In my previous post, I tore apart a Flume water monitor and traced its communication path from the sensor, through the bridge, and up to Flume’s cloud MQTT server. I identified the encryption library (LibHydrogen), extracted a firmware ELF, and even managed to coerce the bridge into sending plaintext by corrupting the public key in flash. But that approach was destructive; the bridge couldn’t complete its handshake with Flume’s server, so real data stopped flowing.

Thinking I had reached a dead end, only to find another path turned out to be a pretty common occurrence for me. More and more thoughts on what I could have done differently, and what further research I could have done kept coming to me. And so I set out to continue to pursue my unhealthy obsession of figuring out exactly how I can read this data on the network.

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About a year ago, I bought a smart home water monitor in order to keep an eye my water use at home. The city where I live provides a big rebate on one particular device from San Luis Obispo company Flume. I was immediately curious about how this device could work and was excited to open the box when it arrived and inspect the contents.

There are two hardware components in this system. One component, the sensor, is designed to be physically strapped to your water meter. The other component, the bridge, receives information from the sensor and connects to the Internet via Wi-Fi to deliver all this data to Flume. Flume provides an API for customers to access their own data and there’s even a Home Assistant plugin which should help bring all this information to the platform I run at home.

But I wanted to learn more about how this all works and was curious if there could be a way to access this data more directly. As friendly as Flume seems to be, I do feel that if I buy a device to track my own data, that data should belong to me. But also, it would be nice to know that if Flume ever closes up shop or shuts down its web service, that these devices could all still be useful. So let’s take a closer look at the hardware to see what’s really happening.

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In 2023, I managed to integrate my garage doors with HomeAssistant using a Shelly Uni device. Controlled remote operation is pretty great, but I wanted to document this project because this solution covers remote door control, door state and even door light control is possible, using a single $12 device with no batteries required. The setup is easy to achieve, and leaves all the garage door opener functionality in tact.

Overview

• Shelly Uni device is powered from a 12v DC power source leeched from the low-voltage side of the garage door control circuit board
• Garage door switch is operated using one of the two potential free outputs on the Shelly Uni
• Garage door state is monitored using both Shelly Uni inputs, detecting open/closed circuits on the garage door opener’s own state sensors
• Light control is not implemented, but could be added to the extra Shelly Uni output in an extremely simple circuit

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A binary clock is hardly a new idea, but this particular concept is something I haven’t seen anywhere else. And it was idling in the back of my mind for over a decade before finally seeing a working prototype.

Concept

The passage of time can be measured in any number of ways, but when a clock is designed for humans, I think it should be based on a natural concept. Since I live on Earth, I designed a clock, as many others have, based on the smallest natural temporal concept I can readily observe: the day.

The day is plenty useful for medium-term planning, but it lacks the precision needed for many purposes, and so it must be divided in order to build a useful clock. This is where clock design becomes much more arbitrary. Dividing the day into 24 was supposedly based on astronomical observations of various stars passing in the night, but beyond that, there’s no natural reason there should be 60 minutes in an hour and so on.

My thought, is that the simplest and most natural way to divide a day would be in half. This is essentially the AM/PM indicator which is a concept so natural and necessary, that even many of our 12 hour clocks use it to avoid the otherwise ambiguous information displayed. But if the most natural way to divide a day is in two, then maybe the next most natural division is in two again. Dividing a day repeatedly in two results in a kind of binary clock. And this is exactly the concept.

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Now that TLS is free, there’s very little excuse to be running web services over plain HTTP. The easiest way to add TLS to this blog was through AWS Certificate Manager and its native CloudFront Support. But for a while, there was a problem. In order to use a free, trusted certificate from Amazon, I needed to be using CloudFront. In order to be using CloudFront, I needed to be able to resolve the name ‘lithostech.com’ to a CloudFront distribution. Since DNS doesn’t support CNAME records on top level names, that meant switching DNS service to Route53 where Amazon has a special solution for this problem they call alias records.

But there was a problem because Route53 doesn’t have DDNS support and I use DDNS to reach my home network’s dynamic IP address when I’m out of the house. And so I put this off for quite a while, mostly because I didn’t realize how simple DDNS really was and how easily it could be done with AWS Lambda.

Turning to the source code for ddclient, a popular DDNS client that ships with Debian, I found that DDNS amounts to nothing more than calling a tiny web API to update a remote server with your current IP address at regular intervals. Each vendor that provides DDNS seems to implement it differently, and so it seems there is no specific way to do this. But in all the implementations I saw, the design was essentially a magic URL that anyone in the world can access and use it to update the IP address of a DNS A record.

A picture was beginning to form on how this could be done with very low cost on AWS:

• API Gateway (web accessible endpoint)
• Route53 (DNS host)
• Lambda (process the web request and update DNS)
• IAM Role (policy to allow the DNS changes)

On the client side, the only requirement is to be able to be able to access the web with an HTTP(S) client. In my case, a CURL command in an hourly cron job fit the bill. I enjoy the flexibility of being able to implement and consume this as a tiny web service, but it could be made simpler and more secure by having the client consume the AWS API to invoke the lambda function directly rather than through the API Gateway.

I put some effort into making sure this Lambda function was as simple as possible. Outside of aws-sdk, which is available by default in the lambda node 4.3 execution environment, no other npm modules are required. Source code and instructions are available on GitHub.

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