Hand Hygiene

In recent weeks, the development of the Polhemus project has come a long way.  We have been able to test the device and figure out how it works and have been creating programs in python in order to analyze the data we will generate from the experiment.  The following is a summary of how we propose the device will be used during this experiment.

The first leg of the project involved figuring out how the Polhemus device works and getting a feel for its limitations and its features.  After a lot of testing, we concluded that we would not use it for its actual coordinate positioning features because there was too much variance in measurements that were further than 6ft from the source.  We also felt that measuring each object in the exam room in relation to the source could become extremely tedious and time consuming, and also leave us with a lot of room for error.  The device did not have very good accuracy far from the source, but the measurements had high repeatability.  Because of this, we decided it would be best to use the Polhemus device to calibrate each object in the room.

We designed a program called calibration.py that allows us to map out different objects in the exam room, and save them as separate files.  The movements while calibrating replicate those of a regular motion with each of these objects, making sure to do these movements at every angle possible, and at every hand position possible, as not to disclude any possible movement.  Since these calibration files will be quite large, we came up with a cleanCalibration.py program, significantly decreases the size of the calibration files.  This program essentially takes the first point in the calibration file, draws a sphere around it with a radius of 1 inch, adds it to the cleanCalibration file, and tests the rest of the points in that file against the sphere.  For example, if the second point is inside the sphere, it gets discarded.  However, if the point is not inside the sphere, the second point gets added to the new cleanCalibration file and also gets a sphere around it.  The third point would then be tested against points one and two in a similar manner.  This program allows us to eliminate repetitive calibration points that slow down the analysis process.  With the addition of the clean.calibration file, we were able to reduce analysis time by about 75%.

The readPol.py program allows us to collect experiment data instantaneously from the PiMGR, which is the program that came with the Polhemus device and is responsible for collecting the motion capture data.  This program utilizes a pipe to take the information from the PiMGR, and writes it to a file.  This program produces one file per sensor, which means that we have the ability to do comparisons between the left and right hands if we so choose.

Preliminary analysis of the collected data is done with the closeToFiles.py program, which calculates the closest Cartesian distances between the raw files and the calibration files.  Those distances from each object in the room are calculated for each point in the raw data and are written to one master file.  The master file contains a column for each object in the room, and in those columns are the distances to the object at each time data was collected during the experiment.  The file also contains a timestamp, so we are able to tell exactly when the doctor was close to each object.

In order separate out the touches from the non-touches, the program touchSummary.py only takes distances from the master file that are 6 inches or less from any object and writes range of time for the touch to a file.  The summary is organized by object, with the time ranges and total touches under each object.  The total touches throughout the experiment are calculated at the end of the summary.  This program also outputs one file for each sensor.

At this point, we have done preliminary testing inside the lab and are ready to move to the experimental exam room in the hospital.  Future work might include a program that creates a timeline summary of the events during the experiment, which would make it easy to decipher what the doctor did during the exam and at what time, without actually being in the room.

Redesign Points:

1. Redesign the decoder portion to only trigger the MCU when the beam breaks instead of constantly telling it that there is a beam present. This is the main redesign goal as this is the cause of the large power drain.
2. Use a tripwire type design as seen here to determine if the doorway has been crossed. (http://www.instructables.com/id/Another-Arduino-Laser-Tripwire/)
3. Use a PIR (passive) to determine when someone enters or leaves a room (http://www.ladyada.net/learn/sensors/pir.html)
4. Using a 555-Timer in monostable mode would allow an LED IR receiver to be connected to the trigger line. If connected properly every time the receiver stopped seeing the signal from the LED then the 555-Timer output would pulse up to 5V for a time determined by C1 and then return to ground. (This is effectively acting as a 1 shot). This design uses a photocell to see when the IR stops receiving instead of a decoder. This would make the oscillation frequency of the IR irrelevant.
5. A 1Shot could also be used however the 555-Timer option allows for lower power than a 1 Shot.
6. Using a PLL would ensure that the mote was only triggered when the beam was broken but the PLL and the amplifiers to increase the signal all require dual power supplies. This could be implemented if a complete over-haul design process was warranted.
7. You could use an LED as a detector as shown below. Just use a small 5 mW red laser as the beam. Easily focused, low enough power ot not cause eye damage and will still allow the circuit to trigger. This will also “reset” itself once the beam is no longer broken.
8. Redesign the transmitter to have a current limiting circuit instead of current limiting resistors.
9. Redesign using a different encoder/decoder to draw less power. Or place an averaging circuit on the output of the decoder currently being used and set a thresh hold at which the mote would be triggered.

Each design has the potential to be lower power but depending on parts used, the size of the ducty cycle, power supply chosen and variation within parts the power will vary significantly. Digikey has several IR encoders and decoders with lower power applications. So does Mouser. The key to ensuring a low power design will be to actively monitor the power being used by each component.

Current Reciver:
22.3 mV – no beam: 17.1538 mA
19.5 mV – with beam: 15.0 mA
Max power: 55.2011 mW
Battery life: ~ 170 hours (7.3 days) to 130 hours (5.5 days) depending on how often the beam is broken.

The more the mote has to write the less the battery will last. This can be seen based on the RF transmit occur every time there is a break in the beam. This RF transmit causes a power spike of 121 mW to occur for a time. If the current draw on the mote was consistently at the power (3.188 V and 38 mA) then the battery life would only be 60 hours (2.5 days).

This points to the systems battery life being dependent upon the receiver instead of the transmitter. It also shows that the transmitter’s large power draw is occurring because of the RF transmission and flash memory write functions on the mote. As these functions are critical to the system developed and the end goals of the door minders it is not recommended to alter this portion of the design. The IR receiver/decoder also pulls a good deal of current while it is not receiving the IR beam, but it is significantly less than the mote and as the beam is only broken periodically, the average power draw off the decoder is low.

The test was started July 8th at 14:02.

The old design died at 23:27 on July 13th, lasting 5 days 9 hours.
The new design died at 16:00 on July 14th, lasting 6 days 2 hours.

Sam did the following research some time ago, but it was never posted to the blog. Her version is much nicer with formatting. Ultimately we bought one of the pico scopes and it is doing fine.

I have been looking into different audio level meters to be used to measure the volume in the MICU to determine whether or not the sound level in that area is high enough to cause problems for the patients when they are trying to sleep.

In looking at audio level meters, I have found three different categories which may be useful in our study. The first group can measure over a range of approximately 40 dB – 130 dB. This group has an approximate price range of $25 – $65. The second category measures over the range from 30 dB – 130 dB and have prices around $175 – $200. The final category measures approximately as low as 21 dB and up to 141 dB with prices from $ 2500 to $3133. The maximum of the range of any of these meters should be high enough for our purpose, but the minimum may not be what we need. On the next page is a list of 2 sound meters from each of the 3 categories, along with some specs and the prices.
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INTRO:

This post is designed to outline the functionality of the Door Minder as it is currently understood. As it is understood the system is powered by three batteries. There are three subsystems from the battery that use power, the 555 timer, the Tiny IR-II and the LED. The 555-Timer subsystem creates a pulse that drives the Tiny IR-II subsystem. This subsystem then drives the LED subsystem.

In Depth Details:

The 555-Timer is currently generating a 24 Hz signal in astable mode using R1 = 1k, R2 = 3M and C1 = 10n. On the rising edge of the 24 Hz signal the given channel line on the Tiny IR-II Encoder is pulled high. This triggers the Tiny IR-II to output a 38 kHz signal on the output line.

The output line on the Tiny IR-II controls a MOSFET, when the line on the Tiny IR-II goes high it turns the MOSFET on and in turn the LED. When the Tiny IR-II line is pulled low the MOSFET is turned off and in turn the LED is turned off.

POWER:

The power being pulled off the batteries by the current design is 21.21 mV RMS across a 1.3 Ω resistor. This is equivalent of 16.3154 mA. And a power draw of 78.34 mW from the 4.8 V produced by all 3 batteries. When the power across the individual systems was measured it was found that the total power from the individual systems was 78.5 mW which is within a 2% error. This error was deemed to be appropriate for the measures done.

Based on the battery data sheet, with a 16. 3 mA the battery should have approximately 200 hours of usable life (8 days).

Power After Redesign:

The power being pulled off the batteries by the redesign is 4.46mV RMS across a 1.3 Ω resistor. This is equivalent of 3.43 mA. And a power draw of 15.7 mW from the 4.7 V produced by all 3 batteries. When the power across the individual systems was measured it was found that the total power from the individual systems was 15.8 mW which is within a 2% error. This error was deemed to be appropriate for the measures done.

Based on the battery data sheet, a current draw of 3.43 mA will give a battery life of a little over 600 hours (25 days). This is at least 3 times the previous battery life.

Validation:

To validate the theory behind the change in design a model was made in MicroCap 10 and an analysis was run. The schematic is shown below:

The analysis was run by sweeping the value of the trim pot from 10 ohms to 500 ohms. The current and voltage across the diode was then graphed against the sweep. The output is shown below. Based on this graph the current and voltage will drop across the diode as the resistance is increased validating the data collected above.

Resources:

Tiny IR-II: http://www.rentron.com/remote_control/TINY-IR2.htm
555-Timer: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-1411-5-ND
Battery Life: http://www1.duracell.com/Procell/productdata/ (PC1500)

DNF, timeout, I/O and radio are errors I wrote, I think Bad sync must be something someone else was using. The first three are all errors which occur when attempting to program the mote, not sure about the last. I believe that we had lots of errors with the motes related to moisture infiltration of the ICs. If you attempt to replace any ICs on these motes, bake the components for 48 hours at a temperature of 125 degrees C before soldering them. In fact, bake the motes also before doing any IC replacement on them.

DNF = Device Not Found (i.e. did not appear in mote list).

Sometimes this is a problem with the USB connection. If you look at the telos schematic you will see that there are a few resistors between the USB connector and the USB/serial converter chip (FTDI). Check these connections with a meter. If they are all correct, your next target is the FTDI chip. First, use the schematic and a meter to ensure that you have ground and Vcc everywhere you are supposed to on the FTDI chip. If not repair the open circuit and try it again. If there is no power/ground problem the next thing I would tell you to do in a perfect world would be to check the resonator with a frequency counter to be sure it was working, but we don’t have anything which reads up to 6MHz. Next step is probably to replace the FTDI chip with a new one, and next the resonator. After that, if it still isn’t in motelist, your guess is as good as mine.

Timeout = Device appears in mote list but there is a timeout when trying to program it.

Suspect the processor. An interesting test would be to see if you can get the mote to program using the JTAG device in the TI box in the left cabinet. If you can’t program using JTAG, try reflowing the processor. If this still doesn’t work, assume the processor requires replacement, as JTAG is a direct line into the processor which is dependent on no other components on the board. If JTAG works but the mote still times out, follow the USB troubleshooting procedure above.

I/O = I think this was a separate error message which occurred when trying to program the mote.

Follow timeout procedure for lack of any better ideas.

Radio = Mote works but doesn’t pass radio test.

If the radio chip passes basic power and ground checks, bake up some CC2420′s and swap them in.

If all of the above fail, cast it in resin and use it as a really neat coaster for the lab. Keep in mind that there is a chance of fixing a USB problem only to find a processor problem, and/or fixing a processor problem only to find a radio problem.

Discovered by Ted:

http://www.youtube.com/watch?v=xiELOautbTI&feature=related

Very uplifting music, but no one gets under their nails.

Looks like there’s a whole series of them in the same place.

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.

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