Compliant Contacts: Hacking Door Locks with Pen Springs

We love hacks around here, and this one is a great example of making some common, everyday things work in uncommon ways. A clever DIY enthusiast, who wishes to remain anonymous, sent us an ingenious project to detect the door lock position in his 1890s-era basement.

The problem was that most home automation devices wouldn't work seamlessly with this vintage house's existing infrastructure. Our expert needed a custom solution to monitor the status of the basement deadbolt. He embarked on a mission to create a sensor using some spare parts, including a BeagleBone Black – a powerful single-board computer.

Enter springs from a ballpoint pen! In a creative twist, our DIY expert used these humble components as compliant contacts for his sensor. The idea was simple: the springs would sit in the door frame and make contact with the deadbolt. Since springs are flexible, their position wasn't too sensitive – compressing them slightly more if they were too close. This allowed for a reliable detection system.

The pair of springs was wired to the BeagleBone Black's GPIO, acting as a switch to sense when there was conductivity between the springs and the deadbolt. However, this wasn't just a plug-it-in-and-it-works project. The sensor was over 15 ft away from the BeagleBone Black, leaving ample opportunity for noise to interfere with the signal.

To combat this issue, our expert created an RC filter to remove high-frequency noise picked up by his sensor. He then added code to handle debounce – ensuring that the sensor wouldn't trigger multiple times due to inherent noise in the springs. It's a testament to the ingenuity of repurposing everyday items for innovative projects like this.

We'd like to extend our gratitude to [Nathan] for sharing his clever hack with us. If you have a DIY project or hack you'd like to share, please get in touch – we love showcasing resourceful solutions and creative reuse of existing components.