How to Design a Smart Home Door Lock
By: Sean Scannell, Associate Product Manager
Introduction
Access control technology for homes, vacation rentals, and apartments is experiencing growing demand to facilitate services like short-term rentals, dog walking, and package delivery. This growth brings increased concerns about safety and ensuring only authorized access is granted, complicated by varying requirements across different smart applications. This whitepaper demonstrates how to address these challenges using a Zigbee Door Lock reference platform. This platform is modular, allowing for dual or multi-authentication schemes using various inputs and sensors. It covers popular methods including facial recognition, fingerprint ID, mobile applications, and manual keypad entry, all powered by the Zigbee Door Lock Reference Kit based on the Silicon Labs EFR32MG21 Development Kit (supporting Zigbee, Thread, and Bluetooth).
What Does a Smart Home Door Lock Offer?
A smart door lock transforms a frequently used entry point into a connected device, removing the need for physical keys and offering remote access control. Users gain peace of mind, knowing they can grant access without being physically present, letting guests inside via a smartphone. Smart door locks can also sync with other smart home products for added utility, making them ideal for short-term rentals, cleaning, and maintenance services. Users can lock or unlock their doors remotely from their smartphone, eliminating worries about forgetting to secure their home. Silicon Labs aims to help customers realize the smart home's full potential by providing innovative, easy-to-use products and detailed documentation.
Scaling Your Smart Home Through an Ecosystem
A smart door lock can be integrated into an ecosystem of other smart devices, enabling unified control over lights, entertainment, and climate systems. Leveraging an ecosystem Internet of Things (IoT) partner can simplify development by combining a smart door lock with additional smart home devices. The 2020 ABI Smart Home Market Report projects the IoT industry to reach $3.3 billion by 2025, with approximately 80 percent of products expected to exist within at least one ecosystem. Ecosystems offer pre-established integration for networking, routing, and cloud services, along with pre-built smartphone profiles. This allows designers to focus on their core expertise, differentiating their products rather than spending time on non-core functionalities. Ecosystems also provide a standardized infrastructure, ensuring long-term compatibility and increasing product lifespan.
A diagram illustrates how to scale smart home solutions through an ecosystem. It shows a central 'Leverage Ecosystem' concept connecting to 'Cloud Service', 'Smartphone App', 'Partner Device', and 'Network Infrastructure (Gateway/Router/Smart Speaker)'. Supporting text highlights benefits like focusing on core competency, scaling resources, fast time to market, and expanding market exposure.
Smart Home Market Growth and Ecosystem Adoption
| Year | Total Smart Home Market (USD Millions) | In Ecosystem (%) |
|---|---|---|
| 2019 | 1,289 | 40 |
| 2022 | 2,681 | 60 |
| 2025 | 3,362 | 80 |
| *CAGR: 17.3% (for the period)* | ||
How to Select Your Smart Home Technology
To join an ecosystem, your smart home device must communicate using the ecosystem's wireless technology. Established ecosystems utilize protocols such as Wi-Fi, Bluetooth, ZigBee, Thread, and Z-Wave. Each protocol offers distinct strengths, including reliable connectivity independent of Wi-Fi services, ensuring continued operation even if Wi-Fi is unavailable.
For its smart door lock solutions, Silicon Labs selected the Zigbee protocol, based on the IEEE 802.15.4 specification. Zigbee operates in the 2.4 GHz bandwidth range and has been a prominent IoT protocol since 2002, used in ecosystems like Amazon and Samsung SmartThings. With over half a billion Zigbee chips deployed globally, it has a proven track record in the smart home market. Zigbee supports large networks, up to 65,000 nodes, and offers pre-designed low-power support for coin-cell battery operation, reducing form factor constraints, fully supported by its green power feature. The network is designed for security, utilizing self-forming and self-healing capabilities to maintain network integrity. Zigbee also comes with pre-certified stacks and reference designs.
A visual representation highlights Zigbee's advantages: 'Reliable and Independent of Internet Connectivity', 'Robust Large Networks', and 'Battery Optimized'.
Another diagram shows the ecosystem structure, with a central 'ECOSYSTEM' box connecting to 'Cloud Service', 'Smartphone App', 'Partner Device', and 'Network Infrastructure', alongside 'LOCAL DEVICE TO DEVICE' communication.
Interactive Options
Beyond selecting the wireless technology, several system requirements for a smart home door lock must be considered: how the phone connects to the ecosystem, how the deadbolt is controlled, and the authentication modes to be used. Phone connectivity is crucial, requiring a smartphone with over-the-air (OTA) update capabilities. Bluetooth is a suitable choice for local control and OTA updates. Deadbolt control involves motor control to extend or retract the deadbolt. Authentication modes offer various options; this project utilizes three:
- Keypad Codes: A common and robust option, not dependent on connectivity. Keypads enable features like single-use codes and time-expiring codes, popular for short-term rentals.
- Fingerprint Recognition: Requires minimal user interaction, offering fast access by simply pressing a finger to the sensor.
- Facial Recognition: A high-end feature that is more complex and costly to implement. It is highly interactive and has gained popularity through smartphone adoption.
Silicon Labs Platform Solves Key Smart Home Door Lock Needs
The choice of microcontroller (MCU) is critical, as it dictates the door lock's smart functionality. Silicon Labs selected the EFR32 Wireless Gecko, an IoT-focused wireless SoC known for its robust RF performance across 2.4 GHz and sub-GHz frequencies, optimum output power, and high sensitivity. It also provides optimized power performance with low active and sleep currents for extended battery life. Key features for door locks include excellent ecosystem interoperability and built-in security, such as end-to-end encryption and tamper protection. Silicon Labs also offers pre-certified modules, reducing developer effort.
The main system controller kit features the EFR32MG21 Development Kit, which manages authentication, network, and mobile integrations. For deadbolt control, an Uxcell a1409 Open Frame Actuator is used, communicating via standard general-purpose input/output (GPIO). Code authentication is enabled by the Micro Robotics TTP229 4x4 Keypad Kit. Fingerprint recognition is handled by the Sunrom R307 sensor, and facial recognition by the Omron B5T face recognition kit.
A block diagram of the smart door lock system shows the central EFR32MG21 microcontroller. It connects via GPIO, UART, and I2C to a solenoid for deadbolt control, a keypad, a fingerprint sensor (R307), and a face recognition module (Omron B5T). The diagram also indicates Bluetooth and Zigbee controllers.
Building the Smart Door Lock
The reference design and code for this smart door lock are available on GitHub. The design provides a user interface for authentication modes, allowing switching between options and supporting 1-step and 2-step authentications for enhanced security. General features include OTA provisioning and updates, basic driver architectures for EFR32, and power management for active and sleep states.
A mobile app, based on Silicon Labs' EFR Connect app, is also provided, facilitating Bluetooth connection between a smartphone and the board. The Zigbee implementation involves powering on both devices, forming the Zigbee network by pressing PB1 on one device, and joining the network by pressing PB1 on the other. After the Pan ID is displayed, pressing PB1 on the switch device discovers and binds to the lock device, and pressing PB1 on the lock device closes the network. Subsequently, PB0 on the switch device toggles the door lock, with status feedback returned.
A step-by-step flow chart details the Zigbee network implementation: powering devices, forming the network, joining the network, discovering and binding devices, closing the network, and controlling the door lock via a button press, with status feedback.
Smart Door Lock App
The EFR Connect app is a developer-focused application built for simplicity, highlighting key Bluetooth Low Energy (BLE) metrics. It includes developer features such as simultaneous connections for broader visibility, logging and exporting BLE activity, and powerful filtering options to identify devices. The source code is accessible on GitHub.
A list of features for the EFR Connect app emphasizes 'App-delivered tools support BLE code development', 'Simultaneous connections for broader visibility', 'Log and export BLE activity', 'Powerful filtering options to identify devices', and availability on iOS/Android with source code on GitHub.
The app template provides device discovery, door lock control, event history, and passcode security. To establish a Bluetooth connection, users open the Silicon Labs application, initiate scanning, and connect to the desired device. Filtering by RSSI (e.g., -48 dBm) can narrow the search. The DMP4428 is the recommended door lock device. Upon connection, a status update is received. Users can then enter their password in the app to change the door lock status. Video demonstrations of the application are available on the Works With session page.
Conclusion
When developing any IoT application, non-technical considerations are important. These include assessing the market opportunity, which for smart door locks appears healthy with room for innovation. Determining the target segment—whether low-cost, easy-entry locks or high-end models with advanced features—is also key. Developers must also determine product cost, profit requirements, and sales channels. Thoroughly addressing these steps can significantly impact time-to-market and the quality of the final product.
For more information about Silicon Labs' offerings in this area, visit https://www.silabs.com/solutions/smart-home/locks.
Information regarding the 'Works With' event, held September 14-15, 2021, is also available for those seeking more tools and training for innovative Smart Home IoT products.
