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.
A capacitor across the piezo might help boost the amplitude a little by following the envelope a little more closely.
No diode, you need a galena crystal and a cat’s whisker. (Look ’em up, kiddies :-)
If you watch the whole video he does show the old blue-razor-and-pencil trick.
Also, the suspense of the third paragraph above is killing me….
But dose the video include using a lantern flame as a high impedance speaker if there is no crystal radio earphone laying around in your foxhole? I understand that an older wireline telephone ear-speaker will work too. This was the difficulty with crystal radio in the 90s, finding a high impedance earphone once Radio Shack dropped them.
If you know how to use a lantern flame as a high impedance speaker, you should definitely make a video or something. That sounds fascinating.
You have to retune galena often. Not very fun. A cheap diode from a Goodwill radio is way better.
There is no way… that I would ever have come up with this idea.
No mention of diode used… probably a 1N34. If so you can supercharge operation by using a 1N60p. MUCH better sensitivity (lower junction voltage.)
Now the big problem: finding an AM station (or any current broadcast station) worth listening to!
1N60P Hah! Buy online – you never know what you’ll get. Most are Schottky Si. Same warning (with a bit less emphasis) for 1N34A.
Just avoid those 1N34s sold from Chinese vendors off Ebay as they’re all fakes, especially those labeled as DO-35 cased (most legit germanium diodes are in case DO-7).
Nobody makes GE diodes anymore, so either one goes for Schottky diodes or buys GE ones from reliable sources. Most sellers from eastern Europe offer GE diodes at low prices, including military grade soviet ones.
Nicely done. Back in our day we used a rusty old razor blade for the detector! :D
Oh that’s super cool. I’m going to print this.
A fine stuff and explanation. A little more on the detail of coil winding would be very helpful to me.
Nice article. Brought back memories of making crystal sets back in the early 60’s. I wound my own coils using the cardboard tubes from the insides of toilet rolls, and variable capacitors from salvaged radios. My final set had a 3 gang capacitor with a step down gear and a nice big knob and dial all mounted on a piece of wood. The aerial was about 160 feet of 16 gauge wire strung over the top of laundry line poles in the back yard of our apartment block in Glasgow! I could listen to the BBC’s cricket commentary on this one or the pirate radio stations in the North Sea. Great fun.
I agree this would make a wonderful kit for classroom experiments.
don’t forget that you can make the headphone speaker out of a buzzer ( and you can cut a pen for directing the sound out of the hole )
A buzzer??
Landline phone/handsets also have nice speakers on them.
There are certain technologies that are incredibly inefficient that you hope never go away just because of the magic they can instill. The first time you hear real music coming out of a crystal radio is one of these – bonus if you can do it with a big band station. Watching a real picture come up out of a formerly blank sheet of paper in a tank of chemicals is another.
Everyone should build a crystal radio at least once.
Is it possible to use this circuit (or similar, i.e. with smaller coil) to receive FM? I read about a simple FM receiver (but more complex than this) which uses the fact that received spectrum’s peak has non-zero width – it’s slopes are linear in some ranges. If resonance frequency is slightly detuned from wave’s main frequency, FM causes changes of resonator’s current.
But I thought that it may require a variable capacitor – such a regulated coil doesn’t allow very precise regulation as it can only switch between another windings. But making a varicap if you don’t have one isn’t so hard. There are also coils with core that can be moved partially in or out.