Ultra-Low-Power Wi-Fi Module Targets Industrial And Sensor Network Applications
May 8, 2009
When you think of wireless sensor networks for remote monitoring and control, you probably think of ZigBee, Bluetooth, Crossbow, or some proprietary ISM-based (industrial, scientific, medical) radios. While such networks work fine, there is always the issue of tying them to an enterprise local-area network (LAN) or the Internet, and that takes extra work. Now you can use Wi-Fi for such applications with minimal interfacing issues thanks to the Redpine Signals SenSiFi 802.11n wireless module (Fig. 1). It has all the features and benefits of a Wi-Fi transceiver but with features making it directly applicable to sensor applications. Also, it has the low power consumption to make it practical. Designated the RS9119-N-11-31, the module is based on Redpine’s RS9110 system-on-a-chip (SoC), a complete Wi-Fi radio on-chip compatible with 802.11b/g/n standards in single-stream mode, not multiple-input multiple-output (MIMO). It also includes a built-in antenna, frequency reference, power management, firmware in flash, and a variety of interfaces (Fig. 2). The module can collect a full range of telemetry information including temperature, humidity, motion, light, pressure, location, and battery level through standard analog and digital sensor interfaces. The microcontroller, an Atmel ATXMEGA64, implements a small, embedded operating system on which multiple applications can be built. The fully selfcontained module includes standardscompliant wireless LAN (WLAN) functionality with WPA2 security, a network stack that terminates TCP/IP and UDP connections with IPv6 capability, and configuration capability through UART or wireless. Interfaces include UART, SPI, I2C, JTAG, and GPIO. A 10-bit analogto- digital converter (ADC) is provided for sensor data conversion. The module is available in a 31- by 44-mm quad flat no-lead (QFN) package. The SenSiFi is built for extremely low power consumption of 2.4 to 3.6 V using system-level and profile-driven finegrained power control, a microcontroller with an ultra-low-power mode working off a low-frequency clock source, and a WLAN subsystem with multiple power modes. With a single 3-V, 2000-mAh battery and uploading sensor data every two minutes over an IPv6 framework, it can achieve more than three years of battery life. Its high-performance WLAN subsystem further enhances range and effectiveness of data transfer while saving energy. The module is available for evaluation through a fully implemented evaluation board that integrates temperature, humidity, and pressure sensors, an accelerometer, battery management, fullfunctional firmware for WLAN protocol and device control, a configuration utility, and a Web-based tracking application that provides a graphical representation of sensor data. Redpine also provides sample sensor management functions on the microcontroller, along with application programming interfaces (APIs) for applications development. The module is sampling now.