Hand Hygiene

I have written some simple programs to test the digital input/output pins on the motes.  These will need to be used in our plans for modifying the door minders. The pins used are labeled GIO2 and GIO3 in the telos user guide. InputTest makes the red LED turn on if GIO3 is experiencing low voltage, and the blue LED turn on if it is experiencing high voltage.  OutputTest makes GIO2 alternate between high and low voltage every 2 seconds. CombinedTest (as its name implies) does both. Here is all the code

Note that each program is split into a configuration and a module file.

This a link to an IR encoder/decoder kit. The price range is $4-6, depending on how many are bought. This appears to be for transmitting coded information. We could possibly get one of these circuits working and see what happens when the IR wave is interrupted (i.e. someone walking through a door).

http://www.rentron.com/remote_control/TINY-IR2.htm

Developed a preliminary circuit schematic using EAGLE. Our goal is to eventually have this on one board, so both the encoder and decoder are together. Loose connections go to the mote, and are labeled so. In the original circuit, a Panasonic part, the pna4602m, was used for the IR detector. We already have the tsop36238, and will try using this in testing, as these are both detectors for 38kHz signals. Both the encoder and decoder chips use a 5V Vcc signal, but their operation under 3V (two AAA batteries) can be tested.

The ciruit does not work with the tsop36238, and the pna4602m requires at least 3.5 volts. Because the refrence voltage must be at most 3V, we are switching to the tsop32238encoder. This has a reference voltage that goes a low as 2.5 volts. Using a voltage divider with the pna4602m to cut this signal to 2.5V, the decoder circuit is still functional.

With the current circuit, as it is wired, the output period at the pins on the decoder is 54ms. Some pulses are a bit hairy, but when no signal is detected from the LED, the signal goes to constant high, or constant low. I believe the reason for the hairy output signal on the decoder is because the circuit is meant to send coded data, where here we are just using it to see if a signal completes.

On the encoder, the reference voltage the pins are plugged into is a square wave with a period of 14ms. The reason for the oscillationis because if plugged into a constant reference, the bit pattern will only be transmitted once, and we want it sent continuously.

We wondered whether it would be possible to detect a handwashing behavior with a wrist-mounted accelerometer. We bought an accelerometer, and did some preliminary testing. The accelerometer takes an input voltage of 2.2v to 3.6v. An input voltage of 3.3v was used for our testing. It has three output voltages which correspond to the accelerations on the x, y, and z axes.  The max/min acceleration can be set to +/- 1.5, 2, 4 or 6g (g being the acceleration due to gravity). For our test, this was set to +/- 1.5g. An output voltage of 0v means that axis is experiencing minimum acceleration. Zero acceleration occurs between 1.5 and 1.8v, and maximum acceleration occurs between 2.3 and 2.6v. All this data and more is available on the data sheet.

The accelerometer was attached to the wrist while performing various motions, and the output voltages were graphed over time.

Here is a graph when the accelerometer is standing still on the table top:

As you can see, there is a notable amount of noise, although the signal is still visible. The z axis is experiencing around 1g of acceleration since it is nearly parallel to the force of gravity, whereas the other axes are nearly perpendicular to the force of gravity so they are experiencing around 0g of acceleration.*

Here is a graph of the output voltages during vigorous hand washing motions:

Here we can see somewhat periodic fluctuations in the voltages. The output for less vigorous hand washing looks like this:

Here the fluctuations are less pronounced, but we still see a periodic trend (perhaps even more so). This information lends the accelerometer to use in the hospital. Accelerometers of this type could be put into wristwatch devices worn by doctors. After a puck is pressed, it could listen for a signal from one of these wristwatch devices, and if the trends in acceleration over a certain period of time match those of hand washing the puck would confirm that a doctor has washed his/her hands. In order for this to happen, however, a hand washing motion must have sufficiently different output from other motions the doctor may be doing.

Here is the output when the subject is idly swinging their arm:

Here we see a somewhat less pronounced periodic trend.

Here is the output when the subject is making emphatic gestures while talking:

This has potential to be confused with a hand washing motion since the magnitude of the fluctuations is similar to that of vigorous hand washing. This is particularly true if the gestures are repetitive in nature, resulting in a periodic graph. This case may be rare enough that it can be ignored.

Altogether, there are several things that must be dealt with for this application to be put into effect. For one thing, the motes would not fit in a wristwatch-size device. We would need to find something else which performs the same function as a mote, or connect the accelerometer to a pager through a chord. We would also need to figure out how to analyze the data quickly in the hospital. The setup used for this experiment involved one data point every 2-3 ms, resulting in about 10 kb/s of data flow.

At this point, more tests should be done on more people to determine if a hand washing motion has a predictable enough output. One possibility would be to put the accelerometer in a wristwatch device connected to a pager with a chord, and have a flash drive connected to the mote in the pager to store the data. This would allow us to collect data from the hospital to be analyzed at a later time.

*I use acceleration and gravity interchangeably here since we know from the general theory of relativity that the accelerometer won’t be able to tell the difference.

Force sensing resistors (FSR) may have useful application in the hand hygiene project.  A quick search of the internet revealed several companies specializing in force sensing resistors.  Outlined below are names of manufacturers, pricing, dimensions and other relevant information for a range of resistors.  Once the “puck” design has progressed, the required FSR dimensions may be more obvious.  Some of the prefabricated resistors listed below may fit our needs and be more cost effective.  Otherwise, custom orders can be made.

[iframe http://spreadsheets.google.com/pub?key=tidLdi8KmNBnVq1Wm_ktEWg&output=html 700 700]

Various tests have been performed on the alcohol sensor mq3. The device responds to the presence of alcohol in the hand sanitizers with an increase in output voltage. The response time is, however, very slow, and the source of the alcohol has to be no more than 1cm away. This was found by dispersing the sanitizer on the hands, and performing a “hand washing” motion for 5 seconds, and then placing the hand a distance on the ruler away from the device. The results for 1cm follow (using Google Docs Spreadsheet). The start/stop tags in the third column refer to when the hand was placed, and when the hand was taken away, respectively.

Test 1 Test 2 Test 3

For all the summary plots, the first point on each line notates when the hand was placed by the sensor, the second, when it was removed.

The results from the same experiment, except with the distance increased to 2cm follow. Because no noticeable results were produced, the distance was not increased.

Test 1 Test 2 Test 3

Experiments were also performed with the device taped onto the sanitizer container.

The first of these was performing a hand washing motion in front of the sensor (on the sanitizer container). Links to the raw data follows. The start/stop tags in the third column refer to when the hand was placed near the sensor, and washing motion was started to when it was stopped, and the hand was moved away. Although these tests did produce an increase in voltage, the delay between when the test was started to when this was observed was even longer than earlier experiments (with the ruler).

Test 1 Test 2 Test 3 Test 4

Because previous iterations with the hand just being placed near the sensor when it was placed at the end of a ruler produced results, this was tried when it was on the hand sanitizer. Data for these follows. Some tests show no increase in voltage, and others  do with a long delay.

Test 1 Test 2 Test 3 Test 4 Test 5 Test 6

This device does not seem suitable for our purposes because of its long response time. I believe it is meant to be used as a Breathalyzer, in which case the alcohol content of the air is more concentrated and directed into the device.