Hand Hygiene

I am working on testing anchors to find a drop off that would be good to measure near patient/far from patient.

I did the tests on the old and new anchors ranging from .5 – 3 meters away (in steps of .5), from 0 – 180 degrees (in steps of 20), both vertically and horizontally oriented.

(BRUB = .5 m, KI3U = 1 m, KICX = 1.5 m, BSK1 = 2 m, BS7K = 2.5 m, BSIX = 3 m)

Here are the Cumulative Density Functions from the data:

The new anchors, horizontally oriented gives little distinction for us to use for near patient/far from patient.

Using new anchors, vertically gives us better distinction in the middle range.

Using the old anchors, horizontally oriented doesn’t give us the distinction between near patient/far from patient that we’re looking for.

From the CDF graphs, we can see that the old anchors, vertically oriented gives us the best distinction between near patient/far from patient, but this could be improved. We would want better distinction between 1 and 1.5 meters. Also, we want a higher RSSI peak within boxplots per angle, so that there would be an area around the bed (oval-shaped) that would count as near the bed and everything else would be far from bed.

Background:

The test circuit was designed to test the capabilities and limitations of the newest of the transfer methods that utilized a photoresist. The positive photoresist is an additive to a traditional PCB in the manufacturing process or is available (for lower quality applications) as a separate spray or film. The photoresist is a chemical compound that reacts to UV light and dissolves in a developer solution, similar to developing photographs. The objective of this test circuit was to determine overall limitations of the process of drawing, printing, transferring, developing and etching a circuit board designed in-house. The PCB tested several aspects that would be necessary in determining limitations of PC designs such as:

1. minimum trace widths

2. minimum trace separation

3. minimum/maximum trace width:length ratios.

Determing these key aspects of the newly designed PC manufacturing process would allow the engineering team to develop a steadfast set of rules by which all following PCB’s must follow.

PROCEDURE:

In order to maintain consistency and minimize errors as well as confounding factors, the current procedure was developed for use of POSITIVE photoresist (through several runs of trial and error). In order to accomplish these sets of tasks, I developed a makeshift PC holder for the exposing stage of the procedure.

Many procedures call for a piece of thin, yet heavy, glass or crystal to lay over the PCB while it is exposing. However, as the team did not have access to any sizable amounts of glass or crystal, we developed a 4” X 4” containment made up of two pieces of plastic. One side was made of a black, opaque piece of plastic. The top piece, identical in size and shape, was made of clear acrylic. Both pieces had holes drilled and tapped into them so as to allow the pieces to compress the PCB and the transparency/paper together. Additionally, it is important to make sure that the clear acrylic allows light (and UV) to evenly pass through onto the paper and, ultimately, the PCB. Once this was made, the procedure for making the PCB could follow.

1. After designing a proper board (one that does not violate any conductive or developing rules), print a MIRRORED image of the PCB layout, actual size. The printout should print only where traces are needed; blank or empty places on the printout will eventually contain no copper and be completely etched to the fiberglass under layer. This can be done either with a transparency or a piece of paper.

2. While in low-UV light (in the presence of an incandescent is preferable) remove any protective covering from the PCB and place it on the opaque containment backing, with the photoresist facing up. At this point it is important to ensure that the PCB is both free of foreign materials (dust, dirt, etc.) and is perfectly flat (i.e.- no burrs or deformities that would prevent the clear acrylic from compressing the entire paper/transparency to the PCB).

3. Place the transparency/paper INK SIDE DOWN on the PCB so that all desired traces and features are on the PCB. Placing the image face-down on the photosensitized PCB allows for the closest possible contact between the printed image and the UV-sensitive PCB. Placing the ink side away from the photoresist could allow for inadvertent light exposing underneath the traces and features, which would create a blurred image and possibly (in the case of thin features < 0.005”) create a line too thin to be properly etched.

4. Secure the image and PCB by placing the CLEAN acrylic piece on top of the backing and secure with screws or other appropriate fasteners. Ensuring a clear piece of acrylic ensures the cleanest and most accurate transfer of the image. Dirt or dust particles on the acrylic can have adverse effects on the development of the image on the PCB by leaving an image in the photoresist of that particular particle.

5. Once secured, expose the light to UV light. Because of availability of resources, the research team used a grow-light (used to sprout and grow plants) with an exposure time of 5 minutes. In order to ensure even exposure and minimize the effects of any shadowing or uneven exposure, I turned the entire containment 90 degrees about every minute or so.

6. Once the PCB has been exposed for an appropriate amount of time, take the entire board out of the containment device while in the presence of low-UV light.

7. Add the PCB to a developer solution until the appropriate features and traces are the only visible portions on the PCB. When using paper as a transfer medium, initial (<15 sec.) developing will reveal a dark square where the paper was present over the PCB, while the traces and necessary features will be only slightly visible. Keep agitating the developer solution until only the desired features and traces are visible. This could take from 30-90 seconds, depending on thickness of paper, exposure time, and complexity of the transferred image. Additionally, the developing solution and container were a simple mixture of 1g NaOH / 100 mL H20 in a glass beaker (large enough to hold the entire PCB). Developing the image requires the PCB to be submersed in the solution. Furthermore, the solution may be reused several times (5-10) before requiring disposal.

8. Immediately after developing the image on the PCB, immerse the board in water to stop the developing process. By not properly rinsing the solution off the PCB, the developer still dissolves the photoresist and can possibly dissolve necessary traces and features.

ETCHING:

1. In a glass beaker, add an appropriate amount of water necessary to adequately cover a fully submersed PCB.

2. To this water add Ammonium Hydroxide in a concentration of 3-8 g/ mL water and fully dissolve.

3. Add the developed PCB to the solution stirring frequently. Depending on the concentration of the solution as well as the size of the PCB, developing times range from 45-200 minutes.

4. Once all unwanted copper has been etched away, fully rinse the PCB to stop the etching process and remove the etching chemical. Because of the environmental as well as health-related impacts of ammonium hydroxide, all solutions and waters contaminated with this compound need to be properly disposed of. Handling and disposal of the compound requires proper glove and possibly respiratory protection as the chemical is an organic oxidizer. Disposal of the solutions requires all liquid contaminates be absorbed by means of paper towels or other disposable sponges and contained in chemical resistant plastic bags. All rinsing liquids and solids in contact with the ammonium hydroxide solution need to be disposed of in a similar fashion. Only after these agents and chemicals have been properly sealed can they be disposed of in the garbage can.

5. With the rinsed and dried PCB (now fully etched), dip or rinse it in an acetone in order to remove any inks, marks, or photoresist that remains. After cleaning with acetone, rinse the PCB a final time in water and pat dry. The remaining PCB should be complete and ready for use.

RELEVANT TERMS AND DEFINITIONS

Photoresist – A compound, either dry film or spray, that reacts to UV light. Positive photoresists are resists that weaken when exposed to UV light. The result is that exposed areas dissolve in a developer solution and unexposed areas don’t dissolve (or as quickly). Negative photoresists are resists that strengthen when exposed to UV light. Using a negative photoresist requires all traces and desired PCB features to be represented on the transparency/paper as blank or white spaces; all black and filled spaces will eventually be dissolved away by the developer and ultimately etched away.

Photosensitized – Having a photoresist present on a PCB. Exposing a photosensitive PCB to UV light without proper protection (usually present when pre-sensitized boards are ordered) will inadvertently ruin the photoresist.

Etchant – A solution that is used to dissolve away the copper layer of the PCB. The etchant used in this process was a highly corrosive substance known as ammonium persulfate. However, a more common etchant used in home manufacturing of PCB’s is ferric chloride. Benefits of using this solution are that it is slightly faster than ammonium persulfate and it is less toxic. However, because of the nature of ferric compounds, the etchant is very staining and more difficult to clean up. Ammonium persulfate is a very toxic substance that has ecological impacts in addition to those discussed in warnings. As a result, more care must be taken to decontaminate the etching site than with ferric chloride solutions. However, ammonium persulfate can be beneficial in etching small, intricate PCB’s as the etching process will not occur too quickly to properly gage and control the process.

FINDINGS

As a result of running this “test,” we concluded several things regarding the tolerances and limitations of the photoresist and ammonium persulfate procedures. Positive results include: accurate surface mount transfers, minimal trace spacing and minimal trace width. Negative results include: inadvertent etching and lack of trace separation.
Of the negative results, the most prevalent was the inadvertent etching of the ammonium persulfate solution underneath the outlined traces. This result was most prevalent in the traces that were narrower than 0.003”, but some cases were present in long traces of 0.006 and 0.005 inches. Further research and experimenting would need to be conducted in order to determine the reason for this occurrence. However, discussion speculates that traces run the risk of over etching if they are overexposed to etchant. In the test board, this overexposure time was anywhere from 60-120 minutes beyond the time in which the traces were adequately etched. This overexposure time was a direct result of having a large, square PCB. While the smaller traces, drawn near the outer edges of the board, were properly etched away, the etchant had not etched the middle portion of the board. This is most likely because there was a thin ( < 1” ) layer of etchant solution above the surface of the PCB. Yet, around the edges, because of the shape of the beaker, there was a greater amount of solution. Additionally, in attempting to lessen these differences in solution locations, the liquid was agitated and stirred frequently. It was at these agitation times in which pieces of the hardened photoresist (blocking the etchant) detached from the PCB and allowed the etchant to dissolve through the desired traces.

Similarly, as the traces were frequently overetched, sometimes thin traces melded together. This was a result of placing thin traces too close together. When traces were placed within 0.005” of another, the results were simply a wider trace that shorted out the two smaller traces. Additionally, traces spaced at least 0.010” apart had no shorting or showed any inadvertent bridging with other traces.

Positive results of the experiment concluded that the photoresist and chemical etchant process had a successful transfer for larger, yet realistic, traces. All traces at 0.016” widths had perfect transfer rates and had no occurrences of overetching or bridging/shorting. With the smaller-width tests, successful transfer rates drops off considerably, but with certain patterns that can be useful in future PCB designing. Traces of 0.006” had a moderately high transfer rate. The vast majority of traces ( >70%) of this width experienced no overetching. However, as evidenced with the small traces, placing the traces too close ( within 0.005” ) to another caused bridging and exceeded the resolution of the overall process. Traces of 0.005” width had similar results. While a majority of the traces of this width experienced little or no overetching, some traces were bridged (if placed within 0.005-0.007” of another trace) and others were overetched. The most common trait between all traces (of 0.005” width) that were overetched was that they were all widely separated from another trace ( > 0.02” ) and were fairly long traces ( > 1.25” ). Traces that were bunched together, but not below the resulting spacing threshold, and not exorbitantly long had a nearly 100% successful transfer rate.

A more controlled experiment was conducted to test the response of the force sensitive resistors. In this case, force was applied to a sensor (FSR + rubber buffer) using a hinge mechanism. The experiment tested the effect/variance of the resting height of the hinge lid on the sensor, the force applied to the lever/system, and the (binary) distance from force application to the fulcrum. For each combination lid height and distance to fulcrum (measure at the ‘front’ side and ‘back’ side of the sensor), three measurements were taken: one each at approximately 1kg, 3kg, and 6kg (hand washing pump force is likely to be 3.5-4.5kg). Statistical data has been compiled and is presented below as an ANOVA general linear model. In this instance, the force applied is represented in Kg, the distance from the force application to the fulcrum is represented by ‘f/b’ (1 being the side of the sensor closeset to the fulcrum), the resting height of the lid is represented by the categorical ‘lid’ variable — in position 0, the hinge lies at a lower height than the sensor, in position 5 the hinge lies at a lower height than the sensor, and at position 3 they are roughly at the same height. each position is approximately 0.3″.

General Linear Model: ohm versus lid, f/b 

Factor  Type   Levels  Values
lid     fixed       6  0, 1, 2, 3, 4, 5
f/b     fixed       2  0, 1

Analysis of Variance for ohm, using Adjusted SS for Tests

Source  DF   Seq SS   Adj SS   Adj MS      F      P
kg       1  3602646  3609772  3609772  38.93  0.000
lid      5   308095   305901    61180   0.66  0.657
f/b      1   799933   799933   799933   8.63  0.007
Error   28  2596131  2596131    92719
Total   35  7306805

S = 304.498   R-Sq = 64.47%   R-Sq(adj) = 55.59%

Term         Coef  SE Coef      T      P
Constant   1034.3    103.5  10.00  0.000
kg        -155.52    24.92  -6.24  0.000
lid
0           -33.8    113.5  -0.30  0.768
1           -73.0    113.6  -0.64  0.526
2           -72.9    113.6  -0.64  0.527
3           -33.1    113.6  -0.29  0.773
4            18.2    114.8   0.16  0.875
f/b
0         -149.30    50.83  -2.94  0.007

Unusual Observations for ohm

Obs      ohm      Fit  SE Fit  Residual  St Resid
 25  1805.00  1040.10  143.29    764.90      2.85 R
 31  2210.00  1269.33  154.55    940.67      3.59 R

R denotes an observation with a large standardized residual.

This data suggests that it is highly likely that the force applied and the distance from the force application to the fulcrum are good predictors for sensor resistance. This makes sense. More insightful is the suggestion that the resting height of the lid is not a good predictor for sensor resistance (suggested by the correlation coefficients of the lid variable). The R2 value for this analysis seems reasonable enough with only 36 data points.

This scatterplot illustrates the difference in sensor response at two different locations (the left panel at the ‘front’ of the sensor, furthest from the fulcrum, and the right panel closest to the fulcrum). The right scatterplot indicates generally the type of distribution we would like to see, but with some sort of characteristic in the force range we would like (3.5-4.5kg). The left scatterplot represents desirable low variance.

On Thursday I will perform another test that does not vary lid height, continually varies fulcrum distance (rather than taking only two measurements), and takes more continual forces in the range that we are concerned with. If these results show enough promise, the hinge design will be confirmed at more vigorous work can be completed on this puck design.

Ted sent along this handy hint:
http://blog.synthetos.com/how-to-make-an-eagle-solder-mask-stencil-for-an-laser-cutter/

We ended up having to copy everything in the home directory from the maintenance terminal to an external flash drive, and doing a clean install of Ubuntu 9.10 (the CD is currently on top of the TinyOS computer tower… make sure it is v9.10, not v9.04) We copied everything back over from the USB drive, and reinstalled the TinyOS runtime environment. The instructions for reinstalling TinyOS are laid out very clearly on this website:

http://docs.tinyos.net/index.php/Getting_started_using_Ubuntu_9.10_and_TelosB_motes

Note, this is for only i386 processors. This will not work for the Unix machine on the southeast wall, as it has an AMD x64 processor (I don’t think the debian package is included with x64).

Also, if an error comes up about a problem with tinyos-tools, go into synaptic (System>Administration), and install it. This gave me a dependency error, something about having to override items in nemerle. I uninstalled nemerle, and everything worked fine.

Finally, I believe we will only be able to get eagle to work on the AMD x64 machine, as the packages installed on the i386’s aren’t compatible, and there doesn’t seem to be a way to update them without errors.

Preliminary test results in a mock FSR sensing setup are promising in some ways. The first test setup was the FSR blanketed by a 1/8″ rubber sheet compressed under a disc that is pin-guided on top of the bottom disc. Fairly static loads were applied at different points over a wide area on the load-bearing disc and corresponding sensor resistances measured.

The primary purpose of this test is to determine a baseline correlation between applied force to the test mechanism and output/sensor resistance.

The secondary purpose of this test is to determine whether or not our mechanism will provide sufficient clarity to discern between completely downward forces (eg, someone pressing straight down on a bottle), or partially ‘torqued’ forces that create uneven pressure distribution at the sensor (eg, someone pressing down and slightly pushing back on a bottle).

In this particular setup, the primary purpose is explored by this plot of applied force vs. resistance. A 3rd order curve has been fitted to the data, giving R2 on the order of 0.80. Under illustrated confidence/probability intervals, it may be inferred that we could, for example, tell fairly reliably the difference between 2kg  and 5kg load. (In rough testing, I found that the average hand pump will fall somewhere between 3.5-4.5kg — but further consideration is due).

The secondary purpose seems to have been satisfied: after taking approximately 80 measurements over different forces and displacements, and fitting these as predictors of resistance, applied force is much more correlated to resistance than position. (((f-test values?))

To be taken into consideration: we need a better construction of our intended model. Although, by indication from position testing (if I am interpreting the data analysis correctly), the pin mechanism to relieve torques may not be as important as previously perceived. Worth exploring differences between rubber materials and/or FSR sizing/geometry.

I was attempting to install Eagle 5.7.0 on the TinyOS computer through http://packages.ubuntu.com/. This website downloads self-installing packages to the computer. The installer for eagle complained about the version of libfontconfig1 being out of date, so I downloaded a later version of that, and attempted to install it. This complained about libfontconfig1-dev being out of date. I downloaded this package, and attempted to install it. This complained about libfontconfig1 being out of date again. I used Sympatic package manager to uninstall the current version of libfontconfig1, and intended to reinstall them from the downloaded packages.

The uninstalled packages were:

libfontconfig1, libfontconfig1-dbg,libfontconfig1-dev.

In the last parts of the uninstall, the computer froze, and I had to reboot. Upon rebooting, it said there was a file system mount error, and a maintenance terminal was started. Everything that was there previously seemed to be in place, so I did not want to reinstall the operating system, which would probably result in all of that being deleted. If there is a way to reinstall these packages via a utility shell, please let me know.

I believe this is the final variation on the door minder circuit. Because there wasn’t sufficient current from the encoder chip, we must drive the LED directly from the batteries, using a BJT, in this case, the 2N3904. The new LED, SFH4511, has a smaller half angle and higher radiant intensity than the TSAL6200, and better serves us at the distance we need to transmit the signal. Because we only need to see if the signal is interrupted, we will only transmit one bit, D0.

I am currently testing the circuit with the LED on top of the receiver, inside a black heat shrink tube in an orientation something like this:

The heat shrink tubing is needed because the receiver can still pick up infrared waves from the LED just being turned on. Another possible problem is that at distances of about 2 feet from the circuit, the receiver can pick up reflections off of skin and clothing.

An equivalent circuit to LED driver (driven from output of encoder chip) when on:

We use 0 for the resistor between ground and the emitter node. The power dissipation of the LED is 165mW, and the current through the LED is given by:

i_led=1.5v/R_led

Therefore, because P=vi, and we know the forward voltage drop for the LED is about 1.3v, R_led must be around 12 Ohms:

P=vi => 165mW=(1.3v)*(1.5/R_led) => R_led=1.95/0.165 Ohms = 11.8181 Ohms.

The base current can be calculated as (3v-1.5v+0.7v)/100Ohms=8mA. The emitter current is the current through R_led, 1.5/12=125mA. Adding these, the circuit uses 133mA when on.

The signal takes 27-28ms to be sent (see previous posts), so we should leave the encoder toggled for around 30ms, just to be safe. If we repeat this every 100ms, the encoder will be on 30% of the day. The batteries we use claim to provide 1500mA hours. Because 133mA is being used 30% of the time , we can use 30% of 133mA to calculate the circuit’s life. This is 1500mA*h/39.9mA=37.594h, about one and a half days.

We could turn on the LED every 200ms, and double the life to a little over three days (75.188h), but we will need to make sure the decoder receives every signal.

The new LEDs will arrive soon, it may be possible to get reliable results with less power, but previous experiments do not suggest this.

We set up this experiment according to the plan shown below. Someone wearing Pager 239 stood at all the places indicated by numbers 1-11. In the rigged trial, they stood in a manner that would collect the best data. In the natural trial, they moved around and tried to act natural. Lots of good data was collected. And here’s the report-

(more…)

I have attached a wiring diagram for the new pucks as reference. The orientation of the batteries is a top view of the puck with the USB pointed ‘up’. The triangle represents the circuit board with the switches, with the momentary switch at the bottom of the diagram and the two position switch at the top of the triangle. The green box represents the mote facing downwards (eg, as the mote will be mounted in the puck, with the buttons downwards)