Low-Power Wireless Temperature Sensor for Health Monitoring

Abstract

Patients with severe health problems often require permanent monitoring using low-power devices for a modern superior medical care. In this paper the design concept and implementation of a low-power medical wireless temperature sensor using hardware reconfigurable devices as an alternative to standard microcontrollers will be described. A hardware design with a Xilinx Coolrunner2 CPLD and high accuracy medical temperature sensor as main parts is presented.

Existing System

Wireless Sensor Network Solutions for Healthcare Monitoring.

Proposed System

Although CPLDs are mainly used in applications where speed is a critical parameter, in this paper proposes system, CPLD was preferred as a controller for its low-power consumption, flexibility in implementation of control functions and most common communication protocol (e.g. I2C, SPI, UART, CAN, etc.). The design diagram is built to operate as a wireless sensor node; the transceiver must be initialized with the network parameters such as network id and node address. Therefore, at power-up CPLD must initialize the system with the configuration parameters. The initialization of these two components can be performed in the same time, which is a specific characteristic of CPLD. These parameters, along with other information needed for system configuration and initialization, are stored in the 1 kb EEPROM. After the initialization stage, the controller performs a temperature read operation via I2C communication bus form the sensor and then it sends the data to the transceiver for a wireless transmission to the base station. When this first read temperature is done, the controller goes into the timer mode and performs a new read every two minutes. After every read the controller compares the read data with default temperature or user defined thresholds and if two consecutive read values are above or below the thresholds the controller sends the data to the base station in order to alarm the medical personnel. The default upper threshold is set which is slightly above the normal temperature of the human body while the lower threshold for hypothermia monitoring. These thresholds can be configured by the user and stored in the configuration memory, through the configuration interface or wireless from the base station. The controller also reads a new temperature every 10 minutes and sends the data to the base station whatever or not the read data is above threshold. This feature makes the system fail-safe, emitting an alarm if the base station does not receive a message from the node for a period of time longer than 10 minutes. After a read operation from the sensor or a transmission to the base station is made, the temperature sensor and transceiver are put into the shutdown mode in order to save power.

Architecture

BLOCK DIAGRAM