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Author Archives: mathscinotes
I have been working on improving my web scraping abilities by analyzing WW2 data. I have focused on topics related to how the US took the 14th largest military in the world and in roughly 18 months turned it into a military that could fight anywhere in the world. In this post, I want to look in detail at how war materials were delivered to beaches around the world using a vessel called a Landing Ship Tank (LST). I have wanted to write about the LST for a while, but the web data was distributed on about 1200 separate pages – one for each ship. While a Python script would have worked nicely, I wanted to try gathering the data without doing any programming. I found some software that did a good job automating this task, which I will discuss later in this post. Continue reading
It has been 50 years since 1968, and I have been seeing quite a few retrospectives on television about that tumultuous year. I was in 6th-grade in 1968 and the chaos of that year is still very clear in my memory – I remember spending quite a bit of class time on the Paris peace talks. One lesson was about how the Paris Peace negotiators argued about the shape of the table at which they would sit. Arguing about the shape of a table while people were dying seemed ridiculous to a 12-year boy. After hearing all these recent discussions about 1968, I decided to look at the US Vietnam casualty data (Figure 1) to see what insights I could gain on that year. All my work is done in Excel and my workbook is here. Continue reading
I almost sent out a spreadsheet today that contained a VLOOKUP error – I forgot that VLOOKUP is not case sensitive. Fortunately, I caught my error seconds before I hit send. Today's post is about how I chose to perform a case-sensitive lookup in an ancient version of Excel. Continue reading
I am doing some testing at an Electromagnetic Compatibility (EMC) facility this week. Part of the test specification requires that we inject audio frequency interference on the power supply lines at discrete frequencies that range from 10Hz to 100+KHz, with 30 frequencies selected from each decade of frequencies (e.g. 10 Hz to 100 Hz, 100 Hz to 1 kHz, etc.). Figure 1 shows a specification similar to the one I am performing. My test facility that has chosen the discrete frequencies to be evenly spaced on a logarithmic axis. I started to wonder how the frequencies were selected – let's work through it. Continue reading
I am currently working as a project manager on a serial data channel qualification task. During this work, I need to estimate the time required to perform dozens of Bit Error Rate (BER) measurements under different scenarios (see Figure 1). In these measurements, we are working to ensure that our BER is always 1E-10 or less. I have performed this calculation many times and have derived all the associated formulas here. BER is a statistical parameter and its measurement is a function of the confidence level you want in your answer. In this case, we want the highest confidence level possible consistent with a two-week test effort. Continue reading
I recently was asked if it was possible to design a circuit that will isolate a battery from a circuit until a momentary switch is closed (Figure 1). Once the momentary switch is closed, the battery is connected to the rest of the circuit and it cannot be disconnected by further mechanical switch closures. This was just a proof-of-feasibility exercise and NOT a final implementation. However, it was a good example of how to use LTSpice to verify the first design concept and is worthwhile documenting here. Continue reading
My wedding anniversary (16-June) and Fathers Day are on the same weekend this year. Next year, Fathers Day and my anniversary are on the same day. I became curious about (a) how to compute the date of Fathers Day for each year, and (b) determining the years when Fathers Day and my anniversary occur on the same date. Continue reading
I was reading an article about HVAC (Heating, Ventilation, and Air Conditioning) calculations in the Journal of Light Construction that had a quote I found interesting. It said that
… 17 extra occupants added more than a half ton of cooling load. Continue reading
I am working on a product that uses a Bosch BMA253 accelerometer as a motion sensor. This family of products has become a defacto standard for inexpensive motion detection. In this post, I will provide a simple power calculation example along with some empirical data that Bosch provided me. Normally, I would not consider a simple power calculation worth writing about, but the datasheet did not provide a worked example. I also provide an Excel workbook that parameterizes the critical variables. Continue reading
My first engineering manager was named Marl Godfrey. He was an excellent manager who also had keen insights into the human condition. These insights made quite an impression on my 22-year old self – I actually kept a notebook of his comments. Some of his most insightful comments were about the US military and the Vietnam War. Marl has grown up in Oklahoma and he had served in Vietnam. He once commented that Oklahoma had very aggressive draft boards, which resulted in Oklahoma having a relatively high death rate during the conflict. I was reminded of this statement when I recently reviewed my quote database. I thought that I should be able to determine how death rates varied by state during the Vietnam War, which is the subject of this post. Continue reading