Hand Hygiene

Project Overview

This summer we hope to extend the current hand hygiene study to the next phase, which will focus on the surfaces a doctor touches during a regular appointment with a patient in an examination room.  This study will focus on tracking what those touched surfaces are and analyzing how hand behavior might affect the spread of diseases in a hospital setting.  With the use of wireless motion tracking technology, we hope to be able to accurately study the hand behavior when a doctor is with a patient without interfering with the examination itself or infringing upon patient privacy.

We are looking for a wireless motion tracking system that requires minimal setup and calibration as well as easy to program software.  The system must be able to support at least two small sensors that will attach to the hands or wrists of the doctor.  The sensors must not be too cumbersome and they must have long lasting battery life.  We are hoping to be able to stay within the 10K budget.

Types of Motion Tracking Systems

After doing some research, it was clear that we had many different types of motion tracking systems to choose from.  We had initially thought that electromagnetic systems would be right for our application but agreed that we should look into other possibilities as well in order to see all the possibilities before making our decision.  Along with electromagnetic systems, we also looked into were optical and inertial systems.

Optical systems use data captured by multiple cameras from either active or passive sensors.  A computer is able to take the data from the sensors and triangulates the position of the object.  The optical systems we looked at utilized active LED sensors that are powered and are able to emit their own infra-red light.  Some advantages of a system like this is that that there is no interference with metal objects and the system is able to capture 6 degrees of freedom.  Downsides to this system is that they can become quite costly, and the data analysis can be quite time consuming.

Inertial systems use motion and rotational sensors that transmit data wirelessly to the computer where it is recorded to be analyzed later.  These systems require no outside references in order to determine orientation and position and they also allow for large capture areas, which can be useful in some applications.  However, these types of systems require a lot of analysis once the original data has been captured in order for the data to make sense.

Electromagnetic systems calculate the position and orientation by the relative magnetic flux of the coils on the transmitter and each receiver.  The sensors send out information in 6 degrees of freedom, which allows these systems to have a lower number of markers required than in optical systems.  These types of systems are simple to set up and calibrate.  Some systems are created in a way where they are not affected by motor noise, which can interfere with data collection.  A downside to these systems is that the sensors are susceptible to magnetic and electrical interference, depending on how close they are to objects like re-bar, wiring, cables and computers.

After researching the types of systems that were available, we narrowed our search down to six options, one was an optical system (MetaMotion PhaseSpace), two were inertial (InterSense Inertia Cube and  IS-900)  and three were electromagnetic (Polhemus Patirot, G4, and Liberty Latus).

Product Options

Polhemus Patriot Wireless

The first product we looked at was the Polhemus Patriot Wireless system.  This is a     wireless, electromagnetic system that comes with a hub, receptors and up to 4 sensors.  Each receptor has a range of about 8ft before the data starts to get inaccurate.  Each sensor has a battery life of about two hours before they need to be recharged.  This system is NOT affected by power grids or power motors, but does have some issues with metallic objects that are located near the source or sensor.

Cost: $8340.00

Polhemus G4

The G4 is Polhemus’s latest motion tracking product.  This is a wireless, electromagnetic system that comes with a hub, a source and up to 3 sensors.  The source is about the size of a smart phone and attaches to a belt loop.  The source give the system a reference frame for the sensor measurement.  Each sensor has a battery life of about eight hours before they need to be recharged and easily attaches to the wrist which can be seen in the photo above.  This system is NOT affected by power grids or power motors, but does have some issues with metallic objects that are located near the source or sensor.

Cost: $5850.00

Polhemus Liberty Latus (wireless)

The Polhemus Liberty Latus is a wireless, electromagnetic system that comes with a hub, a receptor and up to 12 sensors.  Each receptor has a range of about 8ft before the data starts to get inaccurate.  This product was designed for uses in large areas, and has the option of using up to 16 receptors at a time, and 12 sensors per receptor.  Each sensor is about the size of a key has a battery life of about two hours before they need to be recharged.  This system is NOT affected by power grids or power motors, but does have some issues with metallic objects that are located near the source or sensor.

Cost: $12,000.00

MetaMotion PhaseSpace

The MetaMotion PhaseSpace is a wireless 8-camera optical tracking system that comes with  8 cameras, an LED base station, a server computer, 40 Impulse Active LED, and an LED controller.  The cameras used in this sytem are cameras in name only, and are only able to pick up the LEDs.  the LED base station transceiver synchronizes the LED controller with the server.  The server computer outputs 3D position data with the option of using real-time remote motion capture.  Each active LEDs have their own ID are about the size of a dime.  They output infra-red light, but need to be seen in order to be picked up.   Each LED must be seen by at least 2 cameras in order to be tracked.  We would need at least 3 LEDs to track everything that’s rigid in the environment.  The LED controller is a radio frequency transceiver and can control up to 72 LEDs with a battery duration of 8-12 hours depending on use.

Cost: $20,000.00

InterSense IS-900 SlimTracker

The InterSense IS-900 SlimTracker is a wireless inertial-ultrasonice motion tracking device that utilizes an actual hand tracker.  The source can track up to 4 sensors at a time.  The system is immune to metallic interference and offers real-time tracking.

InterSense Inertia Cube Wireless

The InterSense Inertia Cube is a wireless inertial-ultrasonic motion tracking device that integrates nine miniature sensing elements.  The source can track up to 4 sensors at a time and the sensors are able to handle 8 hours of continuous use before the battery dies.  Heading calibration software compensates for static magnetic field distortions when using the product in adverse environments.

Product Specifications

https://spreadsheets.google.com/ccc?key=0AiXnOYF-JPATdE1naDRvem9ETzBCYXlPY0FPX3NpSVE&hl=en&authkey=CM_ajPwO

Product Recommendation

Based on the research on the three types of motion tracking devices and looking at each product individually, we feel that the Polhemus G4 would be the best fit for our application.  The G4 is completely wireless and will not hinder the doctor too much during the examination.  The sensors can be worn on the wrists and the source can easily be worn on a belt or in a pocket, since it is the size of a smart phone.  It is the newest of the three Polhemus systems we have examined and has the most up-to-date software and technology of the three.  Another important feature of the G4 is the long battery life.  A long battery life means a continuous flow of data throughout the experiment, which will save us time in the end when we analyze the data.  We plan on moving forward with this system in the next couple weeks.

(more…)

We’re getting a bit behind on the blog.  I just reinstalled Scribefire to make things easier again.  I also wanted to update a bunch of links that Ted has sent to me over the past month or so, so they are not lost:

4/12/11
If we ever need a mote-phone device …http://www.sparkfun.com/products/10585
This might be one way, building off the IOIO board.

4/10/11
http://sing.stanford.edu/swat/
I haven’t tried this myself, but it might be an interesting tool to measure conditions in
a clinic, hospital, lab, etc.  Didn’t read enough to know what hardware/software is needed.

3/15/11
http://blog.makezine.com/archive/2011/03/mini-home-fablab-for-around-4000.html
Well, not in a garage, but this is the modern update on the home workshop.

3/11/11
(not for Epidemiology/hospital, but just shows that lots of hardware/sensing can be thrown into the picture.)
http://www.springerlink.com/content/34568uu53758qg37/
We constructed informational support system based on massive sensor data in a room. In the room, called “Sensing Room”, approximate 600 sensors are distributed. Pressure sensors are embedded in a floor, a table, chairs and bed. Switch sensors and electric current sensors are attached on furniture and electric appliances. RFID tag readers are embedded into room planes. The room monitors human activities without restriction of occupants. Information support system includes steerable active projector on the ceiling. The projector displays information on all planes of the room. The occupant watch information wherever he/she exists in the room without restriction. Based on captured activities, information support system decides timing, position and contents fitting the occupants’ activities. In this way, massive sensors data achieves attentive support. We demonstrate notification, decision support and navigation by informational support system.

3/11/11
http://www.sensorsmag.com/product/wireless-mesh-radio-zmd
I’m not serious – about this being the new mote.  But, the general idea is out there.

1/16/11
While searching for papers about the tiny CC2430 SoC, I ran into this, which might be of interest to you (they use the same chip for their system). 
http://dcis2009.unizar.es/FILES/CR2/p31.pdf

1/16/11
http;//mobed.yonsei.ac.kr/~sukwon/paper/secon-cc2430.pdf
The above paper could be useful to consult along the way.  At least it will tell us how far others have gone, even if not TinyOS (it’s some weird Korean OS called RETOS;  at some point there was/is even a Korean company selling Telosb knock-offs, but the price was no better, so I never explored their platform).

I’ve spent some time getting acquainted with our noise monitoring friend and the possibility of interfacing a mote with it. The microcontroller and several other peripheral IC’s are encased in opaque epoxy, so this limits the depth of the analysis somewhat. There is a quad op-amp chip left exposed, however, which appears to be the heart of the sound level processing.

Signal:

IC4 drives the actual LEDs (encased). IC5 is the microcontroller (encased). IC6 is the audio driver for the speaker (encased). IC7 is the audio encoder for recording messages (encased). IC8 is an LM124 quad op amp. Two of the op-amps appear to be used as comparators, one which goes high if the yellow level is reached and the other if the red level is reached. The output goes to the microcontroller which is implementing a delay to avoid being triggered on single, short duration noises. The comparator outputs are NOT filtered in this way, and go high and low with each loudness event; more frequently than the device actually lights its yellow and red lights.

On IC8: Pin 7 is the yellow condition output and pin 8 is the red condition output. Both are positive logic with 0V as a 0 and 3.6V as a 1. Pins 5 and 10 are the amplified analog input which could be read by an ADC on a microcontroller to get real time relative sound level information. Pins 6 and 9 are the yellow threshold voltage and red threshold voltage respectively. These voltages increase logarithmically from 0 to about 3.8V as higher  dB thresholds are selected by the user.

The output to the actual LED’s can be taken as a “filtered” indication of yellow and red conditions, and would be the physically easiest signal to access. The yellow would have to be compensated for the fact that the yellow light flashes several times at each yellow condition. There would also need to be some form of buffer used between the LED outputs and the logic inputs. It may be possible to locate the “filtered” logic level signal, but this signal exists only on PCB traces and would be physically very difficult to utilize.

The audio input seems to be band pass filtered and sensitive to a 1.65 kHz tone, which I used for testing. My guess is that the actual center frequency is near to 200 or 400Hz and the filter is responding to the third or fourth harmonic at 1.65kHz.

Power:

The DC adapter puts out 9V, and the battery compartment seems to be designed to achieve this voltage with 6 AA’s. IC1 on the mode/record PCB attached to the back of the device is a 6V linear regulator which leads to a protected and regulated 5V power supply. This voltage leaves the small board and goes to the main board. It is labeled +5V at each end, either of which would be an ideal place to pick up power for a mote directly or via a 3.3V regulator.

IC8: http://www.national.com/ds/LM/LM124.pdf

A first piece of the development mote for the CC2431 has been assembled and successfully programmed with a blinky program using the same tool chain used for the TT2430 demo board we were working with previously. The CC2431.h file defines the location engine sfr’s and then just calls the CC2430.h, so with the exception of the location engine, the chip is in fact identical to the 2430.

And yes, I got the red and blue LEDs backward again… sigh

Above is a table summarizing the experiment conducted over the weekend in the hospital. “Expected angle” is the angle according to the ball bearing on the bed. The experiment was disrupted when the bed was put into use on Saturday around 8:00 pm. The sensor was retrieved on Monday, and the data collected.

The following is a link to the data collected

https://docs.google.com/leaf?id=0B2GN0bxAc29yMWM3M2Q4NjktOTY0MS00ZTU4LWJiNWUtNGY2ZDRjZjdlYzZj&hl=en&authkey=CKG0kp4I

Each data point is an angle measurement taken 10 seconds after the previous one. A value of 200 is recorded when the sensor is turned on, and a value of 222 is recorded when the sensor is calibrated. (Note that the data at the very end of the file, after the second power on was extraneous data taken in the lab ) These data are significantly different from their expected values because of a bug in the software which causes the sensor to loose its calibration if the power is cycled. (the sensor was turned off, then on again before the experiment).

Furthermore, there appears to be a time when the sensor stopped writing to memory, as we have no data after that time until it was taken into the lab. This appears to coincide with the time the bed was put into use (8:00 pm on Saturday). It is unknown what caused this. It could have been a faulty connection which was aggravated when the bed was moved. I don’t think it lost power, however, since it was on and flashing red when I retrieved it from Phil. (it toggles the red LED whenever the write to flash fails)

I have completed (but not yet tested) the generic front end module for the CC2420, so if anyone has a hankering to add 2.45GHz to their favorite microcontroller I can let you try one of these.

The successful working of the radio on the CC2430 mock-up has spurred increased interest in the smaller mote design. The direction of minimal size was chosen as this is really the greatest advantage of the platform.  I have been working on actually routing the second smaller mote concept. I have switched to a smaller crystal and in the end I had to resort to only placing a single LED. It won’t be as fancy as having three, but the single LED is still a valuable debugging tool. There is still some work to be done regarding the RF section. I am evaluating different antenna options as I would prefer a trace antenna over a chip antenna. If a sufficiently small 2.45GHz trace antenna can be found it will replace the chip antenna.

http://www.tte-systems.com/downloads/pttes_2010_07a.pdf

The following is a summary of my initial investigation into the Cortex M3 processor in preparing to work with the Atmel SAM3U Evaluation Kit. I have identified and located many useful pieces of literature on this processor.

Processor Core

The M3 processor is based on the latest version of the ARM processor core, ARMv7. In the past the various licensees of the ARM core would produce their own implementations for specific market segments. While this is still true, ARM has decided with v7 to try and improve interoperability between manufacturers by having 3 implementation profiles for licensees to choose from, and these are:

A – Application: These devices are based on a virtual memory system architecture and a memory management unit. This profile is aimed at high performance systems running full functioning operating systems.

R – Real-time: These devices are based on a protected memory system architecture and a memory protection unit. This profile is targeted at real-time operating systems and has optimizations for interrupt handling.

M – Microcontroller: From the ARM site: “The Microcontroller profile provides low-latency interrupt processing accessible directly from high-level programming languages. It has a different exception handling model to the other profiles, implements a variant of the PMSA, and supports a variant of the Thumb instruction set only.”

In working with the Atmel SAM3U, we are working with an ‘M’ profile of the ARMv7 processor core. There are a few important reference documents from ARM regarding this architecture:

ARMv7-M Architecture Reference Manual

Cortex-M3 Technical Reference Manual

Cortex-M3 Devices Generic User Guide

There is a possibility that all three of these could be contained in a zip here.

Device

The Atmel implementation of the ARM7-M is the SAM3 series of processors: SAM3N, SAM3S, and SAM3U. The SAM3U has been identified by the TinyOS community as a primary target for next generation devices. The SAM3U4E is the processor available on the SAM3U Evaluation Kit, and is therefore the processor we have available for use in the lab. You can find the data sheet here.

Some additional documents from Atmel:

Getting Started with SAM3U Microcontrollers

SAM3U-EK User Guide

These and other documents and development resources can be found on the SAM3U-EK page.

A little light reading, and we’ll be on to coding.

The progress with the CC243x devices got me interested in what could be done with them in terms of actual physical devices. I did some research and mocked up two concepts for a “smaller mote” based on a CC2431.

Concept 1:

Concept one is optimized for performance, but is smaller than the telos at about 22 x 49mm. It runs on two 10mm coin cell batteries and is non-rechargeable. The antenna is a balanced folded dipole from a TI application note. TI claims that the range of this antenna and this chip in combination is 300 meters. There are 3 LEDs and a reset button, and also room to add another peripheral or two if needed.

Concept 2:

Concept 2 is optimized for size at 12 x 33mm. I’ve used a balun and chip antenna to minimize the RF path. There is a single non-rechargeable 10mm coin cell on the back side. Again, the three LEDs and the reset button are present, although here I think it would already be a significant challenge to route this thing without adding extra peripherals. RF will suffer a few db from the balun and the chip antenna, but I think this is a good concept of what the limit of miniaturization would be with the CC2431.

Then again, if we didn’t bother with voltage regulation and skipped the LEDs and buttons… Well, maybe we could get a little smaller.