while the right channel connects to the handset speaker. This lets Dupont choose which speaker the audio clip plays through.
It's unfortunate that Dupont's creation didn't end up at the premiere, but we're impressed with his work regardless.