Author Archives: mathscinotes

How Much Does A Cloud Weigh?

Posted on 12-August-2011 by mathscinotes

Introduction We have had a lot of rain in Minnesota this summer. As I sit here staring at the rain falling hard outside, I occurs to me that a cloud must be a very heavy thing in order to drop … Continue reading →

Posted in General Science | 6 Comments

More Interview Criteria and A Funny Story

Posted on 3-August-2011 by mathscinotes

I read a management forum on LinkedIn that I like. The following exchange was on the forum yesterday that made me smile. Two people were discussing how to evaluate an interviewee. Justin Hoffman • I use four simple guidelines (KSQB) … Continue reading →

Posted in Management | 1 Comment

Capacitor Puzzle Redeux

Posted on 25-July-2011 by mathscinotes

My first blog post discussed the following interview question I received many years ago. You are handed a 1 F capacitor charged to 10 V and two boxes containing uncharged capacitors: one box contains an uncharged 1 F capacitor and … Continue reading →

Posted in Electronics | 4 Comments

Thermistor Mathematics

Posted on 22-July-2011 by mathscinotes

A common electrical engineering task during the design of a circuit card is designing a way for the circuit to measure its own temperature. Knowing the temperature of a circuit board is important for compensating for component temperature variations and diagnosing heat problems. Normally, I use a thermistor as my temperature probe. A thermistor is a resistor whose resistance varies with temperature (Figure 1). The thermistors that I use have a negative temperature coefficient (NTC), which means their resistance reduces as their temperature increases. In many ways, thermistors are a great sensor: cheap, tough, small, and accurate. Continue reading →

Posted in Electronics | 35 Comments

Speed of a Meteor

Posted on 8-July-2011 by mathscinotes

I own a small cabin on a lake in Northern Minnesota. Years ago I showed my brother how to find satellites, planets, and meteors. I love to lay on the dock at night and watch the sky. Because Northern Minnesota is so sparsely populated, the sky is incredibly dark and the stars are so much brighter than in the metropolitan region where I spend most of my time. When people visit me at the cabin, I take them out on the dock and introduce them to the world of meteors, satellites, and planets. It is always a good time. Continue reading →

Posted in Astronomy | 28 Comments

How to Interview Engineers

Posted on 29-June-2011 by mathscinotes

My youngest son has a long drive to and from work everyday. During his drive home, he frequently calls me to help him pass the time. During a recent drive, we talked about how I interview engineers, which I have done hundreds of times. I have a fairly standard interview methodology. The key part of any interview is how you go about grading the applicants. Continue reading →

Posted in Management | 1 Comment

Another Analog Design Legend Dies

Posted on 20-June-2011 by mathscinotes

I just saw the announcement that Bob Pease died in a car accident after leaving a memorial to Jim Williams, another analog legend. This is very sad. I have read everything that Bob Pease wrote. His column for Electronic Design, "Pease Porridge," was required reading for my crowd. Continue reading →

Posted in Electronics | Comments Off on Another Analog Design Legend Dies

Density of a Neutron Star

Posted on 19-June-2011 by mathscinotes

Television science programs frequently talk about black holes and neutron stars. A common quote during these programs is something like "a teaspoon of neutron star stuff weighs a billion tons" or some other similar statement. I always find numbers like these interesting to look at in detail. Continue reading →

Posted in Astronomy | Comments Off on Density of a Neutron Star

The Papoulis Filter (aka Optimum "L" Filter)

Posted on 17-June-2011 by mathscinotes

Analog engineers often have to design filters, which generally entails a lot of polynomial manipulation. Since I am currently designing some active filters, I thought it would be worthwhile documenting a filter function that I am using right now, but that is not widely known. This is the Papoulis or Optimum "L" filter. For this article, I will refer to this filter as the "L-filter." The "L" stands for Legendre, a mathematician whose like named polynomials are used in the derivation of the function. Continue reading →

Posted in Electronics | 13 Comments

The Passing of an Analog Electronics Giant

Posted on 14-June-2011 by mathscinotes

I just saw the announcement that Jim Williams passed away. This guy was an inspiration to me. His apps work at National Semiconductor was a model for the industry. His articles in magazines like EDN provided real-world examples of elegant analog design techniques. His books, particularly Analog Circuit Design: Art, Science and Personalities, provided wonderful examples of problem solving. He will be missed. Continue reading →

Posted in Electronics | Comments Off on The Passing of an Analog Electronics Giant