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iDAT: Web-Based Wireless Sensors for Education |
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DatesJanuary 2005 - December 2006 Principal InvestigatorsProfessor Ian Hunter (Department of Mechanical Engineering, Director of
MIT BioInstrumentation Laboratory)
ProblemImagine you are a curious student keen to tie the theoretical knowledge you have acquired in your undergraduate courses to real measurements. For example, you might be interested in measuring finger acceleration during piano playing, measuring the forces and accelerations involved in playing tennis, or measuring heart rate, peripheral body temperature, and foot-pedal force while riding a bicycle. This is currently extremely difficult due to the size and cost of most sensors and A/D hardware required to interface to a computer. The sensor leads often render these measurements impossible and are in almost all cases cumbersome. GoalDevelop a large set of high quality. yet low cost, miniature sensors and actuators that are wireless and contain their own rechargeable energy source (battery/super capacitor) for use in a wide range of educational settings including universities, high schools, science museums as well as for personal (home education) use. As we have developed the sensors and associated software environments, it has become apparent that simply providing students with a broad range of wireless sensors and asking them to "go forth and measure" is not enough. It is important to augment their free form measurement and analytic experience with structured experiments designed to reveal particular physical principles. The iDAT project has a secondary objective of creating a set of low cost scientific demonstrations that exploit our wireless sensors and enable physical principles and laws to be determined. In addition, it became clear to us that after having measured and analyzed some physical variables of interest students often want to control them. We have therefore augmented the iDAT project sensors (input devices) with the development of output devices such as wirelessly controllable semiconductor power switches, power amplifiers and actuators (e.g., vibrotactile, linear Lorentz force). The iDAT project has been divided into two phases. Phase I is devoted to the development of a suite of approximately 50 different types of very low cost iDAT sensors. Sensors will be field tested in the junior-level course 2.671, "Measurement and Instrumentation", taken by mechanical engineering students as well as those from physics and electrical engineering. In Phase II sensors will then be distributed to our collaborators around the world to demonstrate the impact of our wireless iDAT sensors as an educational tool beyond MIT. OverviewA problem frequently encountered in teaching instrumentation is that it is difficult to give the students significant experience in doing measurements in their own environment. This situation has improved by the recent commercial availability of compact, relatively inexpensive "smart" wired sensors and USB-interfaced analog-to-digital converter modules. In 2.671, "Measurement and Instrumentation", we provide the students with their own laptops and give them USB-based wired sensors for the first assignment, referred to as "Go Forth and Measure". In this experiment, students have taken data to answer questions of their own choosing, such as:
This assignment has successfully allowed the students to make measurements that are only limited by their imagination and the capabilities of the sensor. However, several students have felt limited by the wired nature of these sensors. One student measured the motion of her hand as she played the piano with a 3-axis accelerometer, and found the cord got in her way. Several other students wanted to use a 3-axis accelerometer with a bouncing ball, but again ran into difficulty due to the tether required between the sensor and the USB ADC unit. Finally, a student juggler examined the acceleration of a single juggling ball when juggled in a 3-, 4-, or 5-ball configuration. He found that the 5-ball configuration did not produce reliable data since other balls frequently ran into the sensor cord. The wireless iDAT sensors developed in this program will be hermetically sealed to allow even more innovative experiments to be designed - for example, measuring the temperature, pH, and conductivity of a liquid during a chemical reaction in a closed container or measuring body temperature, 3-axis acceleration, and heart rate during any exercise or activity, including swimming and taking a shower. The initial goal was to develop 50 different types of wireless sensors. Over 100 different sensors have now been acquired for the iDAT project. They cover all major areas of engineering and science. The constraints imposed by the iDAT project requiring low power small footprint devices dictated the selection of modern, state-of-the-art sensors mostly based on MEMS technology, new materials or new advances in technology such as new CMOS imaging sensors. In other cases, new sensors have been developed specifically for the iDAT project. These include a new force sensor using an innovative proven ring configuration with hall effect sensors and a micro-Kelvin temperature sensor. Our wireless sensor architecture is currently designed around the ARM7 STR7 32 bits RISC processor communication over the SPI bus with an Ember 260 Zigbee chip. The ZigBee 802.15.4 standard makes use of the international unlicensed 2.4 GHz and specifies a data transmission rate of 256kbps at a distance of 30m. Up to 256 devices can communicate directly over Zigbee. This represents a temporary shift from the initial iDAT orientation to system on a chip (SOC) devices integrating both Zigbee transmitters and processor on the same chip. This was necessary due to the difficulties that manufacturers experienced in the production and delivery of Zigbee SOC devices. While measurements are collected using the wireless sensors, students may use a wide variety of techniques to analyze the incoming data. These include function and model fitting (parameter estimation), signal analysis (e.g. power spectrum, autocorrelation function, probability density determination), and system analysis (e.g. linear and nonlinear system identification, dynamic model fitting). As an educational aid to understand sensors, 3D CAD models will be provided integrated either within the sensor itself or within the sensor documentation. These will allow to “fly through” sensors and simulate their operation. The software environment currently includes Mathcad, capable of numeric and symbolic computation, Unigraphics’ NX CAD system for displaying 3D finite element models of the sensor systems, and IGABUS, a signal and systems analysis environment developed for iDAT. Some extensions may be implemented for MATLAB, which is currently the prevalent software package used in Universities for data analysis. Over 1500 pages of Mathcad active lecture notes have been written for 2.671 and include a combination of numerical and symbolic computation. The iDAT documentation that will be provided with the scientific demos will draw upon these lectures and eventually converted to IGABUS active documents. The IGABUS software environment, designed from the ground up to take advantage of Microsoft Visual Studio 2005, Vista’s operating system including the Framework 2.0, the Windows Presentation Foundation, the Windows Communication Foundation and XAML. IGABUS will include a graphical editor for editing and manipulating mathematical expressions that are internally represented in Content MathML, which together with text, images, 2 and 3D plots, CAD models, videos etc are stored in Vista/WinFX/XAML form that is augmented with VB and C# code. Its computation engine includes both numeric and symbolic manipulation, and provides both an interpreter and seamless access to the common language runtime (CLR) system to incrementally compile and execute code thus reducing the computation time of the more complex algorithms by two orders of magnitudes over interpreted code. All of the algorithms developed in the frame of the 2.671 course are original, free of any copyright restrictions and to our knowledge error or bug free after years of intensive review, meticulous inspection and use by hundreds of students. They cover the most important areas of engineering and mathematics relevant to sensors and actuators including signal processing, probability theory and stochastic systems, error and uncertainty analysis, linear and nonlinear system identification, parameter estimation and modeling. Dissemination of iDAT SensorsWe currently have colleagues at a number of the world’s top universities (Oxford University, McGill University, University of British Columbia, University of Auckland, and Imperial College) who are looking forward to using the iDAT system in the second phase of the project. For the last few years, Prof. Hunter has been involved as a judge in the Massachusetts State Science Fair and has been struck by the limited use of sensors in the student projects. In general, he has found that students from the wealthy private schools tend to use more instrumentation in their projects. An essential goal of the iDAT program is therefore to create a suite of very low cost sensors, considerably lower in cost than the "low-cost" wired sensors discussed above which cost over $300 in a minimal configuration with only one sensor. An initial cost estimate for the iDAT system indicates that many of the sensors can be manufactured for less than $30 with no hidden costs, as we will be providing all software free. Even though colleges and universities spend more per student than secondary schools, budgets are nevertheless very tight, and our goal of supplying each student with a wide range of wireless sensors requires that the individual cost per sensor be as low as possible. However, the eventual dissemination of the iDAT sensors, actuators, demos and software will require infrastructure that we currently do not have and remains to be created and implemented. Publications
Presentations
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