Comments for Hand Hygiene

Comment on Testing RSSI Values at Different Locations by tedherman

tedherman — Sat, 06 Mar 2010 21:32:37 +0000

There could be variations of this type of result over different pagers, of course. One thing I’d like to point out is that you are using a much higher density of anchors and handcleaners than what we had originally designed for. If it works, good. But there will possibly be some problems with the wireless (due to message collision) at this density.

Comment on Possible IR Encoder/Decoder for door minder by michaelireland

michaelireland — Fri, 26 Feb 2010 19:46:45 +0000

It may be useful, instead of oscillating the input to the encoder, to have the mote toggle the input to the encoder. This should cause a code to be sent once and received, which will then cause the corresponding pin on the decoder to toggle. The mote can then verify this toggle to indicate that the beam is uninterrupted. The mote can run this routine every 5ms or so. Two or three failed transmissions in a row could be considered as an activation, and the mote could then broadcast it’s “my beams been broken” signal.

Comment on Some notes on force sensitive resistors by michaelireland

michaelireland — Fri, 26 Feb 2010 19:37:52 +0000

If the design has a constant area of contact with the sensor, than the area factors out and the sensor is in effect force dependent. The size of the area of contact you choose determines the range of forces the sensor can respond to correctly.

Comment on Battery Test 2 by gthomas

gthomas — Wed, 24 Feb 2010 16:30:21 +0000

Great work, Greg. I’m glad you checked on the batteries the next day to see what happened to them. It may be that they don’t completely turn off, just that they turn off most of their functions. I would have thought that their power drain was so slow that they wouldn’t be at zero the next day, however. Perhaps we should shut them off a little earlier, before they get into the steep descent part of their curve. As for the difference between the 3.2v and 2.5v readings, I wonder if the battery voltage drops when sourcing a current when the battery is mostly depleted.

Comment on Puck Reliablility Results from 2/14/10 Tests by gthomas

gthomas — Sun, 21 Feb 2010 15:43:34 +0000

I tried to line up the hits for the foam trial and got only 11 misses. There were a number of presses that happened after the fact. Also, I’m suspicious that the start times of the paper recording and the mote recordings don’t line up. Can you please post what you recorded on paper so we can see the details? It would be nice to have a little more explanation about how you found the start and end of the data sets, because we may have an issue there.

Comment on Some notes on force sensitive resistors (cont’d) by gthomas

gthomas — Fri, 19 Feb 2010 15:51:24 +0000

The way I interpreted the passage is that the position of the book on the acrylic block would be expected to change the reading, possibly because if the book was balanced on the block towards so that it’s center of mass was towards the top of the block, then the top row of cells would receive more pressure than the bottom row. Apparently this would give a different result than if the book was exactly centered or shifted slightly downward. At least that was my interpretation. Clearly it is saying that you can’t expect a deadweight test to give repeatable results.

Comment on Our First Puck Experiment by gthomas

gthomas — Fri, 19 Feb 2010 15:42:07 +0000

Great start. However, I think that Phil and I were looking for a slightly different analysis. I think the statistics you present measures the interarrival time of the pucks as a function of the interarrival time recoded by the experimenters. My guess is that the R^2 value is largely dependent on the accuracy of the experimenters — the differences between when the mote was actually pressed and the time the experimenters recorded by hand. What we are most interested in are false alarms and misses. To find this you need to set up a 2×2 grid for each experiment. The two columns should be labeled “Dispenser Pressed” and “Dispenser Not Pressed”. The two rows should be labeled “Puck Activated” and “Puck Not Activated”. Divide the time sequence into periods during which the protocol indicates a period during which the puck should have been activated (perhaps a 5 second period) and a period when it should not have been activated (perhaps a 15 second period). In experiment 1 we had 40 puck activations and 39 periods during which there was no puck activations. Go through the puck activation record and check for each interval whether or not there was a puck activation. If the puck was completely reliable, it should have 40 activations when we predicted activations and 39 intervals in which there were no activations. There should also be zero periods when we predicated and activation but saw none and no periods when we expected no activation but saw one anyway.

We should end up with a 2×2 matrix for each experiment.

Comment on Battery Test Results by gthomas

gthomas — Fri, 19 Feb 2010 15:12:31 +0000

I’m sick today and not firing on all cylinders. Gregg and I reread your post and are having trouble understanding what you are suggesting. Here’s how I interpreted it:

The old code reads substantially higher ADC values than the new code. We could set up the ADC link with the new code and if we don’t get a reasonable reading (e.g., something between 1600 and 2600), we could that the mote is one of the old ones without a proper voltage divider. In that case, we could run the old ADC code and see if we got some value between 2600 and 4000, indicating a valid internal voltage. We could then monitor the internal voltage to shut the old-style pager off before it runs out power.

I’m pretty sure that I don’t have your idea quite right, but hopefully I’m close.

However, we think that the old code wouldn’t work very well without the voltage divider. When we tested the pagers initially, we discovered that the voltage values were out of range — we thought they were on a 5V scale and they were really on a 2.5V scale. We changed the resister values in the voltage divider and got ADC readings that were in range. Therefore the resister values affect the reading that you’re calling the internal voltage. This result gives me a queezy, cognitive dissonance feeling. I haven’t be able to grasp why something called internal voltage should depend on a wire connected to an external voltage. I have a vague idea that is might have to do with a relative measurement on a mote that is designed to survive with a wide range of external voltage sources, but I’m really not sure.

Just to confirm that we’re not missing something important, Gregg is going to run a test looking for the ADC0 levels on a mote without a voltage divider or anything connected to the ADC0 pin. We’re thinking that he will just see noise.

Comment on Some notes on force sensitive resistors (cont’d) by tdecker

tdecker — Fri, 19 Feb 2010 05:10:20 +0000

I must not be understanding this passage. Does distribution refer to the actual physical location of the weight distribution over the area of the FSR? In that case, 5psi in the top right corner will not give the same resistance as 5psi in the bottom right corner, test to test. Or does it mean that a five separate 1psi areas will not give the same resistance as one 5 psi area? Or both of these things?

In my case, I would think that there would be little variation of the weight distribution between tests: I placed the acrylic block on the FSR, added a 500g weight, removed the weight leaving the block in the same location, and added the next weight, and so on. Undoubtedly the block shifted while I lifted/placed the weights, but I would think it would be a negligible amount. (Or does that passage say that even a negligible amount would have a disproportionate effect on the output?)

Comment on Some notes on force sensitive resistors (cont’d) by gthomas

gthomas — Fri, 19 Feb 2010 04:27:25 +0000

From page 8 of the integration guide:

Provide a consistent force distribution. FSR response is very sensitive to the distribution of the applied force. In general, this precludes the use of dead weights for characterization since exact duplication of the weight distribution is rarely repeatable cycle-to-cycle. A consistent weight (force) distribution is more difficult to achieve than merely obtaining a consistent total applied weight
(force). As long as the distribution is the same cycle-to-cycle, then repeatability will be maintained. The use of a thin elastomer between the applied force and the FSR can help absorb error from inconsistent force distributions.

I’m not sure your quick test is completely valid.