Embedded Systems

The TEMPO System

TEMPO (Technology-Enabled Medical Precision Observation) 3.1 is a third-generation body area sensor system that accurately and precisely captures, processes, and forwards human movement. The system supports up to seven wearable sensors nodes that can be placed at arbitrary points of interest on the human body. Sensors capture both linear and angular acceleration in three axes or six degrees-of-freedom. Each sensor node is a custom design and system integration of commercial off-the-shelf (COTs) integrated circuits (ICs) on printed circuit board (PCB). TEMPO circuit boards are encased in one of several custom high-impact polystyrene enclosures manufactured by a stereolithography process. Enclosures are molded to ergonomically fit specific body placements including the wrists, ankles, forehead, and chest/sacrum.

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On-node linear inertial sensing is enabled by the Freescale MMA7261 three axis, monolithic, micromachined accelerometer. The sensor features selectable sensitivity between ±2.5 g and ±10 g to accommodate a variety of applications. Two micromachined gyroscopes, the InvenSense IDG-300 and Analog Devices ADXRS610, provide all three axes of angular rate to at least ±300 degrees per second. These two sensing elements give TEMPO3.1 the ability to capture human movement with six-degrees-of-freedom.

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Sensor outputs are conditioned by single-pole low-pass filters with 60 Hz cutoff frequencies. The six conditioned signals, in addition to 2 calibration references, are captured by the 8 12-bit analog to digital converter (ADC) channels on the Texas Instruments MSP430F1611 mixed-signal processor. Conditioned signals are typically sampled by the ADC at 120 Hz – a bandwidth exceeding the characteristic response of human movement. At this sampling frequency/resolution, and without compression, each sensor node produces data at a rate of ~10 kbps. The MSP430 processor operates at 4 MHz by a digitally-controlled oscillator synchronized to a low-power 32 kHz crystal. The sensor node also encapsulates power management circuitry that provides regulated 3.3 V and 5.0 V outputs. Each regulator is fed by a 3.7 V, 300 mAh rechargeable lithium-ion coin cell battery. At full power, the sensor node can run for ~4-6 hours.

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The mixed-signal processor facilitates digital signal processing (DSP) capabilities as well as control over other integrated peripherals and system ICs. A proprietary operating system, TEMPOS, schedules procedures, handles user input/output (I/O), and cycles between various low-power modes during periods of inactivity. The operating system also enables device reprogrammability, a feature that allows TEMPO 3.1 to satisfy the requirements of emergent applications.

Sensor nodes externally communicate via Roving Networks RN-41 Class 1, Bluetooth 2.0 transceiver module. The module interfaces the mixed-signal processor via 115.2 kBaud UART serial bus. Nodes are assembled into a star topology network controlled by a central data aggregator (PC or handheld computer). The TEMPO aggregator software forms a Bluetooth piconet that supports up to seven sensor nodes. Nodes are sequentially interrogated by the aggregator in a round-robin schedule. The aggregator also provides a master clock to which nodes synchronize time.

TEMPO System Streaming to a Laptop with Custom Signal Processing Software
The CHEST System

The CHEST system (Configurable Heterogeneous Embedded Sensor Technology) is a wearable physiological monitor that integrates heterogeneous sensors and can be configured for different applications. It was initially motivated by psychology research, in which human emotions are studied by measuring physiological parameters. The system was designed to be capable of monitoring the body temperature, heart rate, and motion (via accelerations), and data is stored for later analysis. This system can be configured in a variety of ways to be optimized for specific applications, including medical diagnosis.

The CHEST System

Major challenges in designing this system are divided into three areas: wearability, heterogeneity, and configurability. The wearable monitor needs to be small in size and weight, so it allows people to carry out daily activities while wearing the system, and it needs to be low-power, so it allows for continuous operation for an extended period using a small rechargeable battery. Off-the-shelf surface-mount components were selected to make the system small enough to be wearable, and specific sensors and components were selected to minimize power consumption. Sensor circuits were designed to interface heterogeneous sensors with different electrical characteristics to the microcontroller for data acquisition. In addition, a low-power microcontroller was used to integrate heterogeneous sensors and provide different configurations. Acquired data was stored in a flash memory to be analyzed on a PC. Different configurations were implemented in the firmware with sampling rates and signal processing techniques that can be adjusted based on application requirements.
The RESPOND System

The RESPOND system (Remote Embedded Solution for Physiological Observation of Networked Devices) is designed to relay important medical and position data of emergency response personnel to a monitoring station. The system works with Empirical Technology Corporation’s systems, such as the BP Guardian, that measure physiological data like heart rate, blood pressure, etc. The RESPOND system communicates with one of these physiological measurement systems using a low-power radio protocol such as bluetooth or Dynastream’s ANT Protocol. In addition, there is a GPS reciever on-board to obtain the user’s position in case an emergency arises where he or she needs additional help. This data is then sent to the monitoring station in one of two ways. First, the data can be sent over a GSM cell network so it can be transmitted virtually anywhere. One problem with using a cell network is that medical personnel may be in situations where there is little cell coverage. For instance, a first responder may in the wilderness or in a large shielded building. In this case, the data can be sent over a low frequency (151 MHz), long range two-way radio communication channel to a base station up to a few miles away allowing for both physiology and position monitoring where cell networks fail. The RESPOND system uses the TI MSP430 microprocessor to communicate between wireless radios, which allows for easy interfacing while preserving most of the battery power for the radios.

The RESPOND System

The RESPOND system allows for remote monitoring of emergency response personnel, and can be modified and used as a communicaton hub for almost any wireless capable data-logging device. Though the current revision is only a prototype, this system could prove very useful as a medical communication hub used to relay data taken in other INERTIA team projects.