EAST Knowledge

Saturday, September 5, 2015

Coffee Break #4

After taking a break over summer, EAST Knowledge is ramping up again with a coffee break. We invite you to join us for coffee at Cafe Delirium. If you haven't made it to one of our talks, the coffee breaks provide a nice opportunity to drop by and introduce yourself. We have the room in the back reserved. We're going to hang out for a couple of hours, so feel free to come by, talk shop, show off what you're working on, ask questions and pick each other's brains. We look forward to seeing you there! All are welcome!

What:	Coffee Break
Where:	Cafe Delirium
	308 N Main Ave, Gresham (map)
When:	10:00am - Noon, Saturday, September 19th, 2015
Why:	Sharing what we know over good coffee

Sunday, May 17, 2015

Coffee Break #3 - Recap

We held our third Coffee Break at the pleasant Cafe Delirium. We had enough people show up that we may have to consider a location that can accommodate more people for next time. We forgot to take pictures again, but I did try to do a better job of taking notes.

Pat brought his Arietta board to show us. He had attached a proximity detector on to the I²C bus. The proximity detector has a range of 5mm - 100mm. He is investigating incorporating the detector into his pick and place machine (previously discussed here and here).
Pat also mentioned a youtube video which gave what he felt was an elegant explanation for capacitors in series. (I'm still tracking down that video, so I'll try to update this page when I get a link.)
We briefly discussed the pros and cons between Xilinx and Altera FPGA development tools and their different soft CPU cores.
We also talked about a desire to learn more about Linux containers and web development frameworks. Charles is using some of these things in his work, and utilized containers in the IPython notebook demo he gave to the group.
Michael thought to bring with him several examples of items he had printed from his 3D printer. He has been finding many uses for it.
- He discussed some of the pros and cons of the designs that can be found on Thingiverse.
- He prefers to use Thingiverse for inspiration for creating his own designs as he has found he often cannot use the designs straight from the site.
- He mentioned that he has discovered the importance of the interaction of the slicer software and the printer control software, and he has learned a lot about the work flow for 3D printing.
- Michael pointed out that the company that produces his printer has just announced a smaller scale printer: Printrbot Play.
We also discussed vacuum tube audio amplifiers and restoring other older equipment. Bill has found he can often find many pieces of older test equipment that can be had cheaply and just needs a little effort to get working again.
- As we were discussing this, Chuck mentioned that at one time people actually installed phonographs into their cars. Something that most of us did not realize, and we were astounded that people would actually play their records while driving down the road. Virginia later dug up some internet evidence of these entertainment systems.

That's everything from my notes, and I know these are just the highlights. If I've left anything out you'd like me to include, please don't hesitate to mention it.

I think everybody had a good time. The coffee breaks make a great opportunity for pleasant, wide ranging conversations. Thank you to everybody who came out. And if you couldn't make it, we hope to see you next time!

Tuesday, May 5, 2015

Coffee Break #3

Update: A meeting recap.

EAST Knowledge is pleased to announce it's third "Coffee Break"!

We invite you to join us for coffee at Cafe Delirium. If you haven't made it to one of our talks, the coffee breaks provide a nice opportunity to drop by and introduce yourself. We have the room in the back reserved. We're going to hang out for a couple of hours, so feel free to come by, talk shop, show off what you're working on, ask questions and pick each other's brains. We look forward to seeing you there! All are welcome!

What:	Coffee Break
Where:	Cafe Delirium
	308 N Main Ave, Gresham (map)
When:	10:00am - Noon, Saturday, May 16th, 2015
Why:	Coffee and sharing what we know

Tuesday, April 21, 2015

Meeting #5 - Recap

"Locating Intrusions Using Fiber Optics"

For its fifth meeting, EAST Knowledge was pleased to have Jim Rulla as its guest speaker. Jim previously spoke at EAST Knowledge for our second meeting, and he was gracious enough to come back. The topic of this meeting was “Locating Intrusions Using Fiber Optics”. As usual, we’ll do our best to report on the talk, but these summaries are in no way intended as a substitute to seeing the talks in person.

Jim, always an engaging speaker, opened his talk by showing the audience a front page news story from 2012 about a man whose jet ski had broken down while riding it New York's Jamaica Bay. The man swam three miles to shore and climbed the fence at the JFK airport without detection. It was a dramatic example of the importance of perimeter security, and an example of where the technology Jim was about to talk about could be applied.

Basics of Interferometry

Jim gave a basic description of interferometry. Interferometry is a way to perform high precision measurements on the order of wavelengths of light. Interferometry relies on the wave properties of light. When multiple waves are combined, they add together. This adding together can be constructive (when both waves are positive), or destructive (when one wave is positive and the other negative). A basic interferometer uses a laser source, a beam splitter, two mirrors, and a detector. Example from wikipedia:

The key to the interferometer shown above is that the light travels along two different paths but are recombined in the detector. Now if you move one or both mirrors, the path length of the two light beams will change. This will cause fringes to appear at the detector as the two light beams will be slightly out of phase with one another. If you are varying the position of the mirrors in time, the fringe patterns will also vary in time. Example fringe patterns:

Colored and monochromatic fringes in a Michelson interferometer.

How Interferometry can be Used to Detect Intrusion

Jim had his custom software that he used to demonstrate the basic sort of signals that would be generated by a an interferometer. In the picture you see below, there are two large plots. The large plot on the bottom represents the position of one of the mirrors over time. The large plot on the top represents the signal that is detected where the two light beams come back together. As the mirror moves up and down (changing the path length the light travels), you can see the affect on the brightness of the light. Notice that when the mirror isn’t moving, the signal is flat (left side of plots).

Top plot represents interferometer signal. Bottom plot is the mirror position. Notice that when the mirror isn’t moving, the signal is flat (left side of plots).

To detect an intrusion using interferometry, you would need an interferometer where an intrusion would disturb the path length of light. You can create an interferometer using fiber optics. If you then run the fiber optics along a fence (for example), any disturbance on the fence will cause a disturbance in the fiber optics. This in turn changes the path length of the light, which will create interference patterns that are then detected. In the absence of an intrusion, you have a flat signal. Once an intrusion occurs, the signal begins to change rapidly. Detecting when the signal is changing is all that is needed to detect the intrusion.

Jim also mentioned that basic interferometry makes it difficult to determine which direction the path length has changed. You’ll notice in the plot shown above that as the mirror changes direction, the output of the basic interferometer continues to change in the same way. However, modulating the light being used from the interferometer provides phase information. One possible way of doing that is by vibrating one of the mirrors. This technique is known as "homodyne modulation".

How Interferometry can be Used to Detect Location

Now that we have a basic interferometer detection, how can that be used to detect location? Jim showed a diagram (poorly) captured in the photo below. In the top, you see two fiber optic interferometers (one black the other red). These interferometers run in opposite directions in the same bundle of fiber. Because the interferometers are in the same bundle, what happens to one interferometer also happens to the other. If an intruder is climbing a fence, he will disturb both interferometers.

Because the interferometers are running in opposite directions, the signal produced by one interferometer is displaced in time relative to the other interferometer (see the red and black step plot in the picture below). This time difference varies depending on where the intrusion occurs. If you can calculate the time difference, then you can determine the location of the intrusion because you know the speed of light. Pretty cool!

In order to determine the time difference you have to perform a correlation on the two signals. The correlation isn’t perfect and can be computationally expensive, but using the correlation, you can get an estimate of the time difference between the intrusion signals.

The two interferometers running in opposite direction are shown on top. In the middle you see a simple plot showing the interferometer signals from a single intrusion. Notice that the intrusion signals are offset in time.

Jim showed that with this method of determining location that there is a direct relationship between the speed of light and how rapidly you would have to sample the signals. For example, to try to get an accuracy of +/- 25 m, you have to sample the interferometer at least 10 MHz. He further emphasized that if you have a typical DSP running at 500 MHz, that you would only get 50 clock cycles per sample. That means that to properly process the incoming data, you need to have the appropriate model and the appropriate, efficient approach. Using his software, Jim showed off several different approaches to processing the signals. In one example he emphasized the processing speed. In another he emphasized the accuracy and certainty of the location calculation. He suggest that for this particular application it is possible to get both.

Afterwards

Both during and after the talk, the audience had a lot of great questions and made several astute observations. We also have some leads on possible future talks. For anybody who might be interested in discussing some tech topics that interest them, get in touch. You’ll find a receptive audience with EAST Knowledge. If you’re eager to share, we’re eager to learn.

We hope to see you next time for stimulating conversation. (We also have coffee, cookies, and Raspberry Pi.)