Application Focus: Wi-Fi Sensors
Sensing application are numerous across a wide spectrum of commercial and consumer for example monitoring temperature, humidity, air quality, moisture content, lighting levels. There is an accelerating trend to deploy wireless sensors. Wireless sensors have a distinct advantage over wired sensors in that they have low installation cost and rapid scalability.
The possible applications for wireless sensors are nearly endless. Consider monitoring food temperature across a line of distributors and grocery stores. Freezers and coolers can be conveniently and reliably monitored, alerting staff to fluctuations before costly spoilage occurs. Another common application in residential homes is monitoring water levels in basements or carbon monoxide. These systems can be programmed to email or text warnings. Another advantage of wireless sensor networks include eliminating expensive retrofit wiring in existing buildings. Today wireless sensor networks are monitoring campuses, office buildings, manufacturing plants and residential homes.
Wi-Fi Modules and Sensor Networks
Low-power, low cost Wi-Fi modules have changed the landscape of wireless sensor networks. Autonomous, Wi-Fi sensors connect to common, widely available wireless network infrastructure. They send sensor data over standard TCP/IP making their information anywhere in the world from any computer or smart phone.
Previously, wireless sensors networks have been built on top of proprietary protocols running on sub-gigahertz radios. These systems have the benefit of covering long distances however they are closed systems. Likewise sensors networks based Zigbee radios are also closed system. Both of these wireless sensor networks require additional gateway hardware devices to get sensor data onto the internet or users LAN. Gateways introduce a single point of failure and additional cost.
Built on standard 802.11 b/g Wi-Fi infrastructure, remote sensor networks contains three main components: battery-powered sensor, standard Wi-Fi access points, and server software that receives, stores and presents sensor data. Sensor information can be viewed from device on the network or if desired from any Internet-accessible location. If the sensor is not in range of the Wi-Fi access point additional access points can be added as repeaters. The sensor only needs to know the SSID and pass phrase to join the network; and with the pre-programmed IP or URL address, the sensor can start sending data to the server.
The sensor can intelligently send data to the server based on a time period, sensor event or even if the data meets a programmed criteria. All of this can be controlled from the server through provision of the sensor when it first connects. If the network goes down or sensor goes out of range, data is cached on the sensor. When the network comes back the sensor can catch up with the server.
Roving Networks Wi-Fi Solutions for
Roving Networks Wi-Fi Sensor Reference design allows customers to quickly build a remote sensor system, slashing development effort and time to market. The Coolbox sensor is a single external 100 Ohm RTD temperature. Reporting to the server every two minutes, the Coolbox sensor runs for more than a year off two AA batteries.
Most impressive is that the Coolbox is built with little more than the battery, temperature probe and Roving Networks RN-131 Wi-Fi module. The RN-131 module contains the complete TCP/IP stack, sensor client application and analog sensors for directly connecting the sensor. This makes for a very low cost Wireless sensor node.