Monthly Archives: March 2020

Science Fair Idea: Eli the Ice Man

If you ask any serious student of electricity to name their favorite ice man, they’ll undoubtedly tell you that it is Eli. Eli the Ice man (a friend of Roy G. Biv) is a mnemonic to help you remember that in an inductive circuit (L), the voltage (E) leads the current (I). And in a capacitive circuit (C), the current (I) leads the voltage (E).

You can prove this concept with this simple experiment shown 75 years ago this month in the March 1945 issue of Radio Craft. In addition to the capacitor and inductor and a few miscellaneous parts, you’ll need a voltmeter and ammeter. During the war, those analog meter movements would have been hard to come by, but these days, you can get buy with two cheap multimeters. Stores sometimes give digital meters away for free, but this experiment will look a lot cooler with an analog meter.

You wire up the circuits and then observe the meter when the current is turned on. In the capacitive circuit, the ammeter will move before the voltmeter. In the inductive circuit, it will be the other way around.

COVID-19: How You Can Help

As I write this from the safety of my home, millions of workers are literally risking their lives to serve their country. The obvious ones include healthcare workers, police officers, firefighters, paramedics, and National Guard members. But just as important are the bus drivers, postal workers, delivery drivers, truckers, grocery store workers, warehouse workers, factory workers, and countless others who are making sure that the public has access to the goods and services needed to sustain life. They are risking infection to serve us, and they deserve our respect and our thanks.

Others, like my wife, a medical interpreter, are able to provide needed services from the safety of their own homes.

And then, there are a lot of people like me, who don’t have any vital services to perform. Many are wondering what they can do to help, and there are a number of opportunities.

My wife and daughter have been busy making surgical masks such as the ones shown above. They are made according to instructions posted online by one of our local hospital systems (see below). One of our neighbors supplied some of the materials, picked up the finished masks outside our door, and delivered them to the hospital, where they are being picked up curbside at a designated location. These masks will be used in less critical situations by staff and patients in order to conserve the N-95 masks that are in dangerously short supply.

I know at least two friends with 3D printers who are making other needed products, such as

Face shields being 3D printed. Courtesy Don Seiford.

face guards. American factories can’t meet the demand for these lifesaving supplies. But the millions of Americans who own equipment such as sewing machines and 3D printers can help meet the need until American industry ramps up its production.

Virtually all health care facilities are in need of supplies. Many will have their own particular requirements, so it’s probably best to contact them first (checking their website first is probably best, so that staff doesn’t have to spend valuable time answering the phone).

Check neighborhood social media sites, such as neighborhood pages on Facebook or NextDoor. Chances are, some of your neighbors are already working on needed items. Coordinate with them to share materials. In addition to hospitals and clinics, items are needed by dentists, nursing homes, assisted living facilities, home health care agencies, and probably many others. Some of these institutions are non-profit, and some are for profit. But it doesn’t matter. They need supplies, and they can’t get them. They are counting on you. If you honestly can’t find anyone who needs them, then send me an e-mail, I’ll give you my mailing address. You can make the masks shown below, send them to me by U.S. Mail, and I’ll make sure they get to a hospital in my area. But chances are, the need is just as acute in your area.

Do not have direct contact with people outside your own household. Do not go to a store to buy supplies. Use the materials that you have at home, or that can be safely delivered by neighbors leaving outside the door. The idea is to be of service, and you will be of no help if you get infected or infect someone else. Be part of the solution, and not part of the problem.

Here are some opportunities for you to serve:

1. Making Surgical Masks

If you have a sewing machine and know how to use it, your skills are desperately needed. My wife and daughter are making the style shown above, which are destined for Blue Cross Blue Shield and Allina. More information and complete patterns and instructions can be found at this link: https://blog.bluecrossmn.com/covid19masks/

North Memorial Hospital in Minneapolis has a different pattern, which you can find at this link: https://northmemorial.com/covid-19-donations/ North Memorial also has a mailing address shown on this site. So in the unlikely event that you can’t find someone locally to take the masks, you can mail them. Do not go inside the post office to mail anything. You can buy postage online and leave the item for your letter carrier.

Update: The following website allows you to search by zip code for facilities in your area that need masks and other supplies. In the unlikely event that you don’t find anyone locally, it also lists facilities that you can mail them to:

https://www.donategoodstuff.org/covid-19-crisis-how-you-can-help.html

The Facebook group mentioned below also contains patterns for an isolation gown. I don’t know of particular hospitals that are requesting these, but there’s apparently a need.

2. Help Sewers and/or Donate Materials

Even if you don’t know how to use a sewing machine, others in your neighborhood probably do, and they are probably working. They also need unskilled help from people like me to cut the fabric to the correct size. Also, if your household, like many, has a stash of old sewing supplies, it’s very likely that your neighbors need these items to make masks. A critical shortage in our neighborhood was the elastic. If you have some in that box of old sewing and crafting supplies, your neighbors probably need it. The other need is new 100% cotton fabric.

3. 3D Printing

I know that persons with 3D printers and similar equipment are using them to make face shields and other needed medical supplies.

If you are able to help, a Facebook group named “Open Source COVID19 Medical Supplies” has formed and is coordinating these efforts. I’m aware of the face shield plans at this link:
https://3dverkstan.se/protective-visor/

Prusa Research has the following information regarding face shields at its Facebook page:

4. Lending Your RV

If you’re an RV’er, it will probably be a while before you’re able to go camping. Consider lending it to a medical professional who needs to be isolated from their family. This is being coordinated at this Facebook group: https://www.facebook.com/groups/rvs4mds/

Cutting Your Hair During Quarantine

The State of Minnesota is now under a “stay at home” order, and many other areas now have similar restrictions. Non-essential businesses, especially ones which require close personal contact, are closed. And even if they were open, I wouldn’t want to see a barber right now. The close contact would make it likely that they would infect me, even if asymptomatic, or that I would infect them.

Unfortunately, for about a month before the lockdown, I kept thinking to myself that I really needed to get a haircut. I’m a procrastinator, and I never got around to it until it was too late.

Fortunately, I had at home one of the handy gadgets shown above, the Conair hair trimmer. I don’t do as good a job as a professional, but I can keep my hair from getting out of control. I suppose if I were desperate, I could just get out a pair of scissors and give myself a bowl cut. But the trimmer shown above does a much more subtle job. It comes with instructions, but you basically just comb it through the part of your hair that you want to trim. I’ve found that it works best to do it gradually, by cutting my hair a little bit each day. Fortunately, they’re readily available, and you can add one to your next Amazon order for just a few dollars.

Update: If the model shown above is out of stock, the one shown below appears to be very similar. It doesn’t look like it’s made quite as well as mine, but should do the job. A number of the reviews say that it isn’t sharp enough, but it also looks like it takes standard safety razor blades (the old-fashioned kind), also shown below. Fortunately, those blades are dirt cheap, and I would recommend ordering some of them as well. In fact, you’ll have plenty of extra razor blades, so you might want to try using one to make a foxhole radio.

Coil Winding Hints

According to the March 1935 issue of Popular Science, if you had asked any constructor of a shortwave receiver what the most difficult step was, you would have been told that it was winding the coils. Fortunately, the magazine had some pointers. And since, today, you can’t just walk into the local radio store and buy a set of pre-wound coils, the advice is timely for those who want to build an old-time set.

The first step is obtaining the coil forms. Of course, they’re also unavailable today. But during the depression, there was economic incentive to save a few cents wherever possible, and the magazine showed you how to make your own. You did that by finding an burnt out tube and using its base for the coil. The first step was to remove the glass, and for this, there were two methods. You could soak the tube in water to loosen the cement, and then twist out the bulb. There was also the tried-and-true method of taking a hammer to the glass, as shown in the illustration. The magazine cautioned that covering the tube with cloth first was an important safety precaution.

As for the actual winding, the magazine showed two methods to maintain tension but still have two hands available to wind and guide the wire. You could put a weight on the end of the wire, or use the “walking up” method by putting the end of the wire in a vice, and then walking toward the vice while winding.

Surgical Mask for Smokers: 1919

Masks during a pandemic are nothing new, as shown by this illustration during the Spanish flu epidemic.

Shown here is Edward T. Duncan, modeling his invention, an influenza mask suitable for smokers. To the standard issue mask, he affixed two corn plasters, one on the inside, and one on the outside. A hole is poked, and the cigar or cigarette can be inserted.

“When you draw on your cigarette, all the little germs hovering around take advantage of the chance and try to get in. But when they have gone through the fire of your cigarette they become purified, and are quite harmless by the time they get to your lungs.”

When not smoking, the hole was plugged with a cork.

This invention appeared in the May 1919 issue of Popular Science.

1945 Crystal Set

Seventy-five years ago this month, the March 1945 issue of Radio Craft showed this crystal set idea, sent in to the magazine by John Haynes of Doe Run, Missouri. The coil, consisting of about 125 turns of wire, was mounted on a coil form slipped over an old shield can, and snugly affixed with gummed paper. A second can slid over the coil, and was adjusted to tune the set.

The magazine noted that a similar idea appeared in the January 1943 issue of the magazine.

1935 Light Beam Communicator

85 years ago this month, the March 1935 issue Popular Mechanics showed how to make this light communicator, said to have a range of about a half mile.

The receiver used a caesium photo cell, which the magazine said could be had for about $3. This was fed into a two-tube amplifier which could drive a speaker or headphone.

For audio amplification at the transmitter end, the system used the household radio receiver, and the magazine explained how to hook up the microphone. The the light beam generator used a system I’ve never seen before. Instead of electrically modulating the light bulb, a mechanical approach was used. The speaker was disconnected and the output was instead connected to a magnetic headphone that had been modified. The outer cap of the headphone was unscrewed and cut so that most of the metal diaphragm was visible. Then, the “diaphragm is slipped off and taken to any plating firm to be finished in the same manner as an audio headlight reflector.” The headphone was reassembled, and the result was a mirror that would vibrate in time with the sound. An auto headlamp was used to illuminate the mirror, and this was focused through a lens with a focal length of about 12 inches.

The result would have been a narrow beam of light that was modulated. At the receiving end, another lens was used to focus the beam on the photo cell.

For a unique science fair project, the advanced student could adapt this project using modern materials. When I was a kid, I built a similar system using a flashlight as the transmitter. The bulb was wired in series with the secondary of an audio transformer. The primary was fed by the output of an amplifier.

For the receiver, I used a solar cell fed directly to the input of an audio amplifier.

Testing a Battery with a VOM

Fifty years ago, Electronics Illustrated showed this pointer for testing batteries with a multitester. Just measuring the voltage won’t do much good, as the battery will probably show its full voltage, even if depleted, with no load.

The solution is to put a resistor in parallel across the battery. If the battery shows full voltage across this 100 ohm resistor, it’s probably good.

These days, multitesters are even cheaper than they were 50 years ago. In fact, occasionally stores will give them away free. If you don’t have one around the house, get one, as you won’t know what you did without it.

Some of the meters below give you an idea of how inexpensive they are these days.

If you don’t have that 100 ohm resistor in your junque box, you can also get it on Amazon.

Some links on this page are affiliate links, meaning that this site gets a small commission if you make a purchase after clicking on the link.

Cub Foods Grocery Pickup Review

During the pandemic, my family is minimizing as much as possible direct contact with others. We’re staying home, going out only when necessary, and staying away from other people when we do go out. To purchase groceries and other items, we’re ordering online. Earlier this week, I reviewed our experiences with Walmart pickup.

Today, we picked up an order from a local supermarket chain, Cub Foods. We had to chose a pickup slot about five days out. We placed a small order initially, and kept adding to it during the week. For our Walmart order, we had to make any final changes about 12 hours before the pickup time. With Cub, we were able to make changes up until the last minute.

When our order was being shopped, we received a text alerting us. We were able to log in to the app (or to the website, which I used) and chat directly with the person doing the shopping. When a product was out of stock, we were given a suggestion for a replacement product which we could either accept or decline. In a couple of cases, she texted us and asked for our choice.

A few items (rice, hand sanitizer, and toilet paper) were completely out of stock, and we were informed. We were informed when she was finished, and at the store, we alerted them that we were there using the app. The employee loaded the groceries into our car, with no personal contact needed. Unlike at Walmart, we didn’t need to sign in, and it was possible to stay back several feet.

One big advantage of Cub was that the whole pickup took place without any close contact with the employee. We opened the door, and he loaded the groceries. At Walmart, there was the additional step of having to sign for the order on a small tablet computer, meaning that there was some chance of contamination. Update: As of March 25, Walmart is no longer requiring you to sign for the order. At Cub, you identify your car on the app (including the license number), so there is no need to sign personally. The employee simply comes out to the right car and delivers your groceries.

Walmart had two advantages over Cub. First of all, it was possible to get a slot slightly sooner. It appears that slots open up at midnight (local time, I’m guessing) and you can make reservations for the next day. It appears that with Cub, you need to make the reservation about five days out. Also, with Walmart, it appears that you can purchase any item in the store. So if you need items such as hardware, electronics, or even clothing, Walmart would be the best option. Since Cub is a grocery store, you’re limited to mostly groceries. (However, like any major supermarket, Cub always has a small selection of non-grocery items.) Also, Walmart has somewhat lower prices overall.

Despite those advantages of Walmart, we preferred Cub. Being able to communicate with the shopper with respect to substitutions was a very nice touch. If you think of an item at the last minute, you can add it in.

At Walmart, most of the substitutions were very reasonable, and we did have the opportunity to reject them. But there was no mechanism to ask for a different replacement. With Cub, that was possible. At Walmart, you reject any substitutions when you’re picking up your order, with no opportunity to get a different replacement.

To chat with the shopper while your order is being filled, you of course have to be available online at the right time. When life gets back to normal, perhaps that will be difficult. For the time being, though, that’s not a problem.

Of course, unlike at Walmart, nobody crashed into our car when we were picking up items at Cub. But that’s hardly the store’s fault. We’ll probably use Walmart again if we’re in more of a hurry or need non-grocery items. Their service was very good. But for most of our grocery needs during this crisis, we’ll probably rely on Cub.

Some links on this page are affiliate links, meaning that this site gets a small commission if you make a purchase after clicking on the link. The links to Cub, however, are not affiliate links, and we are not compensated if you use them..

1945 One-Tube Four-Stage Receiver & SW Converter

Seventy-five years ago this month, the March 1945 issue of Radio Craft magazine carried this one-tube receiver, submitted to the magazine by Sgt. L.R. Blattner, who was stationed at Tinker Field, Oklahoma. According to the serviceman, the set gave the maximum performance for the number of components, and it’s hard to dispute that claim. Despite having only one tube, the set had a stage of RF amplification, AVC, and two stages of AF.

The signal is first applied to the pentode section of the dual tube, passed through the RF transformer, and then detected by the plate and cathode of the triode. Then, it’s applied again to the pentode, now acting as an AF amplifier. From there, the signal goes back to the triode where it’s amplified again.

The magazine also carried the shortwave converter below, sent in to the magazine by Richard E. Held of Sioux City, Iowa, who reported that he received stations from Tokyo to Brazzaville. It tuned 7-11 MHz, and used two tubes that the writer had lying around.

OneTubeRadio.com

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