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.

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 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.

RESULTS:

Position 1: (~)

In both the rigged and natural experiments, this position gave the expected results. Both experiments showed HandCleaner 103 at very high RSSI values.

The natural experiment actually worked better because it showed that Pager 239 and Anchor 51 were closer together.  Anchor 48 also responded, but at a lower RSSI. There was some action between 239 and Anchor 49.

The rigged experiment gave more signals from Anchor 48 and 49 and less from Anchor 51, so the rigged trial actually did not give us the perfect results we expected.

Position 2: (+)

The rigged experiment worked pretty well in this case. It showed low and high RSSI values between 239 and Anchor 48, showing entrance into the room. Many high RSSI values are seen, suggesting that the difference between in the room and out of the room was detected. Anchor 53 also received some messages from 239, which was acceptable because 53 was in the adjacent room.

The natural experiment again showed strong correspondence between Anchor 48 and 239. However, there was a lot of correspondence from Anchors 49, 51, 53, and 54. This suggests that with a person moving around in the room, more Anchors were able to pick up signals. Except for the correspondence with Anchor 54, the RSSI values decreased with distance, as expected.

Position 3: (++)

The results from both trials were clear. The high RSSI values indicated that 239 was very close to Anchor 58. The natural experiment gave the expected results with fewer and weaker signals from Anchors that were further away. (The rigged experiment did indicate a signal from HandCleaner 103, which is puzzling because it should not have been pushed.)

Position 4: (~)
[Wrong graph ?]
Since position 4 was between all the points, a lot of Anchors were expected to respond to it. 51 was expected to respond to it at higher strengths because both were outside of the room. In the rigged experiment Anchors 49, 51, 53, and 54 responded at that expected RSSI values (49 > 51 > 53(avg) = 54). HandCleaner 100 responded with very high RSSI values as expected.

In the natural experiment, all of the Anchors responded with approximately equal response, which could be expected with someone moving around. However, Anchor 51 should have higher RSSI values to indicate out of the room, and this was not the case. It seems as though the Hand Cleaner was not activated during the natural trial.

Position 5:  (~)

Position 5 was in the middle of the middle room. Higher RSSI values were expected from Anchors 53 and 54. In the rigged trial, this gave the expected results from Anchor 54, which was a lot higher than 53. Anchors 49 and 48 also gave responses, but at lower RSSI values, as expected.

In the natural trial, higher RSSI values from 54 were also seen. The pattern followed the expected pattern with 53 and 54 having higher RSSI values than the other positions.

Perhaps the placement of Anchor 53 had something to do with the lower RSSI values received (?).

Position 6: (-)

In position 6, there should have been very high RSSI values between Anchor 53 and 239. In the rigged trial, this was not seen (the highest was with Anchor 48). The natural trial also showed the same trend. Among the Anchors, Anchor 53 always received the strongest signal, but 239 received pretty strong signals from Anchor 48.

Position 7: (~)

In position 7, the highest RSSI values were always from correspondence between 239 and Anchor 54, as expected. In both the rigged and natural experiments, the messages received by the Anchors seemed to follow the pattern expected, with 54 being the strongest then 53, 49, 48, 51. However, the messages received by 239 do not follow this pattern. For example, in the rigged trial, RSSI for Anchor 48 was greater than that from 49, which was not expected.

Position 8: (+)

The rigged trial went very well. The highest RSSI values corresponded to HandCleaner 102 talking with 239. Also, the difference between in the room and out of the room was seen because Anchor 51 gave the strongest signal among Anchors.

The natural trial also gave some expected responses. The highest RSSI was between HandCleaner 102 and 239. The next highest was from Anchor 49 which was in the room, this could have been expected because with moving around, 239 could have communicated with Anchors 49, 51, and 54 pretty well. The results support this with higher RSSI values with 49, 51, and 54 than those with 48 and 53.

Position 9: (+)

Position 9 was barely in the room, so higher RSSI values with 49 were expected. The rigged trial went well, showing this, and some correspondence at very low RSSIs with 51 and 54. The natural trial also followed this trend, except for some correspondence with Anchor 48 (noise) and some correspondence with HandCleaner 102 (?).

Position 10: (++)

Position 10 was deep in the room. High RSSI values were expected between Anchor 49 and 239. In both trials, this was seen. In the rigged trial, lower RSSIs were seen from Anchor 54, which was understandable because 54 was in the adjacent room. In the rigged trial, some RSSIs from 54 were also seen. But, Anchors 49 and 53 also talked to 239, but at lower RSSIs, indicating distance. This was good because the RSSI values reported decreased and distance increased, which is what is expected.

Position 11: (~)

Position 11 was at the nurse’s station. A high RSSI value between 239 and Anchor 51 was expected. The rigged trial followed this perfectly, with some action at very low RSSIs from Anchor 54. However, the natural trial did not go as well. Lots of signals were picked up from the different anchors. Overall the highest were from Anchors 51 and 48. The data was not as defined as with the rigged trial, but with moving around it could be accounted for. We did expect 51 to be the highest, but this was not as clear in the natural trial.

Overall, I would say the experiment went pretty well. Most of the trials weren’t too far away from what we were expecting. Some of them had iffy results, but for the most part the data confirmed what we expected to see. Some things to work on are: reducing noise by maybe repositioning the anchors and making RSSI values more defined- so in the room and out of the room are clearer (which could happen with the new antennae).

Previously, the experiment was ran with both chips on the same board with both the LED and transceiverpointing towards a mirror. A signal was produced, but last night, I realized this was a reflection of of my shirt/hand. I believe the LED is not focused enough. The current through the LED in both cases was around 45mA (I didn’t have a chance to test it with anything lower before I broke the LED). I am, of course open to any ideas on how to proceed.

Practice In Lab
(1)Make sure Base Station picks up signals from all pieces
(2)Make sure everything syncs + shows up on the demo run as its supposed to
(3)Get all supplies in tool box
(4)Pack up all programmed motes

Set-Up In Hospital
(1)Unpack all parts
(2)Check that everything is still in working condition
1.Batteries still working
2.Hand cleaners properly calibrated
3.runsfb again and see that everything shows up
(3)Put all parts in their specific locations

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.

This seems like a good idea, but we must also account for a 27ms delay between when a pin on the encoder is toggled, and the corresponding changed is noticed on the decoder. Here is a screen from the oscilloscope:

The output from the pin on the decoder is on top, and the toggle for the encoder is on bottom. An oscillating toggle was used so we could view this delay on the scope. Notice the 27ms gap, shown by the cursors, between when the encoder is toggled again from being off, and the change in the decoder pin.

To be clear, a “broken signal” in Mike’s comment means there is no change in the output of the pin on the decoder. Notice on the scope, it only changes when the LED is on, goes off again, and then comes back on. If the second on, in this example is interrupted, and the LED goes off before the signal reaches the transceiver, the decoder pin will not change.

Here is a picture of the current circuit, as it is wired. For testing, I plan to put both on the same board.

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 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