crystal radio

20 Articles

Credit Card Chip Used To Make Crystal Radio

June 1, 2020 by 23 Comments

Perhaps the simplest radio one can build is the crystal radio. Using a diode as a detector, the design generally uses less than 10 components and no battery, getting its power to run from the radio signal itself. [Billy Cheung] decided to build a crystal radio using a rather unconventional detector – the smart chip in a common credit card.

This is possible because the smart chip on many credit cards contains a diode. It’s then a simple matter of hooking up the right pads on the credit card to the rest of a crystal radio circuit, and you’re all set. Of course, [Billy] goes the whole hog, building the entire radio on a single credit card. Other cards are cut up to create bobbins for winding coils to form a variable inductor, used to tune the radio. Doing this allows for a much cleaner, thinner design, rather than using a variable capacitor which is comparatively hard to find. Turning the dial allows stations to be tuned in, and with a high impedance earbud hooked up, you’re listening to AM radio. Oh, and don’t forget an antenna!

[Billy] breaks down the details for anyone wishing to replicate the feat, going so far as to wind the coils in real time in his Youtube video. Cutting templates and other details are available on Github. While it’s not going to be the most replicated hack, as it requires the destruction of a credit card to achieve, we love the ingenuity. And, if society does collapse, we’ll all have a great source of diodes when the ATMs have all become useless. Video after the break.

[Thanks to Zane Atkins for the tip!]

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[Eric] Talks Crystal Radios

January 28, 2020 by 42 Comments

The AM broadcast band doesn’t have a lot of mainstream programming on it across much of the United States today. That’s a shame because a lot of kids got their first taste of radio and electronics by building simple crystal radios. [Eric Wrobbel] has a well-done page discussing some of the crystal radio kits and toys that have been around.

[Eric] should know, as he’s written two books on toy crystal radios. The pictures range from a 1945-era “Easy Built Radio Kit” which looks like a piece of masonite with a coil, some Fahnestock clips, and a cat whisker, to a very slick looking Tinymite from 1949. Honestly, though, the one we really want is the X-50 Space Helmet Radio that comes in a box marked “For Young Moon Travelers.”

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A Modern Take On The Crystal Radio

January 19, 2018 by 20 Comments

We’ll admit that [3DSage] has a pretty standard design for a crystal radio. What we liked, though, was the 3D printed chassis with solderless connections. Of course, the working pieces aren’t 3D printed — you need an earphone, a diode, and some wire too. You can see the build and the finished product in the video below.

Winding the coil is going to take awhile, and the tuning is done with the coil and capacitance built into the tuning arrangement so you won’t have to find a variable capacitor for this build. There is a picture of the radio using a razor blade point contact with a pencil lead, so if you want to really scrimp on the diode, that works too, and you can see how at the end of the video.

We did like the use of cord ends from a sewing and craft supply store to serve as solderless springs. This would be a great item to print off a few dozen copies and use it for a school or youth group activity. You might want to pair it with an AM transmitter, though so the kids won’t be dismayed at what is playing on AM in most markets. [3DSage] uses a sink for ground — literally a kitchen sink. However, if you try this, make sure all the pipes are metal or you won’t get a good ground and you probably won’t pick up any stations.

We’d like to get some of those springs and make some other kind of starter projects with them like the kits many of us had as kids. This reminded us of the old foxhole radios, found during World War II.

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Radio And Phone Speaker Has Style

February 22, 2017 by 7 Comments

Building a crystal radio isn’t exactly rocket science. Some people who build them go for pushing them technically as far as they can go. Others, like [Billy Cheung], go for style points. The modular radio and phone speaker looks like it came out of the movie Brazil. The metallic gramophone-like speaker horn adds to the appeal and mechanically amplifies the sound, too.

The video (see below) isn’t exactly a how-to, but if you watch to the end there is enough information that you could probably reproduce something at least similar. There are actually several horns. One is made from copper, another from paper, and one from a plastic bottle.

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High Impedance Headphones? They’re In The Can!

September 18, 2016 by 21 Comments

[George Trimble] likes to build crystal radios. The original crystal radio builders used high impedance headphones. In modern builds, you are as likely to include a powered amplifier to drive a speaker or normal headphones (which are usually around 4 to 16 ohms).

[George] builds his own speakers using chile cans, some wire, a few magnets, part of a Pepsi can (we are pretty sure someone will leave a comment that Coke cans sound better), and the iron core out of an audio transformer. You can see a very detailed video of the process, below.

There is a little woodworking and hot gluing involved. The result is decidedly homemade looking, but if you want to say you built it yourself (or, if you are a prepper trying to get ready to  rebuild after the apocalypse and you can’t find a cache of headphones) this might be just the ticket.

Most of the headphone hacks we see start with a pair of headphones. That’s a bit tautological, but the goal is usually to add features, not make the whole thing. It does give you some hacker cred, though, to be able to look at the other guy’s radio and say, “Oh. I see you used commercial headphones.”

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High Performance Crystal Radio

September 16, 2016 by 13 Comments

When you think of a crystal radio, you probably think of something simple maybe built out of household scraps. Not if you are [Chris Wendling]. He recently posted a video (see below) of his high-performance crystal set. He doesn’t take any shortcuts: he has several hundred feet of antenna wire, and uses a cold-water pipe ground system. With no amplifier, a strong signal input is crucial.

The radio has four subsystems: an antenna tuner, a bandpass filter, a detector, and a powered audio output system. He also has a truly enormous system of speakers on the ceiling–this isn’t the crystal radio you made in the boy scouts.

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PhD Crystal Radio Has Pizza Capacitor

May 26, 2016 by 35 Comments

Crystal radios are old news, but great fun. What would happen if a PhD designed a crystal set? By PhD we mean Pizza Hut Deliveryperson and [John Greenlee] (who may not actually be a PhD of either kind; we don’t know) gives us a good idea with his crystal radio in a pizza box.

Pizza boxes aren’t the only food-related material in this radio. [John] makes a tuning capacitor out of cake rounds. Coincidentally, he decorates the tuning capacitor to look like a pizza.

The schematic itself is unremarkable–just a common crystal set. But the construction of the chassis and the capacitor make it an interesting project. If you know a young person that has any interest in radio, a crystal receiver is a rite of passage you shouldn’t deny them and this one is certainly a novelty. The picture of a pizza takes it even one step further than this YouTube build, which is nonetheless a good resource.

The instructions are well done, although some of the parts may be slightly hard to find. Germanium diodes and high-Z earphones are not as plentiful as they used to be, although you can still find them if you look.

This pizza box rig could be a gateway drug to more serious crystal radios. Or you could go smaller and try building one in a match box.