Gas station without pumps

2017 June 17

Kind thoughts from a student

Filed under: Circuits course — gasstationwithoutpumps @ 23:36
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One of my students sent me a nice e-mail at the end of the quarter.  With her permission I’m reprinting it here:

Dear Prof. Karplus,
I just wanted to take a moment to thank you and tell you how much I enjoyed the class over the last two quarters. Even though my scores may not reflect it, I feel like I’ve gotten the opportunity to learn a lot. In addition to that, some of the projects gave me a chance to spend time and connect with my father, who’s also an engineer. He was amazed at my ability to draw and build a circuit on my own (as I did the class-D lab solo), because he claims he was never able to do so when he first started learning electronics. The last project was especially very meaningful, since EKGs are  personal to me due to some childhood problems, and I got to learn how they work. I created my graduation cap as a tribute to that project and the class (see attached picture), I hope you like it!

Hope to see you at graduation,
Manisha

Manisha Marisetty’s graduation cap

A number of students in the class have told me how much they learned in the class, and not just about electronics. Other things students have mentioned include writing improvement, breaking things into subproblems, and debugging. This feedback from the students is valuable, as it keeps me motivated to keep improving the course. The course is a lot of work (for me and for the students), and it would be very easy to burn out if the course were not having much positive effect on the students.

Note: constructive criticism from the students is also useful—I’ve had several tell me that there need to be more drill exercises, for example, and there have been requests for more worked examples.  But small amounts of positive feedback help keep me motivated to do the work of addressing the problems. (Students have also suggested that I need to give more positive feedback—something I’m working on, but finding difficult to do consistently.)

I’m afraid I won’t go to the graduation ceremonies this year—I’ve got too much grading still to do, and I figure I’ll barely be completing the grading by the Tuesday deadline as it is. I’ve gotten the electrode-lab redone reports graded, and one third of the EKG labs done. I have the remaining 23 EKG lab reports to grade, an independent study, and a senior thesis. I’m on schedule, but not with a lot of time to spare.

2011 February 9

Thanks, Dad

My Dad turns 85 today, so I thought this would be a good time to thank him for all the things he did for me.  I’m not talking of the routine things, like keeping us fed, housed, and educated, but the special things that made him unique.

One particular thing I’d like to thank him for  is for introducing me to science and engineering as a child.  Most people have the impression that kids learn math and science in the schools, and that improving schools is key to creating more scientists and engineers. Personally, I have some doubts about this—I think that for decades US schools have done little to train future scientists and engineers, and that our country has been relying on an apprenticeship system, in which scientists and engineers train their children, at least until they go off to college. That is largely how it worked for me and for many of my colleagues.

I learned about logarithms and complex numbers from my dad, long before I saw the subjects in school. I learned how to use a slide rule, and why it worked (he also bought me my first calculator, back when that was an investment comparable to getting a top-of-the-line laptop today). I learned Ohm’s Law and about impedances and Wheatstone bridges from him—I never had a formal circuits course in college, though I ended up teaching VLSI design as a EE professor for 4 years and as a computer engineering professor for another 14 years.

I remember one joke Dad was fond of, which only works in German.  One goes through a the names of a number of cities (X) and asks where one can find the X Brücke, the answer being “in X”, ending up with the Wien Brücke, which is an electrical bridge with RC elements on two of legs of the bridge, not a bridge in Vienna.  The circuit has a strong frequency dependence, and a variant of it (the Wien-Robinson-Brücke) is the core of the Wien bridge oscillator that was Hewlett-Packard’s first product. (Although I learned German in high school, my Dad was helpful in keeping me interested in it and in improving my accent.  I have since forgotten a lot of grammar and the genders of many of the nouns, but I don’t have much of an American accent.)

My dad also provided us with lots of science toys, often in the form of kits or surplus equipment.  I particularly remember building and playing with Heathkits: a vacuum-tube voltmeter, a grid-dip meter, and (the biggest project) an oscilloscope.  I recently did some image searches on the web to try to identify the model of oscilloscope we had. As best I can tell, it was an OM-2:

I have recently bought myself a used oscilloscope and signal generator on ebay, for not much more than the original Heathkit cost, but this is a Kikusui COS-5060 60MHz, dual trace scope with fancy triggering options, not a bare bones 2MHz scope.  Even analog electronics have gotten cheaper over the years, not just digital. I plan to teach my son how to use these instruments, and hope he gets as much out of it as I got out of the Heathkit.  Probably not, though, since he won’t be building it, and it doesn’t come with detailed explanations of how it works.

Kikusui COS-5060 oscilloscope and Clarke-Hess model 744 function generator, bought on e-bay for $102.50 and $36.76 respectively (plus rather expensive shipping).

The grid-dip meter was a kind of cool toy:  it is basically just a one-tube radio frequency oscillator, but when it is placed near an inductor that is part of another resonant circuit, you get a dip in the current in the grid of the tube when the frequencies match.  Why is that cool? Because you can mess up the images on TV sets by using the broadcast frequencies, the IF frequencies of the receiver circuits, or the frequencies of the raster scan. I believe I had a KnightKit G30 grid-dip meter:

I found that someone has scanned in the whole assembly manual for the Knight G-30.

Schematic for Knight G-30 grid dip meter.

The schematic for the Knight G-30 grid dip meter. Note the simple one-tube oscillator circuit. Image shrunk from scanned copy at http://victrolla.homeip.net/wo5s/junkpile/knight/g30/pages/30.gif

I’m not sure what model of vacuum-tube volt meter we had.  The closest match I can find to my memory is the V-7, but it doesn’t match my memory exactly.  I seem to remember only banana-plug inputs.  Perhaps some historian of Heathkits could help me figure out which model we had.  It was bought before the oscilloscope and the grid-dip meter, I believe, if that helps narrow the time period.

My Dad, my older brother, and I spent a lot of time building the Heathkits, but that wasn’t all the engineering education I got.  I can remember my Dad bringing home a coil winder from work, and we spent some time making our own iron-core transformers (though I forget now why we were making them).

Morris coil winder

I don't remember exactly what coil winder my dad brought home from work, but it looked a lot like this picture of a Morris coil winder from http://www.pavekmuseum.org/radiowkshp2010/morriswinder.jpg

It wasn’t just in electronics that my Dad supported my education.  He also bought the family a beautiful old microscope, which he recently shipped to me for my son to use. Unfortunately, there were some heavy things in the same box, and mirror got broken.  Does anyone know where I can get a replacement mirror for an Ernst Leitz Wetzlar microscope (from about 1930)?

Ernst Leitz Wetzlar microscope

This is the beautiful old microscope that I used in high school. I would like to restore the mirror that was damaged in shipping.

Since it is now science fair season (I judged one school fair last week and will judge another one this week, though the County Science Fair is still a month away), I would be remiss in not mentioning how Dad supported us through our science fairs.  I can only remember three projects now, two of mine and one of my brothers, but I’m sure there were others based on things we read in the Amateur Scientist columns of  Scientific American.  I read Amateur Scientist and Mathematical Games every month, even when the rest of the magazine was not interesting to me.  I now have the full collection of Amateur Scientist on CD-ROM, but reading it on-screen does not have the same appeal as turning to the back of the glossy magazine, and I have not done more than glance at the columns on the CD-ROM.  I tried re-subscribing to Scientific American a few years ago, but it had become like People in science, and I found it a complete waste of time.  I’ve done better with Make magazine and IEEE Spectrum.

Two of the science fair projects I remember could not have been the same year, because both involved the same piece of equipment: a cheap portable record player, which we used just as a constant speed motor.

  • My older brother hooked up a 3′ or 4′ wooden arm to the turntable, with wheel at the end, to get a wheel that moved at constant speed along a circular track.  He then piled sand on the track and experimented with making road corrugations.  I forget what the independent variables were—probably speed and weight, but the apparatus did make cool corrugations in the sand track.
  • I used the same turntable with a cardboard and aluminum foil disk and some stranded wire for brushes to make a low-frequency square-wave AC signal from a battery.  The power then went to two carbon electrodes (scavenged from dead batteries) in salt water, and I measured the hydrogen and oxygen released by DC and AC currents in some glass funnels with long tubes.  Unfortunately, the slowest speed of the turntable (33 1/3 rpm) produced 0.555 Hz, which was still too high a frequency to get any electrolysis, so I ended up using a DPDT switch and manually reversing the current about every 10 seconds (0.05 Hz).

The other project I remember was one on vortex rings (the fancy name for smoke rings).  We drilled a 1″ hole in the bottom of a coffee can, and tapped the lid to get very neat smoke rings.  The smoke was generated by burning tobacco in a corncob pipe.  We rigged a Raleigh bike pump to suck air instead of pushing it (just reversing the leather cup washer on the piston), so no one had to directly breathe the smoke.  I remember that the clear tubing got really disgusting buildups of tar—this project may have contributed to my never smoking, despite the coolness of smoke rings.  Nowadays one can buy a Zero Blaster with non-toxic smoke or an Airzooka to get really big vortex rings, but in those days there was no off-the-shelf solution.  I don’t remember what I did with the smoke rings now, though I do remember that I had made a cardboard shield with a Lucite window to view the smoke rings in still air.

As an engineering professor, I often find myself saying to students things my Dad said to me.  One of his most popular responses when asked “what would happen if … ?” questions was “Try it and see.”  I find myself telling that to senior design students who have been dragging their feet on their projects, uncertain how to design something and wanting someone to hand them a solution.

Besides science and engineering, my Dad taught me many things that are still important to me today.  For example, he taught me to ride a bicycle and do simple maintenance.  My bicycle is now my main means of transportation, and I ride a couple of thousand miles a year commuting to work.  Dad and I have done a couple of self-contained (camping) long-distance tours together: in 1992 from his house to the League of American Wheelmen rally in River Falls, Minnesota, together with members of his bicycling club and in 1994 from my house to North Hollywood, 466 miles down the California coast, together with my nephew.  We also attended a League of American Wheelmen Rally in Flagstaff, Arizona in 1988 that included a supported ride to Sunset Crater and Grand Canyon.

I couldn’t remember when the Arizona ride was and the League of American Bicyclists has a terrible web site with almost no historical records. After wasting a lot of time searching the web without finding anything useful, I switched to the older technique of looking at paper records.  I found my log book for the solo ride I took in 1991 from the Rally in Olympia, Washington back to Santa Cruz, which was my first self-supported tour, and the log book mentioned that I had done the Arizona ride “some time ago”.  Luckily, I had paper copies of the L.A.B. and L.A.W. newsletters back to 1987, so I found out when the Arizona Rally had been fairly quickly.

Although Dad and I have shared a love of cycling, I’ve never acquired his love of swimming.  I learned how to swim as a child, but never really enjoyed it.  Part of the problem was that I was a very skinny child with almost no subcutaneous fat, so I got seriously chilled after just a little while in the water.  Now, I’m verging on overweight, so perhaps I should try swimming again.  Of course, the ocean here is far too cold to swim in without a wetsuit, and the City pool has been closed due to budget cuts for over a year.  I don’t think I want to pay the high prices the University charges faculty to use their pool, so it is unlikely that I’ll be taking up swimming any time soon.

Disclaimer: I received no compensation for plugging any of the products depicted on this page. If someone wants to send me free electronic test equipment or a coil winder, let me know.

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