Everything for Electronics
Nuts & Volts Magazine (January 2020)

Reader Feedback (01.2020)

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Comments on the Issue-5 2019 article, “LEDs for Operational Status and Troubleshooting” by Klaus Spies

As a designer of electronic systems that used microprocessors and a variety of IC circuits, I always sprinkled a collection of LEDs on the circuit board for diagnostics. I was sometimes overruled since LEDs cost pennies, but in production work pennies are not allowed by the number crunchers. When overruled, I would try to assure the pads (or holes) for the resistor LED would remain for test probing during troubleshooting.

Paul Haug

The use of LEDs likely could be called an operational use, however, we refer to it as a safety or “SAFE” indicator.

A friend of mine and I design and build model rocket launch controllers for youth to use. The simplest version uses a single 12V 30A contact rated automotive relay. Should the NO relay contacts “weld” closed, it would result in a launch as soon as the clips were connected to the igniter.

As a safety (SAFE) indication, he added a yellow LED and resistor in series with the NC contacts to indicate the relay had returned to the normal contact position. A red LED and resistor is also used in series with the NC contacts and the igniter as a continuity indicator.

The test current for the continuity LED is designed to be less than 20 mA with measured currents typically on the order of 15 mA to 17 mA.

The three-rod version uses three relays, three SAFE LEDs, and three continuity LEDs with individual rod (relay) enable switches in series with the relay coils. Three of these controllers have been in use for over 10 years now, providing launch control for several different TARC teams.

G. Shaiffer

Comments on the Issue-5 2019 article, “Newton’s Apple” by David Goodsell

Great article! Great mix of disciplines (analog/Arduino/mechanical). Pet peeve: Newton’s original equation was F=dP/dt (the ‘P’ is the Greek Rho, for momentum). However, momentum=mass x velocity, and he errantly assumed mass couldn’t change. So, he re-wrote it F = M x (dv/dt), which is acceleration. So, the next question is, how much mass did the ball gain as it fell?

With all respect, I just started watching the Mr. Carlson’s Lab videos, also multi-discipline like your article. You’re doing the next generation a great service.

George Bernius

I’m a retired laser systems engineer from Lockheed and enjoy working across a number disciplines. My dad was a mechanical engineer and it warped me. I’m happy as a clam when I’m working on a part with the milling machine. Although some programming languages give me fits. Whatever happened to punched IBM cards? I too watch Mr. Carlson’s lab and love it. I’ll give the “mass gain” factor that you mentioned some serious thought and get back to you in a year or so. Thanks for the good words. Keep safe!

Dave Goodsell

Answer to the question: Of course you band sawed the box! Awesome article! Incredible device! Congrats on a superb job.

Zmrotu Zargon

Glad you enjoyed the article. It was a fun project, sorta. Although at times, I wondered if it would ever get finished. I called it, “The project that would never end.” Yes, I band sawed the case. BTW, that extra little gap at the bottom served as a drain for any extra electrons that got loose in the case.

Thanks for your kind comments.

Dave Goodsell

That is a great project! This was a fascinating read. We may be kindred spirits ... I also did an experiment to measure the Earth’s gravitational field in my house back in 2009. I used a pendulum that moved back and forth, interrupting a laser aimed at a photodiode; see http://cosinekitty.com/pendulum.

The theoretical value for where I live is 9.7922 m/s^2. My apparatus determined 9.7901. I learned a lot about calculating the moment of inertia of a real pendulum, as opposed to the idealized pendulum where all the mass is concentrated at a point. Also, I made my own thermally calibrated timing circuit that I did my best to synchronize with NIST time servers. I didn’t realize, like you did, that I could buy a calibrated ruler. I used a tape measure from the hardware store. LOL.

So, if I could make my dream device, I would use a GPS-based frequency standard for timing, an evacuated chamber for the pendulum (WOW!!!), and a calibrated ruler too.

The advantage of a long pendulum is that it moves back and forth a lot slower than something that drops, giving you a longer time interval to measure. Of course, the disadvantage over dropping an object is that it adds more variables.

Was there any uncertainty in how long it takes for the electromagnet to let go of the ball? I suppose by having multiple beam crossings, it doesn’t matter. Have you considered using laser pointers instead of LEDs to make tighter beams? Again, great article!

Don Cross

Wow! Your pendulum experiment was cool. I loved “the concrete in a can.” Looks like you had to work through a number of configurations to get a good result. I know the feeling. Congrats.

Regarding the electromagnet release time, yes. It varied, but it didn’t really matter because it was the deltas between the sensors that counted. Plus, I had four photogates which allowed averaging.

Initially, the whole idea of the experiment was to use the surplus photogates I found on eBay. Silly me. If I had just built the sensor system from scratch, I would have designed an optical system with less divergence. However, by inserting the apertures, the beam profile was good enough for this application. Thanks for your interest and suggestions.

Dave Goodsell

Comments on the Issue-4 2019 article, “The Story of the Transistor” by George Steber

Built my first amplified crystal set using the Raytheon CK722. I was 11 and mowed lawns for money. That transistor set me back $7. That was a fortune to me. I used a germanium diode for the detector. A year later, I got a job after school making more money. I bought some of the first miniature solar panels. I then powered this little one transistor radio with solar power. A very long time ago in 1954.


Great article! I knew about Bardeen, Brattain, and Shockley, of course, but I knew almost nothing about the earlier work of individuals attempting to create electrical amplification. Thanks for such a thoroughly researched article.


Here’s a story that could be turned into a movie (or series) that I would love to watch.

Euclides Rezende

Bucking the System

Regarding Adhith M’s “Build a Pocket-Sized Vacuum Cleaner,” I don’t understand the use of the buck converter. It can only reduce the incoming voltage — great for a power brick, but the LiPo power setup is only 3.7V nominal. That converter can’t work at all at that voltage; let alone put out 7.4V.

If the two cells were in series, making 7.4V nominal and directly applied to the reverse switch, that would work, but you’d need a two-cell BMS and a different charging scheme. (Another smaller buck converter to feed the new BMS 8.4V to charge from the power brick input. And some rewiring on the output switch.) Fun idea!


Thank you for your valuable comment. I’d like to give you an explanation on the topic.

The buck converter is a CC/CV converter. So, along with regulating voltage, it also deals with acting as a constant current source for driving the motor. Like I mentioned in the article, these high speed motors do get heated up quickly and is kind of over-powered. So, reducing the current from the rated 4.2A to 3A was an important consideration to run the motor at the required level.

Coming to the battery pack, as you said, its a 3.7V nominal with two Li-ion cells in a parallel configuration (1S2P). The reason for this configuration is:

  1. 1S2P could be easily charged with the commonly-available TP4056 based charging module, whereas, adding two cells in series creates the complication of balancing each cell. So, a BMS with balance charging would be required. This consumes more space, which could be difficult to accommodate within the enclosure.
  2. If two cells are arranged in series, then the current draw through the cells would be 3A. I think it would exhaust the cells too much within less time.

However, in both the cases, i.e., series or parallel, a current regulating setup would be required. What you have mentioned is a very good point and I totally appreciate your valuable comment. I hope this is helpful.

Adhith M

Country Life for Me

Regarding Bryan Bergeron’s editorial on “The Challenging Life of Urban Hams” ... Stay out of a city or town if you want to be a ham radio operator. I made that mistake once in 1979, and never did it again. So much less hassle to live in a rural setting to be a ham operator.

If you earn your license in a city atmosphere, plan on low power operations forever, or move. You can fight city hall or an HOA, but plan on spending a lot of money on lawyer fees defying your neighbors or having a cop parked in your driveway to serve a subpoena on you.

Besides, it’s cheaper to live in a rural setting today. You might have to fight traffic some, but taxes and house costs are a lot lower, and interference is the cable/satellite/phone dealer’s problem (read Part 15 FCC Rules and Regs), not yours.

Fred Fuhrer III

Comments on the Issue-6 2019 article, “You Don’t Have to Be an Engineer to Design Your Own Electronic Circuits” by Lou Frenzel

This article is great! Love to see anything that encourages people to give it a try if they want. I have ZERO formal training in electronics, although I have always been a hobbyist/enthusiast, and now I have 30 years of self-taught experience.

I used to design my PCBs in Adobe Illustrator and used photo-resist etching at home to produce the physical product. I managed to design and build many pretty crazy electronics and very functional projects in the past. Now, I primarily use Eagle/Fusion 360 and order boards from OSHPark.com. But, again, no formal training. Just a thirst to learn it and use it to do cool stuff.


I also have over 30+ years fixing and building electronics. Many Arduino projects are still in operation around my home.

My goal this year is to rewrite all the code for all these projects to use either an ESP32, ESP8266, or WeMos D1 Mini. I just made my initial breakthrough using ESP, which I’m adding to my tried and true audio system controller.

This system has been used on a daily basis for going on three years. Out with the 2x16 LCD and in with the SSD1306 OLED, Si4703 FM tuner, and ESP8266 with IR output ... and did I mention that I will have a controller for a second room that will use ESP now to sync the current settings. There is still some challenges to get this synced, but I’m up to the task! I can’t remember how many electronics magazines I have subscribed to over the years.

Bob Durk