Author Archives: mathscinotes

New Zealand Complex Phone Line Impedance

Posted on 15-June-2016 by mathscinotes

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 →

Posted in Electronics, Telephones | 1 Comment

Tank Track Ground Pressure Examples

Posted on 10-June-2016 by mathscinotes

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 →

Posted in Military History | 12 Comments

Instrumentation Amplifier Gain Adjustment

Posted on 9-June-2016 by mathscinotes

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 →

Posted in Electronics | Comments Off on Instrumentation Amplifier Gain Adjustment

Educating Children Is Expensive, But Ignorance Costs More

Posted on 8-June-2016 by mathscinotes

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 →

Posted in Humor, Personal | Comments Off on Educating Children Is Expensive, But Ignorance Costs More

A Lesson Learned from Lab Testing a Colpitts Oscillator

Posted on 7-June-2016 by mathscinotes

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 →

Posted in Cabin, Electronics | Comments Off on A Lesson Learned from Lab Testing a Colpitts Oscillator

Effect of Centrifugal Force on Weight

Posted on 6-June-2016 by mathscinotes

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 →

Posted in Physics | 7 Comments

Computing Lux Level Given A Lamp's Power Spectrum

Posted on 2-June-2016 by mathscinotes

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 →

Posted in optics | Comments Off on Computing Lux Level Given A Lamp's Power Spectrum

Backup Power For My Cabin

Posted on 1-June-2016 by mathscinotes

My wife and I are in the process of designing our northern Minnesota retirement cabin – the current structure is too primitive for any extended stay. Because power is unreliable in the north woods, I am researching whole-home battery backup options. One possible option is the Tesla Powerwall, which provides 6.5 kW-hr of energy per battery pack. You can increase capacity by adding battery packs as you need. Continue reading →

Posted in Batteries, Electronics | Comments Off on Backup Power For My Cabin

Quick Look at a Colpitts Oscillator

Posted on 26-May-2016 by mathscinotes

We have Memorial Day off from work and that can only mean one thing – time to work on some circuits for home projects. I have another inductive sensor project for which I want to generate a frequency that depends on the inductance value. The Colpitts oscillator is a good circuit for this type of application.

This is a quick note to document how I analyzed a circuit that I found on a tutorial and verified a statement made on the tutorial about the minimum gain required to startup the oscillation. I also derived an expression for the oscillation frequency. Continue reading →

Posted in Electronics | 5 Comments

Dynamical Parallax Examples

Posted on 25-May-2016 by mathscinotes

Years ago, I read the book Parallax (Figure 1) and really enjoyed the tale of how 19th century astronomers measured the distance to the nearest stars. This measurement was critical to providing scientists some idea as to the scale of the universe.

The book Parallax describes how simple trigonometry, along with the introduction of large telescopes coupled to precision measurement gear, could be used to measure the angular parallax of a star as the Earth revolved around the Sun – a method called trigonometric or stellar parallax. During my recent perusing of the Wikipedia, I discovered that there was an alternative form of parallax measurement, called dynamical parallax, that allows one to estimate the distance to stars that are beyond the limits of trigonometric parallax. Continue reading →

Posted in Astronomy | Comments Off on Dynamical Parallax Examples