Hand Hygiene

I did another battery test using a modified version of Ted’s code which makes the pagers broadcast their battery readings, and turn off automatically at a reading of 1600.  The modified versions of sampADcC.nc and sampADcP.nc can be found here:

http://docs.google.com/Doc?docid=0AWGN0bxAc29yZDdqZG5zd183aGI4bWgyZjk&hl=en

http://docs.google.com/Doc?docid=0AWGN0bxAc29yZDdqZG5zd182ZnZ2cXpnZzU&hl=en

The following table and graph summarize the data

The motes exhibited some strange behavior after the test. mote 244 ended at a reading of 1607, which should correspond to a voltage of about 2.5v. When I measured the battery voltage, however, it read 3.2v. I turned it on again after the test, and it broadcast a reading of around 1980, which sure enough corresponds to 3.2v. I’m  certain it was not plugged in between the time the test ended and I read this voltage. In the last test, both motes exhibited the same behavior, but I let it slide since they had been plugged in for some time (1-2 minutes) before I checked their voltages.

Both of the other pagers in this test had a battery reading of 0v, suggesting the automatic shut down didn’t work for them, and they drained their batteries overnight. The test results seem to suggest they turned off at the right time, however, and I don’t know why the automatic shut down would work for one pager but not the others.

I did a quick experiment to find out how close the settings of the puck need to be adjusted for it to record data properly.

I started with the screw in so that the pushes could not be recorded. I recorded the start linux time and the finish linux time for each trial. During the trials, the gel sanitizer was pushed ten times with a one or two second gap between presses. After each trial, the screw was adjusted a quarter of a turn.

The first two trials showed that the puck was not activated at all. The next four showed that the puck was pretty much activated when it was pushed. (There was one dispenser press where the puck was not activated, but that could have been not pushing hard enough.) The seventh trial showed that the puck was activated by some of the presses, but it also stuck between presses. In the eighth trial, there was one activation where the gel sanitizer was sitting on the puck so that the pressure pad was always stimulated.

What I found was that the screw needs to be adjusted to within one turn to give the proper readings.

Data for each individual trial is at: http://spreadsheets.google.com/ccc?key=0Ajml4qs0jKAXdHY0aUw2TkFBNFlhOGQ4NS00bWg3NWc&hl=en

Re-inserted the 7mm antenna into the puck mote, and ran tests on the 8-mote rig. Here is the boxplot and CDF. The CDF seemed to be good for 1m (centered at 0).

Here are the results from the 2/13 test. The False positives and false negatives on the foam trial are probably due to difference in set up between the 2 experiments.  Note that there is some debate about the number of misses in the foam trail — it might be twelve.  Also the extra hit represents a button press of less than 1 second, which is probably switch bounce — Ted’s code filters such quick double hits as noise.

From the data recorded by the puck, we took out the heatbeat data and the puck released data. Using just the presses, we subtracted the time recorded from the next data point to get the differences between presses. Between trials, we pushed the puck repeatedly to signal between trials. Then the puck was pushed once more to signal the start of the trial. Approximately 30 seconds later, the trials began. There is some discrepancy between the times recorded by the person and the times recorded in the mote data set. It seems that we recorded data points for a longer period of time than the mote recorded.

http://spreadsheets.google.com/ccc?key=0AkDR_-NeZVpydDAwWmx2eFlpN1lkX3ZoWDlMdTJMd0E&hl=en

Trial 2: Compares our data with puck data

http://spreadsheets.google.com/ccc?key=0Ajml4qs0jKAXdGxvR090OVFWalY3WGs0c3M5X3F1SHc&hl=en 

- Deepti & Arunan

I did another battery experiment today. A voltage source was connected to the pins in the front of the mote (the pins that connect the plain motes to AA batteries). 3 green motes (the ones we are currently using), and 3 blue ones (from the old pagers) were used in this experiment. The motes broadcasted their voltage readings, and a mote with Basestation received them. The data points here are averages of about 20-25 readings for each mote and voltage level. The code used on the motes was the PuckToRadio code from the PagerTesting directory. The code can be found here:

http://docs.google.com/Doc?docid=0AWGN0bxAc29yZDdqZG5zd180ZGJkcjRrZmI&hl=en

http://docs.google.com/Doc?docid=0AWGN0bxAc29yZDdqZG5zd18zZm5rc3Y5aGs&hl=en

http://docs.google.com/Doc?docid=0AWGN0bxAc29yZDdqZG5zd181Z2pnc21nNXY&hl=en

Here are the data:

I ran a quick, informal experiment to confirm the characteristic of the Interlink square FSR that we currently have. I fixed the FSR to a firm surface, placed a square acrylic block of variable surface area on top, and measured the resistance of the sensor with variable weight applied. I made a few significant findings: the FSR’s are sensitive to pressure rather than pure force; at some point in their response range, the two measurements converge (for example, a 500g weight applied over 9cm^2 gave roughly the same resistance as the same weight over 4cm^2, while 200g over 9cm^3 gave roughly 1.5 times the resistance as the same weight over 4cm^2); I confirmed the minimum threshold described in Interlink’s datasheet (the 50g weight over 16cm^2 left the sensor open, while the same weight over 9cm^2 gave resistances on the order of 20kOhm); there is a considerable amount of lag time and drift associated with the measurements. In fact, the drift was so significant that during some measurements the resistance seemed to almost continually decrease (for example, from 45 to 15kOhm over 20 seconds). In other cases, the resistance stabilized to (surprisingly consistently) -10% of the initial value after approximately 5 seconds. If I am reading the datasheet correctly, this is inconsistent with the specifications given of +/-2-5% part-to-part repeatability and a mechanical rise time (?) of 1-2 milliseconds.

These measurements may be attributed to experimental error, multimeter (Fluke) sampling, or hysteresis (something I don’t have the knowledge to comment on but is mentioned in reference to these devices), but I think they are significant enough to warrant further investigation.

The confirmation that the devices are pressure-sensitive will greatly affect their design intent: we will have to pay close attention to how we actuate them with respect to delivered pressure and saturation point (upper response threshold).

One of the main features of the new puck design is to incorporate a force sensitive resistor to bypass the use of spring (which requires calibration/tuning). Ideally, we would like to use a component that:

• is available in a wide variety of shapes and sizes
• is force-dependent rather than pressure-dependent
• has a linear relationship between resistance and applied force
• has a dynamic range appropriate to our application
• is relatively low-cost

An FSR that is force-dependent rather than pressure-dependent implies that the behavior of the component is not influenced by the footprint of the force acting on it. This means that the component could be used in a wider variety of applications, as we do not need to be concerned with how we are actuating it.

An FSR that provides a linear relationship between applied force and resistance may ease signal processing. This is speculative on my behalf, because I don’t know enough about the signal processing that would be required to essentially turn it into a reliable programmable switch.

The FSR’s produced by Interlink have a response characteristic that is described in this datasheet. To paraphrase the datasheet, the high end of the dynamic range is marked by a ’saturation point’ at which the decrease in resistance with respect to increased force (more specifically, pressure) tends to zero (in other words, how much pressure is applied before the sensor quits sensing). Therefore, the saturation point must be at least equal to the maximum pressure we would apply in application, but too much, and we lose resolution. The Interlink datasheet quotes a saturation point on the order of 100-200psi. I have roughly estimated the force to actuate the Avant/Avagard sanitizer bottles to be somewhere around 39-59N (8.8-13.3lbf). If we assume that a nurse in a hurry might apply up to 25lbf to the pump, the minimum sensor size to avoid over-saturation is 0.25in^2. Interlink offers three premade FSR’s: 4mm diameter (~0.01in^2), 0.5″ diameter (~0.79in^2), and 4×4cm (~2.5in^2).

Davie had much more luck with sourcing than I did. Initially, I only found “good” technical information from Interlink, but outlined in the blog post below are other sources that Davie found:

http://static1.shopify.com/s/files/1/0010/4352/files/Electrotap-t303c.pdf

http://sensitronics.com/characteristics.htm

http://www.tekscan.com/flexiforce/specs-flexiforce.html

It seems that, for the most part, the FSRs available from these manufacturers have comparable size/shapes (4-12mm diameter round, 0.5-1.5″ square), response ranges (1-150psi), and prices.

http://spreadsheets.google.com/ccc?key=0AkDR_-NeZVpydGp2SEctcXk5WWN6Nmh3TTR3WnlpWWc&hl=en

Experiment Date: 2/13/10

Start Time: 1:57:57

The aim of the experiment was to check the proper functioning of the mote and the pucks. The experiment was organized in such a way that the user performed a hand sanitizing event, walked into the room for approximately 15 seconds, came out and performed hand hygiene again, and waited again for 15 seconds before repeating the same.

The experiment was set up in a manner that the sanitizer when pressed would stimulate the puck and the readings were collected by the mote on the PC through the program PuckToRadio. The data was also recorded manually in order to keep track of the readings. Once the results were collected, the data generated by the mote was compared to the data obtained by the user.

Analysis:

For the first experiment using gel sanitizer, the data generated by the mote seemed to be in correlation with the data collected manually. A scatter plot was generated between the two data sets and the estimate was to see a linear trend in the experiment. Once the linear trendline was set up, the correlation constant (R ) turned out to be .9663 which indicated that the data sets generated by the mote and collected manually were in close proximity and followed a linear trend.

We calculated the difference between the two times generated by the Linux machine, of which the last five digits correspond to the milliseconds of the actual time. We divided the difference by 1000 to convert from milliseconds to seconds. We set up a relative point after which we calculated the difference between times recorded by us in seconds. The data for the same is shown in the table below.

For the second experiment using foam sanitizer, the data generated by the mote did not correspond to the manual data sets. The number of clicks recorded by the mote was lesser in number when compared to the ones recorded by us. The data set is linked below.

From results through the second experiment, we can hypothesize that the mote has problems sensing the signals when foam sanitizer is used. This may be due to the fact that the pucks do not respond in the same manner as they did when gel sanitizer was used. We noticed that the difference in seconds between two presses recorded by the mote differed by the sum of a few of our data points. This tells us that some data points have not been recorded by the mote. We could fix this by adjusting the physical set up of the puck to match the type of sanitizer being used, since we did not change the set up when switching from gel sanitizer to foam.

Deepti and Arunan

(links to come later tonight 2/18)

A battery test was done using Ted’s new code for the pagers. The following table and graph summarize the data.

Another test was also done with a pager connected to a voltage source to find out the relationship between the battery reading broadcast by the mote and the actual battery voltage. The results are shown below.

As the trendline indicates, the battery reading is about 600 times the battery voltage. The voltage that is acutally being measured is 10/26 of the battery voltage (not 1/2, as it used to be).  The code should probably be modified so that the motes shut off when their batteries are around 2.7v, or a battery reading of about 1700.