I am looking for an extremely simple schematics for an AM radio - one tranzistor. To show the radio principle to the kids, no need for exquisite performance.
An (old) Nano to command and an OLED or even LED screen to show the wavelength.
I will use an amplifier module to output to a speaker (this will not be explained :-)).
I search the web but not successful because of overabundance of FM schematics and various radiotransmitters.
I found some very old schematics, but I am not able to find today equivalents for very old diodes, inductances etc.
Not suitable schematics from that search, to many components or no indication of being actually built. My experience with ferite rods is pretty bad, because I was never able to find the same type as the one the author indicates.
I am looking to something similar to Popular Electronics - old Magazines.
It looks like TA 7642 (nowadays variant of ZN414) is the solution and it is available for some 1 USD in my country. It also has a good reputation as part of educational kits.
I even found instructions for a nostalgic DiY replica of a "rocket radio" :-):
I shall give it a try.
A DiY air variable condenser is here:
I am not happy with excessive craftsmanship of this one, but I will re-design it a more functional manner. Or find an alternative.
Still to solve is how to connect to the Arduino, in order to display radio data.
falexandru:
It looks like TA 7642 (nowadays variant of ZN414) is the solution and it is available for some 1 USD in my country. It also has a good reputation as part of educational kits.
I thought of that device of course, but you did ask for 'one transistor AM radio'
It looks like TA 7642 (nowadays variant of ZN414) is the solution and it is available for some 1 USD in my country. It also has a good reputation as part of educational kits.
I am looking for something simple - one transistor seems the first choice. The difficulty is to find feasible schematics for the educational purpose. If not, then I must "blackbox" it (namely - no explanation about electronics, but only generic ones) and attempt another solution.
The ferite rod and the (air) variable capacitor concerns me. Air capacitor is a nice educational solution, because kids can imagine how it works.
One can build a one transistor radio and one can build a radio that displays the tuned frequency. The difficult bit is building a radio that satisfies both requirements because radios that display the tuned frequency are generally using some sort of local oscillator frequency synthesis that uses considerably more than one transistor.
With that said, one could sense the tuning voltage of a circuit like this and it would relate (non-trivially) to some approximation of the tune frequency.
You also could use some transmitters of known frequency and modulation, to show how the variable capacitor is used to tune the radio to a specific frequency.
I am searching for a decently priced AM emitter, not successful so far. On the Diy side, all I foud are real transmitters (they pick voice via microphone).
Doesn't your locality have any AM radio stations left? Those are what you should try to receive for of course.
It's been a few decades since I built my last crystal receiver but I remember all you need is a variable capacitor, a ferrite core inductor (that can double as antenna), a germanium type diode and an earphone. I had one built into a matchbox, just for the fun of it.
No external power needed, that's part of the beauty of the thing. A transistor radio, even a single transistor, does need external power.
falexandru:
Difficult to find Ge diodes. I will visit brick-and-mortar shops - there is one vendor of such grandpa' stuff
That's quite funny as a recent poster proposed (somewhat inappropriately) to use them in a circuit because he had a large quantity very cheaply from an eBay vendor. I think you simply need to know a common type number and search for it.
Oh, come on! You clearly haven't even searched at all!
