Day: February 7, 2022

Is Your Flashlight A Lumen Liar? Build A DIY Integrating Sphere

February 7, 2022 by 3 Comments

A lamp used to be simple thing: just stick a filament in a glass bulb, pass a current through it and behold! Let there be light. A bigger lamp meant a larger filament, taking more power and a larger envelope. Now we’ve moved on a bit, and it’s all about LEDs. There really isn’t such a thing as ‘just an LED,’ these are semiconductor devices, made from relatively exotic materials (OK, not just plain old silicon anyway) and there is quite a lot of variety to choose from, and a bit of complexity in selecting them.

For [Torque Test Channel] the efficiency of conversion from electrical power to radiant power (or flux) is the headline figure of interest, which prompted them to buy a bunch of lamps to compare. To do the job justice that requires what’s known in the business as an integrating sphere (aka an Ulbricht sphere), but being a specialist device, it’s a bit pricey for the home gamer. So naturally, they decided to build the thing themselves.

Coating the inside of the foam sphere took several attempts.

Firstly they did the sensible thing, and shipped off their test units to a metrology lab with the ‘proper’ equipment, to get a baseline to calibrate against. Next they set about using some fairly common materials to construct their sphere. The basic idea is quite simple; it has a uniform diffuse internal surface, which ensures that all photons emitted by a source can be measured at the appropriate measurement port, regardless of the angle they are emitted from the source. This way, the total radiated power can be determined, or at least estimated, since there will be a degree of absorption.

Anyway, after a couple of false starts with coating the internal surface, they came to the conclusion that mixing barium sulphate into the paint, and then a bit of a rub-down with sandpaper, gave the required pure white, diffuse surface.

The results from their testing, using a lux meter inserted into one of the other ports, showed a pretty good correspondence between their measured lux figure and the lab-determined lumens figure. Since one lux is defined as one lumen per square meter, they seemed to get lucky and found a consistent ten-to-one ratio between their observed value and the lab. This factor will be simply due to the physical setup of their contraption, but an encouraging result so far anyway. And what about the bottom line? Did those test units deliver their promised lumen output? It would seem that they pretty much did.

When it rains, it pours. Just a few hours ago we saw another DIY approach to building an integrating sphere, this time using a small cannonball mold of all things. Before that we hadn’t actually seen too many light measurement projects, save this old one that used the chipKIT. Continue reading “Is Your Flashlight A Lumen Liar? Build A DIY Integrating Sphere” →

Remembering The MIT Radiation Laboratory

February 7, 2022 by 31 Comments

Back in the late 80s, our company managed to procure the complete 28 volume MIT Radiation Laboratory (Rad Lab) series, published in 1947, for the company library. To me, these books were interesting because I like history and old technology, but I didn’t understand why everyone was so excited about the acquisition. Only a cursory glimpse at the volumes would reveal that the “circuits” these books described used vacuum tubes and their “computers” were made from mechanical linkages. This was the 1980s, and we worked with modern radar and communications systems using semiconductors, integrated circuits, and digital computers. How could these old musty books possibly be of any practical use? To my surprise, it turned out that indeed they could, and eventually I came to appreciate the excitement. I even used several of them myself over the years.

Radiation Lab? Nuclear Radar?

In the years leading up to WW2, the idea of a civilian organization of scientists that would operate independently of the military and government bureaucracies was being championed by Dr. Vannevar Bush. The military and scientists had not worked well together during the first World War, and it looked like science and technology would be playing a much bigger role in the future.

It seemed certain that America would enter the conflict eventually, and Dr Bush and others believed that a new organizational framework was called for. To that end, the National Defense Research Committee (NDRC), which later became the Office of Scientific Research and Development (OSRD) was pitched to President Roosevelt and he approved it in June of 1940.

Almost immediately, a gift fell in the lap of the new organization — the Tizard Mission which arrived in the states from the UK in Sep 1940. They brought a literal treasure chest of technical innovations from the British, who hoped that US industry’s cooperation could help them survive what looked like certain and imminent invasion. One of those treasures was the cavity magnetron, which our own Dan Maloney wrote about a few years ago.

Within a few weeks, under the guidance of young Welshman “Taffy” Bowen, they had reviewed the design and gathered up the necessary equipment to fire it up. A 10 kV anode power supply and a 1,500 gauss electromagnet were procured, and the scientists gathered at the Bell Radio Laboratories in Whippany New Jersey on Sunday, Oct. 6, 1940. They powered up the cavity magnetron and were blown away by the results — over 10 kW of RF at 3 GHz (10 cm) from something the size of a bar of soap. Continue reading “Remembering The MIT Radiation Laboratory” →

“Lazier” Web Scraping Is Better Web Scraping

February 7, 2022 by 13 Comments

Ever needed to get data from a web page? Parsing the content for data is called web scraping, and [Doug Guthrie] has a few tips for making the process of digging data out of a web page simpler and more efficient, complete with code examples in Python. He uses getting data from Yahoo Finance as an example, because it’s apparently a pretty common use case judging by how often questions about it pop up on Stack Overflow. The general concepts are pretty widely applicable, however.

[Doug] shows that while parsing a web page for a specific piece of data (for example, a stock price) is not difficult, there are sometimes easier and faster ways to go about it. In the case of Yahoo Finance, the web page most of us look at isn’t really the actual source of the data being displayed, it’s just a front end.

One way to more efficiently scrape data is to get to the data’s source. In the case of Yahoo Finance, the data displayed on a web page comes from a JavaScript variable that is perfectly accessible to the end user, and much easier to parse and work with. Another way is to go one level lower, and retrieve JSON-formatted data from the same place that the front-end web page does; ignoring the front end altogether and essentially treating it as an unofficial API. Either way is not only easier than parsing the end result, but faster and more reliable, to boot.

How does one find these resources? [Doug] gives some great tips on how exactly to do so, including how to use a web browser’s developer tools to ferret out XHR requests. These methods won’t work for everything, but they are definitely worth looking into to see if they are an option. Another resource to keep in mind is woob (web outside of browsers), which has an impressive list of back ends available for reading and interacting with web content. So if you need data for your program, but it’s on a web page? Don’t let that stop you!

As Light As Plastic; As Strong As Steel

February 7, 2022 by 38 Comments

Chemical engineers at MIT have pulled off something that was once thought impossible. By polymerizing material in two different directions at once, they have created a polymer that is very strong. You can read a pre-print version of the paper over on Arxiv.

Polymers owe many of their useful properties to the fact that they make long chains. Molecules known as monomers join together in strings held together by covalent bonds. Polymer chains may be cross-linked which changes its properties, but it has long been thought that material that had chains going through the X and Y axis would have desirable properties, but making these reliably is a challenge.

Part of the problem is that it is hard to line up molecules, even large monomers. If one monomer in the chain rotates a bit, it will create a defect in the 2D structure and that defect will grow rapidly as you add more monomers. The new technique is relatively easy to do and is irreversible which is good because reversible chains tend to have undesirable characteristics like low chemical stability. Synthesis does require a few chemicals like melamine, calcium chloride, pyridine, and trimesic acid. Along with N-Methyl-2-pyrrolidone, the mixture eventually forms a gel. The team took pieces of gel and soaked it in ethanol. With some filtering, ultrasonics, centrifuging, and washing with water and acetone, the material was ready for vacuum drying and was made into a powder.

The powder is dissolved in acid and placed on a spinning silicon wafer to form a polymerized nanofilm. Other 2D films have been produced, of course, such as graphene, but polymer films may have a number of applications. In particular, in contrast to conventional polymers, sheets of this material are impermeable to gas and liquid, which could make it very useful as a coating.

According to the MIT press release, the film’s elastic modulus is about four and six times greater than that of bulletproof glass. The amount of force required to break the material is about twice that of steel. It doesn’t sound like this material will be oozing out of our 3D printers anytime soon. But maybe one day you’ll be able to get 2D super-strong resin.

For all their faults, conventional polymers changed the world as we know it. Some polymers occur naturally, and some use natural ingredients, too.