Designing power-efficient and secure home automation systems
Home automation continues to unveil a new era of innovation by providing sophisticated solutions for home and office environments. Systems using microcontrollers are helping consumers by enabling power-efficient, intelligent, and secure home automation systems with intuitive controls and a variety of connectivity options. The latest advancements in security and home automation systems utilize the latest in sensing, connectivity, and computing technologies. For example, nano-scale IC technology is enabling OEMs to build small, affordable, and energy-efficient solutions.
Home automation helps control appliances in home and office environments. Earlier systems were only intended for adjusting lights, turning on/off electrical devices, and controlling the temperature. Today, as part of the Internet of Things (IoT), state-of-the-art embedded systems facilitate intelligent power control and advanced security. With a combination of sensors and processors, the IoT connects different appliances to a central network to enable them to complete their tasks without any user interventionThanks to the Internet, Wi-Fi, and Bluetooth, systems can easily be operated using a smartphone, tablet, or computer.
Basic building blocks of home automation
A typical home automation system requires the following subsystems:
Central Processing Unit (CPU) - The CPU features high performance, low power processors or microcontrollers (MCUs) needed for embedded computing. High-end MCUs support multiple communication interfaces to connect to different peripherals such as sensors, temperature controllers, home appliances, entertainment systems, safety alarms, and security systems. A real-time-operating-system (RTOS) runs on the central control unit to monitor and make necessary decisions, day in and day out.
Connectivity and Communication - Microcontrollers in the CPU need to be connected to networks to communicate with peripherals. As per consumer needs, the network can be either wired or wireless. Mainstream home automation applications use PLC or Ethernet for wired deployments and ZigBee, RF, or Bluetooth LE for wireless connectivity.
Sensors and User Interface - In home automation systems, the CPU is connected to different peripherals including sensors to measure or detect temperature, humidity, daylight, or motion. The CPU also turns actuators and electrical appliances on and off, as well as connects to user interfaces to collect allow remote control and display system status. Earlier user interfaces were built using tactile, mechanical buttons. Today’s automation systems provide a contactless experience using capacitive touch interfaces.
Data Storage - Home automation systems need local storage to store sensor data, user preferences, and the system RTOS. MCUs for IoT applications have built-in Flash memory, but this is not sufficient to store the potential large amount of data generated every day. Integrating more memory within the MCU increases die size, adds to system cost, and impacts the system performance. Large home networks need a separate place for installation of the storage devices. Using large server-based storage devices increases operation and maintenance costs. The challenge for developers lies in trading off between storage capacity and operating cost.
Power Supply Unit - Home automation uses different power options such as high voltage AC lines for electrical appliances and batteries for handheld or portable user interfaces. State-of-the-art systems can now harvest energy from light, vibration, or RF transmissions. Based on present needs and trends, different power modes (low power, standby, active) are also included in the power supply subsystem to facilitate low energy consumption based on common usage cases.
Figure 1 System Overview of Home Automation (Source: Cypress Semiconductor)
A home automation system is actually a consolidated system of different peripherals. There are several design challenges and constraints that need to be considered to meet users’ needs and support value-added applications.
Central Processing Unit
The choice of MCU is critical. MCUs available on the market are differentiated based on different performance parameters like power consumption, speed, computation power, number of GPIOs, and compatibility with different communication protocols and user interfaces. Going beyond traditional architectures, MCUs have changed a lot over the decade. They are now packed with multiple cores, larger memories, more peripherals, and smarter features. The line separating MCUs and programmable system-on-chip (SoC) architecture continues to blur.
In the framework of a home automation system, the CPU needs several control subunits based on the complexity of the design. Subunits interact with the CPU and accept its decisions. There are several topologies that can be used for these types of interactions.
A star topology is most commonly used where all the subunits are connected to a single central unit. The subunits send data acquired from sensors to the central unit. The central unit analyzes the information and sends specific action requests to the subunits. Based on the commands received, each subunit controls its peripherals. In this topology, the failure of one subunit does not affect the operations of other subunits. However, failure of the central unit can shut down the entire system. Therefore, highly complex systems that are intended to operate 24x7 should adopt a mesh or grid configuration. In these topologies, there is more than one central control unit and each of them is connected to the others. Decentralization of processes increases the reliability and the bandwidth of operations. Each unit in this constellation of control units possesses equal intelligence and capability to operate independently. And, if one of the control units fails, the others can take over to maintain uninterrupted operation.
Figure 2 Star and Mesh Network Topology (Source: Cypress Semiconductor)