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Ripple Voltage Monitor Answered 2019 Issue-6

I need a circuit to monitor the AC ripple voltage on a 12 volt linear power supply? A digital display would be ideal.

Brian Lambdin
Plano, TX


Mr. Lambdin inquired about a circuit to monitor the AC ripple on the output of a linear power supply.  The inference is that the frequency response of the circuit need not be excessive. He also wanted a digital display.

I found what ought to be a suitable device, in kit form, from Amazon, for $29.95. See https://www.amazon.com/Oscilloscope-Handheld-Pocket-size-Electronic-Learning/dp/B01LWK49W3/ref=asc_df_B01LWK49W3/?tag=hyprod-20&linkCode=df0&hvadid=309778489815&hvpos=&hvnetw=g&hvrand=18068906155916055584&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1018200&hvtargid=pla-465542683176&psc=1

Peter A. Goodwin
Rockport, MA

In a linear supply the vast majority of the ripple will be at the input frequency which will normally be the power line frequency (50 or 60 hz) or two times that frequency (100 or 120 hz.) A digital multimeter on the AC volt ranges is intended primarily for that frequency range. By blocking out the DC from reaching the meter any DMM set to the AC volt ranges should measure it fairly well. A "True RMS" type meter is best since the ripple probably will not be a sine wave.

To block out the DC part simply put a capacitor in series between the positive side of the supply and the positive input of the DMM. A value of 1 microFarad or more should work. If you use any type of polarized capacitor such as an electrolytic make sure to connect the positive end to the positive output of the supply. Of course, make sure the voltage rating of the cap is higher (16 or 25 Volts should be fine) than the supply. You may need to put a fairly high value resistor (say 10 K Ohms) across the meter leads (from the negative end of the capacitor to the negative side of the power supply.

William Cooke
Adams, TN

SPDIF Input 2020 Issue-1

I have some legacy recordings on DAT I’d like to re-edit as my skills have improved, but my DAT recorder has only a SPDIF digital output. My old XP box had this on the mother board, and all I needed was the back plate with the RCA jack and the cable to the pins on the board. Adobe Audition recognized it immediately.

Newer computers do not have SPDIF inputs. I would think converting the SPDIF serial stream to serial USB would be simple enough as far as circuitry goes, a lot simpler than an analog composite video (and S-video) plus audio to a USB device I can get for $30 with software. Perhaps a Windows 10 driver is is needed and is a challenge?

Every search only returns a flood of USB to SPDIF dongles, which is the wrong direction, and a few very expensive sound cards with many other unneeded functions. Is there a simple/inexpensive solution?

Dennis L Green
Farmington Hills, MI


Searching for "spdif input" under "Computers, Tablets, and Networking" seems to show a number of things like what you want. Here's the list: https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=spdif+input&_sacat=0 And here's one that looks useful: https://www.ebay.com/itm/184216799887?hash=item2ae42d4a8f:g:6jMAAOSwJ81gZjs1 They're in the $20-$40 range, which doesn't seem too bad.

Mitch Golden
via internet

I did a quick Google and found this in my second hit: www.amazon.com/Ebetter-External-Surround-Recording-Compatible/dp/B07BT6CM6Q Says it does SPDIF to USB when set for digital input. And it's under $20. I'm lucky, I still have a few SPDIF compatible sound cards from the late 90's/early 2000's that are PCI based, and PCs with PCI cards.

Ralph Phillips
Bossier City, LA

Gummy Lubricant 2020 Issue-1

I have an old Leitz Wetzlar Type 31575 slide projector that uses two solenoids for operation by a wired remote for advance and focus. Whatever lubricant was used has thickened too much after too long in storage, keeping the solenoids from operating without coaxing. They are accessible from the bottom access plate intended for lubrication of the associated mechanisms, but removal of the plunger is not possible without a total tear-down top to bottom, which is risky on old equipment with no manuals. I’ve had plastic gears shatter in similar equipment, so that will be my last resort. Wiping down the plungers was not adequate. Something stronger than alcohol is needed.

What sprays would be safe to try, preferably that come with a flexible straw, to dissolve and flush out the sludge? Contact cleaner, such as DeoxIT D5, has a lubricant. Would that interfere with the solenoid operation? Is Fluxoff a safe choice?

Dennis L Green
Farmington Hills, MI


I would differentiate between the situation where the volatile parts of the lubricant have evaporated (e.g. dried out) versus a scenario where the lubricant has become stiff due to adherence of dust to it. In the second case flushing it out would be warranted. Not sure what I would use in that case. It depends on if there are plastics in the immediate vicinity that could be damaged. I would probably try some CFC if you have any, otherwise a generic contact cleaner spray. I would keep cotton balls and swabs to blot up the excess as quickly as possible. WD40 is another option, but again, capture the excess or it will leave a residue. In the dried up case I have had very good luck using additional lubricant to loosen up the viscosity of the original without flushing it out. Unless the plunger is plastic it is highly likely the original lubricant is petroleum based. A very small amount of general purpose lubricant such as 3 in 1 sewing machine oil can be applied and worked in. Mineral oil (from the drug store) will also work. Even very small amounts of WD40 will work, but since it will fairly quickly evaporate (over a few months) you will need to combine it with the oil. If you believe that the original is not pertroleum-based, then a small amount of dishwashing liquid such a Dawn may help. I hope this helps.

Rolf Taylor
Springfield, VA

Electromagnetics: Transformers, Generators, Motors, and Other AC Machinery Answered September 2017

I’m trying to make sense of everything coiled, but the only thing getting wound up is me! I thought I knew a bit about electromagnetics, but recently I’ve been trying to make sense of all these fields and flows.

What is the difference between the magnetic field and the flux? How does flux work in a transformer or a generator? Does anyone really understand Maxwell’s Equations?

So many textbooks dealing with electromagnetism speak in equations instead of English. I want to know HOW it all works, not just how to compute these things. Am I just reading the wrong books? Can you help me figure out what the flux is going on?

Taylor Street
Felton, CA


I have spent a lot of my life wondering about magnetics. Welcome to the club! Hopefully the information that I have is correct

Here are a few basics:

  1. When an electron moves, it generates a magnetic field in addition to the electric field that's always there.  — Why?: Because
  2.The field exists if the electron/electrons move in a wire, a stream (e.g. in a tube), or anything else.
  3. Magnets 'work' because (if I have this right), the arrangement of their molecules is such that the electron orbits of the individual atoms are oriented such that the fields generated add together. The relative strength of a magnetic material is based on how well they are aligned. Magnet discussion usually describes magnetic domains within the material. (Magnetizing a material means that you apply a magnetic field to align the domains.)
  4. Non magnetic materials don't feature this alignment. Electron orbits are in random orientation and the fields cancel.
  5. Magnetic fields are constant for DC current and non moving magnets.
  6. Time varying fields are generated from AC current and moving magnets.
  7. Time varying fields do the following: A. If they pass through a wire they will cause the electrons to move — thus a transformer. B. If they encounter another magnetic field they will cause either an attractive or repulsive force — thus a motor. (This force is also present in static field interactions, but that won't make a motor.)
  8. Coils of wire are used in transformers and motors because the fields add and compact devices can be made.
  9. The field descriptions are always confusing. What I got out of it was that the B field is the description for the field you would find due to the current or magnetic material. The resultant field that you can measure depends on the material that the field is in.

Exmple: If you have a long solenoid, the field inside will be fairly constant if you're not too close to the ends. If you put a piece of ferrous material inside, there will be an increased field through the metal because it's easier for the 'flux' to go through this material. (This also affects the input current to some extent, in the same way that a a lower resistance load affects an electric circuit.)

  10. There seems to be no end of magnetic units — just like farenheit, centigrade, and Kelvin for temperature.
  11. Maxwell hopefully understood his equations, along with some other smart people.

The math that you see everywhere generally shows what fields you can expect due to different circumstances. It is very difficult, and I certainly don't understand it. Happily, computers are now available that are powerful enough to avoid a lot of it. They use a method called finite element analysis. Basically they calculate fields based on the sum of tiny elements at each point of interest in a field.

Harold Johnson
via email

Car Detection Answered 2019 Issue-5

I’m looking for help designing a circuit to detect cars driving up my private road. I have in mind something like the wire loop embedded in roads to sense cars at a traffic light. Can you explain the principle behind this method and how a basic DIY version might be implemented?

Ulrike Krüger
Laconia, NH


A Passive Infrared (PIR) detector is much less expensive and easier to use. There are many available for outdoor use, with battery operation and remote monitoring by Wifi or other means. I don’t know of any DIY road loop circuits, and they are being phased out due to high installation and maintenance costs in favor of cameras, which are another choice.

I once bought a little board from a guy in Australia which monitored standard NTSC video and detected movement. Worked pretty well.

Richard Cox
Thousand Oaks, CA

Diesel Computer Mods Answered 2019 Issue-5

There are several entities that will modify the settings on the engine control computer for a diesel Chevy pickup to increase power. I assume they are adjusting the timing curves and other parameters. Is there an adapter and software available for me to experiment with this myself?

Karel Dostál
Covina, CA


I really hate to be a wet towel, but this is really not a good idea. Arbitrarily adjusting things like fuel and timing is most likely to result in a smoking, noisy engine. If run to long the engine is more likely to self-destruct than increase power. Not to mention tailpipe pollution. Even "professionally" reprogrammed engines emit excess pollution, and shorter lifespan.

Bill van Dijk

Guitar Tuner Answered 2019 Issue-5

I’m trying to build an electronic guitar tuner. Is there an IC available to generate the proper tones?

Hamish Morisset
Norcross, GA


I would suggest an ebay search for guitar tune”. There are several listed in the ten dollar range with free shipping. The tuners don’t generate a tone but receive a tone and show the note on the lcd. I think parts cost for self build would be higher than purchase.

Steve Benson
New Castle, IN

Dish Projects Wanted Answered 2019 Issue-5

I have a couple of small satellite dishes (Direct TV I think) with receivers that have been sitting in the garage for a while. I hate to throw out technology that could be repurposed. Anyone have an idea for a cool DIY project I could reuse them for?

Devin Martel
Durham, NC


Make a long distance microphone like they use at football games. Mount a microphone at the focal point and connect to an audio amp and headphones.

Richard Cox
Thousand Oaks, CA

Solar Panels And Lightning 2019 Issue-4

Are solar panels suceptable to damage by nearby lightning strikes and would they provide any margin of safety to electronic equipment in a grid-tied or off-grid system?

Alex Freeleagus
Tigard, OR


While a direct hit will wipe out just about anything, a nearby hit won't do much damage to a solar panel. If something were close enough to get a shock, electronic gear would be the least of your trouble! Just use proper grounding per NEC codes. (and fuses)

Robbie J
Green River, WY

NFL Magic Lines 2019 Issue-4

Can someone explain how the first down and scrimage lines are generated on screen in televised NFL games? Obviously, it's done by computer, but I can't figure out how the angle and aspect is able to change and keep up with the constantly changing camera angles. Also, the lines are seemingly underneath the players, as if they were actually drawn on the ground.

Ryan Johnson
Jackson, MS


If you’re in Alexandria VA, you can go to the National Inventor’s Hall of Fame museum and they have an interactive exhibit about it: https://www.invent.org/museum/exhibits

“1st & Ten Line Stadium
Get in the game with the 1st & Ten Line Stadium exhibit, inspired by several game-changing NIHF Inductees. Visitors can step onto the turf to experience the sounds and visuals of a real football game. This hands-on exhibit puts you on the big screen, as you control the placement of the Virtual Yellow 1st & Ten® line, invented by Inductee Stan Honey.”

ESPN Front Row has an article about it that has additional links to the history of the system:


I hope that helps give Mr. Johnson some resources to read.

Phil Gates
via email

The short answer is the TV broadcaster maps out the stadium and instruments the cameras to report exactly where it is focused (tilt, pan, zoom, and focus). Computer processing then overlays the first-down (yellow) line onto each frame of the video. There is a good write-up on the technology here: https://entertainment.howstuffworks.com/first-down-line1.htm.

Kerry Imming
Rochester, MN

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