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Author Archives: mathscinotes
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
One WW2 battle that we hear little about was fought by logisticians. Their battle was between what could be produced versus what could be delivered in time to matter. This point was driven home to me when I heard a WW2 historian say that the US had the manufacturing capacity to produce 150K tanks, but that level of tank production would consume all the US steel and leave nothing to build the ships needed to carry the tanks to the fight. Continue reading
I have been doing some metalwork lately that involves using units of "gauge". You will find the term gauge used in the measurement of wire, metal thickness, and pipe bore diameter. This quaint, but confusing, measurement system is slowly falling out of favor (example, sheet metal thickness gauge). Continue reading
I have now started on my next employment adventure. I can only say thanks to the wonderful team of people that I leave behind. They created the products that allowed the Fiber-To-The-Home (FTTTH) market to flourish. Tens of millions of FTTH products are now manufactured every year by companies around the world. These products are amazing in that for very low-cost they can contain such diverse technology: high-speed digital electronics, FPGAs, RF video, telephony, battery backup, and wireless. The team can be proud of what they have done. You succeeded where many others failed. Continue reading