Building an IoT Notification Device from Scratch

Summary

After setting up dozens of Internet of Things (IoT) smart home devices, I started to wonder: how hard could it be to build one from scratch? I needed a project to learn on, so I decided to create something fun: a device that alerts my neighbors when my kids go swimming, extending the invitation for their kids to come swim too. What follows are the lessons I learned from building such an IoT device from scratch. Demo and Code Here's a short video demoing the device and its features: Watch this video on YouTube The instructions and code for building your own Splashflag can be found at the bottom of this post, otherwise keep reading to learn about my journey in building the device. Why SplashFlag? How many times can you play Marco Polo in a pool with an adult and two kids? I know that my kids far prefer the company of their friends who have a lot more energy. Originally our idea was to put up a special "we're swimming" flag outside in our front yard when our kids were in the pool, alerting the neighbors that they are welcome to come over and swim as well. The flag would be an open invitation, without the overhead of planning, group texts, and phone calls. I quickly realized this idea wouldn't work because: 1) The flag wouldn't be easily visible from every neighbor's house 2) By the time people saw the flag and came over, we might already be wrapping up our swimming session What I needed to solve this social problem was technology (or rather, I needed an excuse for a new technology hobby project), which is how the idea for SplashFlag was born. Key Features and Learnings This wasn't my first time building an embedded device, but it was the first time I tried to follow at least some semblance of best practices: main loops less than a thousand lines long, no hardcoded passwords, etc... If this was going to be a true learning project, I wanted to be more organized: use classes, design hardware and software that could handle errors gracefully, and create a way for users to c...