YouTube Demo link: (115) Rotary Phone Turned into a Kitchen Timer - YouTube
I love the idea of re-purposing and combining old things with modern tech and after seeing a reddit post that inspired me to use a rotary dial, I came up with the idea of using a vintage rotary phone for a kitchen timer.
The project started by searching for a vintage rotary phone at thrift stores. I originally had in mind a classic 50-70s style or french style phone, but then came across this very old wooden box phone
that was originally a hand crank phone. At some point, someone converted it to a rotary phone, and now it gets to serve another life as a kitchen timer. Much more room inside to hide electronics
than a newer rotary phone.
Originally, I was expecting to have to figure out how the 425B network box worked that ran the rotary phone, but then realized I could use the Arduino as the sole controller. I used an
oscilloscope to figure out the pulses off the rotary dial, each pulse was ~60ms high with a 100ms period. Each number is 1 pulse and a 0 is 10 pulses. The next main challenge was how
to operate the original ringer (I really didn't want to resort to using a speaker). In North America, phone ringers run off 60-90VAC and 20Hz. I found a small company called
'Cambridge Electronics Laboratories' that sells 'Black Magic' ring generators of various input and output voltages. I purchased a 5VDC input sine wave generator so I could use the
same power supply as the Arduino. This ring generator creates a lot of electrical noise and I had to add a filter capacitor to the handset input otherwise it would frequently false trigger.
One of the main goals of the project was to keep the vintage look. So I opted for a red 7-segment display with a black 3D-printed housing. The labels are hand stamped brass with small red status lights next to them. The switch on the back is a large metal switch with a heavy analog feel.
Hopefully this project inspires others to re-purpose items and create fun arduino projects!
Here's the GitHub Repo: Scott-28/Rotary_Phone_Timer: Rotary_Phone_Timer is an Arduino Uno based project that turns a vintage rotary dial phone into a kitchen (or general purpose) timer. (github.com)
