Unlock Your Front Door by Literally Dialing a Number

I’m interested in both etymology and technology, so linguistic skeuomorphs, anachronyms, and fossil words really light up the part of my brain that feels satisfaction. You might, for example, copy something to your clipboard, then paste it into an email and CC (Carbon Copy) a colleague when you send that to a client’s inbox, which makes me happy. But I promise I’m using the word literally when I say this project lets you unlock a door by dialing a number.

This is, essentially, an electronic door lock that you can disengage by entering a passcode. But unlike similar systems out there, you enter that passcode using an old school rotary phone dial. This has absolutely no practical purpose beyond what you’d get from a system with a numeric keypad, but it is really fun. And as a bonus, ne’er-do-wells might not know how to actually use the dial mechanism, which could increase security.

The operation is pretty straightforward: an Arduino Uno R3 development board monitors the rotary dial and triggers the electric locking mechanism. The Arduino reads the input from the rotary dial by counting pulses. If you’re curious and want to know more about how that works, I go into some detail about it in my own Rotary Dial Volume Control project.

To make the whole thing more convenient to use, Lee Thayer added an LCD screen that shows the digits entered. It helps the user to see what they’ve dialed, since that is an unfamiliar experience for most people today.

The only difficult part of this project is the installation itself. If you’re keen to replicate this, that process will depend heavily on your door, what you want to expose to the outdoors, and what options are available for supplying power. Thayer cut a hole in his door and that is something you may not be willing to do. But I’m sure you can find a workaround if you’re enthusiastic enough about anachronistic security.