2020-12-23 | By Maker.io Staff

Wireless Wifi ESP32 ESP8266

In an attempt to keep our houses safe, the consumer electronics industry has been developing several platforms for home security, monitoring, and remote control. Recent advances in the Internet Of Things (IoT), micro-electromechanical systems (MEMS) sensing devices, and low-cost microcontrollers and cameras have all contributed towards affordable and extensible home security and monitoring devices. The layer of IoT over the devices enables their remote monitoring and control over the internet, thus making them more useful and accessible.

Several sensor modules, networking modules, and microcontrollers are available for hobbyists and makers to build their own home monitoring and IoT ecosystem. This blog explains the various sensors, sensor network topology, control platforms, and several maker tools for creating such systems at home.

Indoor Monitoring Sensors & Mechanisms

Monitoring devices rarely have any controlled elements and are just meant to detect unexpected activities in the house - like a gas leak, fire, the plants going dry, or extremely high-speed winds. The most common physical quantities measured in a house include sound, temperature, humidity, air quality, hazardous gas, and plant health (soil temperature and soil moisture), among others.

The common security monitoring devices include motion detectors and burglar alarms, while face recognition-based and numeric keypad-based house doors and lockers are common safety systems. IoT allows configuring (changing passwords and permanent locking) these safety platforms remotely, thus making them more reliable and adaptable.

In an automation system, these sensors can also trigger the appropriate response, like watering the plants when they have low moisture or calling the fire brigade in case of a fire. While individual commercial devices do exist for each of these sensing mechanisms, the sensors and controller boards are low cost and readily accessible for makers and hobbyists to build their own platforms.

(Image source: original image created by author using screenshots from DigiKey pages)

Sensor Node

A sensor node is a standalone device measuring physical quantity somewhere in the system. Multiple sensor nodes are connected to create a more holistic and sustainable sensor network. It is the smallest unit of security/monitoring IoT system, connected to each other or a central node, ideally, wirelessly.

Each sensor node comprises a physical sensor/transducer element, a microcontroller, a wireless communication mechanism -- usually Wi-Fi -- and a power source like a battery or a wall charger. Each sensor node is ideally low-cost and low-power. The microcontroller is usually programmed to sense and transfer data to the aggregator as well as to append the incoming data from other sensors (depending on the topology) before passing it forward.

Sensor Node (Image Source - Original)

Sensor nodes also send metadata which includes information about the time of the day, the node identity, location, and status elements like battery power, sensor connectivity, and processing status. These values help localize information and invoke control action as per the location and need.

Wireless Sensor Network

A wireless sensor network refers to a group of sensor nodes working independently, monitoring different physical quantities, and also logging their values at a particular aggregation location, locally or over the internet. Traditionally such networks have been unidirectional and only supported data transfer from sensor nodes to the central repository; but recent automation elements have introduced bidirectional communication where control action can also be initiated from the central node to a particular sensor or actuator node.

Sensor networks or meshes have different topologies for data transfer routes. For example, all nodes may be directly connected to the central node, and the failure of the central node can lead to a complete system collapse.

The various sensor network topologies used under different considerations are:

1. Point-to-Point - A topology with one sensor node and other central/aggregator nodes.
2. Linear - Each node is connected to a successor and a predecessor node and has two terminal endpoints.
3. Bus - All nodes connect to a central message bus.
4. Ring - Each node is connected to two others and the terminal nodes are also connected to form a cycle.
5. Star - Each node is connected to one central node called the hub.
6. Tree - It manages a hierarchy of nodes where each parent node is connected to multiple other children nodes.

Different sensor node topologies (Image Source - Original)

A sensor mesh is a network where data can be transferred along multiple routes because each node has multiple indirect connections to the other parts of the system. A fully connected mesh is where each node is connected to all other nodes, such that data can be routed from any node to another. This is a robust network, immune to path failures.

Mesh network variants (Image Source - Original)

Microcontroller Boards for Sensor Node

Commercially, sensor nodes are developed with low-cost yet robust commercial microcontrollers from Texas Instruments or STM, with several affordable microcontroller boards to build the sensor nodes. A few microcontrollers have native support for wireless communication (onboard Wi-Fi module) while those without are extended using wireless communication boards.

The most common Arduino boards like Uno, Mega, and Nano do not have onboard internet or wireless communication. Arduino Wi-Fi shields and ethernet shields have been used traditionally for communication support. Other wireless transceiver modules like the NRF24L01 have also been used before. Arduino has also recently added a series of development boards with onboard wireless communication support for dedicated IoT development like the Arduino MKR 1000.

ESP32 and ESP8266 are small Wi-Fi microcontroller chips with a complete TCP/IP stack. Several development boards like the NodeMCU (with ESP8266 onboard) and ESP32-DEVKIT (with ESP32 onboard) are commercially available that provide a user-friendly interface and easy interface with many sensors and actuators.

ESP Platforms (Image Source - Screenshots from DigiKey products)

Cloud Infrastructure & Networking Tools

An IoT layer on top of the sensor node ecosystem needs several networking elements to implement the remote monitoring and control element. The significant elements of the IoT layer include:

• Database - A database is a platform for structured/unstructured storage of data for offline processing or retrieval, either stored locally or over the cloud. SQL and MongoDB are common database platforms that can store multi-sensor data over time, which can be retrieved in a computationally efficient effort.
• User Interface - Usually a mobile app or a browser-based interface where users can monitor the various values, their analysis, receive notifications for alarms or events, and more. This interface can be cloud-based for access over the internet or can also have an instance running on the local ecosystem network that doesn’t need an internet connection.
• Data Handling - Data encryption and secure exchange using authentication credentials are needed to implement a safe and secure ecosystem.
• Cloud Platform - Cloud platforms like the AWS IoT, IBM Watson IoT, and Azure IoT are different cloud-based platforms that provide makers and companies a way to handle their data analytics and processing computations securely and reliably.

Conclusion

Affordable development platforms and sensors along with free IoT cloud platforms have opened a plethora of opportunities for the makers and hobbyists to create home sensor monitoring and control ecosystems, avoiding the expensive commercial hardware or the subscription models from the big commercial players.

The ESP boards with their support for almost all sensors and communication protocols are especially accessible and easy-to-use platforms to develop such an ecosystem.