Monthly Archives: June 2018

Switch-Controlled Circuit To Isolate Battery from Load

Posted on 19-June-2018 by mathscinotes

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 →

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Computing Dates of Fathers Day with Excel

Posted on 17-June-2018 by mathscinotes

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 →

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Air Conditioning Load of a Group of People

Posted on 12-June-2018 by mathscinotes

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 →

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Accelerometer Power Calculation Example

Posted on 8-June-2018 by mathscinotes

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 →

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State Casualty Rates During the Vietnam War

Posted on 5-June-2018 by mathscinotes

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 →

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