Monthly Archives: June 2016

3D Plot Example Using PCB Trace Current vs Trace Area and Temperature Rise

I was asked this morning about how to create a 3D plot in Mathcad that shows a surface, two lines on the surface, and marks the point of intersection of the two lines (Figure 1). It just so happens that I have been looking at the amount of current that a PCB trace of a given area can carry for a given temperature rise above ambient. While the curve itself is a bit boring and viewing it in 3D does not add any value, this example does illustrate the procedure for generating this type of plot. Continue reading

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A Little Analysis of a Visible Exoplanet

I saw an article in the popular science press about a real rarity – an exoplanet that can be seen (Figure 1). I dug around the web and found the journal article on which most of the press articles were based. Given their measurement data, I wanted to see if I could duplicate some of their computed exoplanet characteristics. In this post, I will be using some of the techniques learned about while listening to The Search for Exoplanets: What Astronomers Know. Continue reading

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Extended Reach PoE Example

The popularity of Power Over Ethernet (PoE) has proven that customers find value in using a single cable for both data and power distribution. Unfortunately, copper-based Cat 5e/6 cable is limited to a 100 meters because of data transmission issues. To circumvent this limit, some equipment vendors are using composite fiber/copper cables – a single cable that contains fiber for data and large gauge copper wire for power distribution (Figure 1). Continue reading

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New Zealand Complex Phone Line Impedance

I received an email today asking me about the phone line impedance differences between New Zealand (Figure 1) and Australia. This is an easy question to answer, and I wrote up a quick Mathcad worksheet to perform the calculation. Continue reading

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Tank Track Ground Pressure Examples

I have been reading some military history on tank operations during the WW2 and the subject of the ground pressure exerted by the tank's tracks has figured prominently in the discussions on the Eastern Front. The T34/85 was mentioned as a particularly mobile tank because of its low ground pressure. Since I am working diligently on improving my web scraping skills, I decided to generate a short table of the ground pressures of some famous tanks. Continue reading

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Instrumentation Amplifier Gain Adjustment

I have an existing circuit for which I need to modify the front-end gain. The gain is provided by an LT1101, which is a common instrumentation amplifier. This part is normally used with one of its two fixed gain settings (10x, 100x). As commonly happens, I need to find a way to resolve an issue without making major changes to a circuit. The designers of the LT1101 provided you a way to modify the amplifiers gain by adding two resistors to the circuit. Figure 1 shows the modified circuit, with the added resistors marked with red ovals and labeled Rx. Continue reading

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Educating Children Is Expensive, But Ignorance Costs More

Paying school bills is certainly not the only expensive item for parents. I often tell people that the most expensive movie I ever took my sons to was The Mighty Ducks – it cost me about $5k per year for a number of years. This was roughly the cost back in the 1990s of having two kids in traveling hockey. After my sons saw that movie, they were determined to become hockey players. Continue reading

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A Lesson Learned from Lab Testing a Colpitts Oscillator

It is the weekend and time to build my personal circuits. Some of my recent personal work has been focused on detecting cars in my cabin's driveway by using a loop of wire that experience an inductance change when a car passes over it. This weekend I built the Colpitts oscillator I discussed in this post, which is part of a car detector improvement I am considering. The circuit I am using now is not as sensitive as I would like, and I am hoping a few changes will allow me to detect smaller vehicles, like ATVs. Continue reading

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Effect of Centrifugal Force on Weight

I love to read Quora, and I often see interesting factoids there that I inspire me to put pencil to paper and verify them. This week, I read a response to the question "What does the pilot of a supersonic fighter feel when flying at Mach 3 at 40,000 feet?" I found one of the answers particularly interesting because of how the respondent generalized the question to make it more interesting. I love when people take a basic question and turn it into a more interesting question. Continue reading

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Computing Lux Level Given A Lamp's Power Spectrum

I have assigned my interns a couple of simple design tasks – one of the tasks involves performing measurements on that amount ambient light that leaks into our enclosures. This task is going to provide data that will drive the design of a simple ambient light sensor for use within our enclosures to tell if the door has been opened. Open door sensors are a notorious source of false alarms. We used to use mechanical/magnetic sensors, but they proved to be unreliable. We are now looking at using ambient light sensors. Continue reading

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