A Walk-Through of a Full Nerves Application - Rob Raisch - Elixir Meetup #3

Explore the session on developing IoT apps using Nerves and Elixir. He walked the audience through a full Nerves application, showcasing its capabilities and providing insights into building robust, fault-tolerant, and maintainable embedded systems.

About Rob Raisch

Rob Raisch is the Chief Architect of Monitoring Integration at SimpliSafe, Inc., with over 40 years of experience in the software industry. He has a rich background in Internet technologies, having contributed to the design of HTTP, HTML, and CSS as an early member of the Internet Engineering Task Force (IETF).

Understanding Nerves

Introduction to Nerves

Nerves is a powerful IoT platform for Elixir/Erlang, designed to build and deploy robust embedded systems. It provides a comprehensive suite of tools and libraries to streamline the development process.

Key Features:

• Fault Tolerance: Build systems that can recover from failures.
• Self-Healing: Automatically restore functionality.
• Ease of Maintenance: Simplified deployment and updates.

Developing with Nerves

The Base Station Example

Rob demonstrated a full Nerves application by creating a proof of concept for a home security base station. This system includes a base station, sensors, and a cloud infrastructure that communicates with dispatch partners.

Components:

• Base Station: Central hub that receives signals from sensors.
• Sensors: Entry, motion, and glass break sensors.
• Cloud Integration: Dispatches alerts to first responders.

Setting Up the Environment

Rob explained the steps to set up a Nerves project, including installing dependencies, configuring the project, and flashing firmware onto the target device.

Setup Steps:

• Install Dependencies: Use mix deps.get to install necessary libraries.
• Configure Project: Define configurations in mix.exs and config.exs.
• Flash Firmware: Use mix firmware to build and upload firmware.

Application Structure

Directory Layout

The Nerves application is structured into multiple concurrent applications running on the Erlang runtime system (ERTS). Each application handles different aspects of the system.

Key Directories:

• Firmware: Contains the main application logic.
• Heartbeat: Manages heartbeat signals for status monitoring.
• Hardware: Interfaces with GPIO pins on the Raspberry Pi.
• WebSocket: Manages real-time communication with the UI.

Event State Machine

Rob detailed the implementation of an event state machine using gen_statem to manage the base station's states, such as off, home, away, and alarming. Each state handles specific events and transitions.

States:

• Off: No sensors are monitored.
• Home: Monitors entry and glass break sensors.
• Away: Monitors all sensors with a delay for exit.
• Alarming: Triggers alarms and notifies the cloud.

Live Demo

Demonstrating the System

Rob conducted a live demo of the base station running on a Raspberry Pi 4. He showed how the system responds to different sensor signals and transitions between states.

Demo Highlights:

• Real-Time LED Indicators: Visual feedback for state changes.
• WebSocket UI: Interactive interface to control and monitor the system.
• Hot Swapping Code: Demonstrated updating code without rebooting.

Advanced Features

Hot Swappable Code

Rob showcased the ability to hot swap code on the Nerves device, allowing updates without rebooting. This feature enhances the maintainability and uptime of IoT systems.

Key Points:

• Transient Changes: Temporary updates until reboot.
• Persistent Updates: Techniques for permanent updates.

Best Practices and Challenges

Lessons Learned

Rob shared best practices for developing with Nerves, including managing configurations, optimizing firmware size, and ensuring reliable firmware updates.

Best Practices:

• Use BusyBox: Minimize firmware footprint with BusyBox utilities.
• Data Persistence: Utilize the data partition for persistent storage.
• Secure Access: Implement SSH for secure access and updates.

Conclusion

Rob Raisch’s presentation at Elixir Meetup #3 provided an in-depth look into developing IoT applications with Nerves and Elixir. By leveraging Nerves, developers can build highly reliable and maintainable embedded systems with ease.

Join the Community

Ready to explore the reliability of Elixir and Erlang?

Register for the next Elixir Meetup at Curiosum Meetups: Registration Join our community of Elixir enthusiasts at Elixir LinkedIn Group Prefer watching the presentation? Here’s the video