In Part III of our consumer application series, let’s take a closer look at consumer applications involving sensors.
MSP430 MCUs as a sensor hub for mobile computing applications
My colleague, Daniel Torres, published an excellent paper on sensor hub in mobile computing applications on Embedded.com. Here are some excerpts:
Sensors in mobile computing are a fundamental part of the human machine interface; sensors help the system identify the context and environmental conditions. Motion sensors such as accelerometers, gyroscopes, and magnetometers identify whether the system is on a flat surface or whether it is being moved or tilted in a certain position. They provide the orientation of the system and also help provide a more accurate position of the system by increasing the resolution of the GPS with dead-reckoning algorithms. They can also be used in conjunction with the Wi-Fi or 3G/4G radios to determine the position of the system inside a building where the GPS signal is not available. They are the preferred interface, and commonly used, in gaming and augmented reality applications. Sensors in mobile computing applications can track ambient light, barometric pressure, touch, temperature, and voice recognition.
The application processor in a typical tablet system is in charge of system management tasks such as power regulation, thermal management, reading sensors, and backlight control. The architecture prevents the main processor from staying in low-power mode for extended period of times because it has to maintain system management tasks, such as reading the sensors, in order to maintain context awareness. Many of these tasks require high sampling rates.
A solution to the problems described above is to use a MSP430-based sensor/aggregation hub controller (see figure below). This system approach helps extend the period of time in which the main processor is in lower power mode and, as a result, reduces the overall system power consumption. This is achieved by aggregating the data coming from the sensors and other modules in order to reduce the interrupt latency on the application processor.
The chart below shows the power savings using a MSP430 MCU-based sensor hub (red line) to read and process sensor data verses using an application processor (orange line) to do the same. This experiment benchmarks the two while running a nine-axis sensor fusion algorithm to determine system orientation (yaw, pitch and roll) using data from accelerometer, gyroscope and magnetometer.
The system current consumption (total board) is significantly lower when the MSP430 sensor hub controller preprocesses and aggregates the incoming data from the motion sensors. The current consumption is reduced as much as 20 percent in some cases. These power savings are more evident when the sensors are sampled more frequently for example – sampling rates ranging from 10mS up to 100mS.
Reducing system cost in sensor hub applications
In typical mobile computing applications, the application processors usually run at a lower voltage of 1.8V while the microcontroller runs at 3.3V. Interfacing a microcontroller to an application processor requires external level translators.
The Texas Instruments MSP430F522x and MSP430F521x devices support a main supply rail (1.8V to 3.6V) and a separate I/O supply rail (1.8V ± 10%), eliminating the need for level translators and offering system-level advantages such as reduced system cost and increased flexibility. F521x and F522x devices also have a fast wake-up time at 3.5 µs and as little as 1.4-µA power consumption in standby mode, making them a great fit for “always on” sensor hub applications.
Sensor MCUs in health and fitness
MSP430 devices working in conjunction with sensors is now becoming widely popular in health and fitness applications such as activity monitors, pedometers and sports watches. The “always on” microcontroller reads various sensors and analog interfaces, runs computations/signal processing, provides user interface such as LCD display and keypad control and manages wireless/wired data transfer and connectivity interfaces.
MSP430 MCUs really shine in these applications primarily due to their ultra-low-power characteristics and ability to run for several months on a small watch battery. Furthermore, high performance analog and digital peripherals allow for flexible interface to sensors and AFEs.
At CES 2013, TI showed off a “health hub” watch featuring an MSP430 MCU. The health hub can monitor heart rate, body water content, oxygen saturation, heart rate, etc., and stream the data over a Bluetooth interface to a tablet.
Sensor manufacturer InvenSense recently announced the MotionFit™ wearable sensor SDK for health and fitness applications featuring the MSP430F5528 microcontroller and their MPU-9150 single chip gyroscope, accelerometer and compass.
That concludes this week’s look at sensors within MCU designs. Check back in next week where we’ll conclude this series with MSP430 use cases in wireless applications.
Download the MSP430F522x/MSP430F521x datasheet
Buy the MSP430F5528 now at Mouser Electronics
This post originally appeared in The Official MSP430 Blog on E2E.
For more Official MSP430 Blog posts, click here .
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