Nightscout is a suite of open source projects. A smartphone provides ubiquitous network connectivity to Dexcom’s wireless receiver. After a polling period the last reading from the Dexcom receiver is transmitted to a database on the Internet. A website renders near-real-time views of the records stored in that database. Additionally, the website offers a RESTful API that a pebble watch can use to display the last known alarm status, trend, and glucose level as reported by the Dexcom receiver.
The Nightscout project is actually a suite of several independent projects:
When assembled, the completed device is called a “Nightscout rig.” In addition to the raw source code for these applications, other community maintained resources exist to help people learn how to assemble their own rigs. These include groups, photos, shared documents, videos on a variety of social media, including a centralized community curated website for documentation as well as community maintained forum software.
This is a web application which simulates the display of a Dexcom receiver. In addition to showing the last known glucose level, it displays when the reading was taken, and offers a way to pan several hours retrospectively.
Every 5 minutes, a node.js server polls a mongo database, emitting the last readings over the last two days to any listeners subscribed to the server’s sgv websocket event. The server also serves a combination of html, css, and javascript to simulate a near-real-time display of the Dexcom receiver.
The web display works on most modern web browsers.
android-uploader is an Android application implemented in java. The application starts when a Dexcom receiver is detected using the operating system’s usb management system. The application reads data from the serial port made available by Dexcom’s usb connection, and uploads the latest record to a specified data backend. The backend may either be a RESTful API or a mongo database, and is configured using a preferences panel in the application.
The android-uploader source code must be compiled and distributed as an APK before it can run on an Android smartphone. Once installed and configured to upload data to the preferred cloud “backend”, a USB OTG cable is used to connect the smartphone to the Dexcom receiver’s micro usb port. The Dexcom receiver is a device cleared by the FDA for continuously monitoring glucose levels sampled from interstitial fluid. The receiver is designed to store and display values transmitted by the Dexcom sensor. android-uploader uses the serial connection provided by this usb capability to exchange data with the Dexcom receiver. The behavior of the uploader has been designed to behave as Dexcom would expect any data management system to behave. There is no expected difference in Dexcom’s behavior when the uploader smartphone is attached or while our software is auditing the records on the Dexcom receiver.
cgm-pebble is a C and javascript watch face developed using PebbleSDK. The javascript code runs on a Smartphone maintaining bluetooth connectivity to the Pebble watch. The javascript code retrieves information from cgm-remote-monitor and sends the last reading to over bluetooth to the pebble watch. The C code runs on the watch, receiving messages over bluetooth from a smartphone, and rendering the date, time, value, and trend as reported by a running instance of cgm-remote-monitor.
Development takes place using Github, from the Nightscout organization page: https://github.com/nightscout/. Modifications, upgrades, development, and issue tracking happen using the resources connected to assets shared by a community of people. Each and every change to the source code is tracked by git and discussed through a Github pull request. Upgrades are provided by providing git merge requests, often using the Github UI, by identifying the last commit hash in use, and a verified change controlled path to apply latest updates from trusted contributors.
The git repositories merely provide the source code, and a verified way of exchanging source code for these projects. In order to be used, the source code must be configured, compiled, deployed, and installed.
While each repository contains instructions on how to test and work with that repository, the Nightscout development guides, forums, youtube videos, pictures, twitter account, and Facebook group provide “educational” material on how people have combined and configured these disparate parts to assemble something resembling a “medical device.” The web guides also reside in a git repository, where improvements are proposed by the community, reviewed, and adopted in similar manner to the source code itself.
The guides explain how to configure and install each component, with warnings of “things that might go wrong” at each phase. When people experience issues following the guides or during use, they use social media to find people that have similar issues or ask for help. There are also recommendations, optimized for cost and predictability, on which service providers are available, as well as how to work with those service providers.