Fail of the Week: The Accidental FM Radio

[B Arnold] is hearing voices and needs help from the Hackaday community. But before any of you armchair psychiatrists run off to WebMD, rest assured that [B Arnold] suffers not from schizophrenia but rather has an RF coupling problem.

The project (which isn’t posted yet) is an attempt to turn a C.H.I.P into an Amazon Echo, for which [B Arnold] needed an audio amplifier. Turning to the junk bin, he unearthed an LM386, that venerable power amp chip that first appeared in the mid-70s. Dead simple and able to run off a 9-volt battery, the LM386 that has found its way into thousands of commercial products and countless hacks.

Shortly after applying power to the amp, [B Arnold] started hearing things – faint, far-off voices, scratchy but discernible. A bit of repositioning of wires and hands improved the signal enough for a station ID – an FM talk radio station on 97.1 MHz. [B Arnold] doesn’t mention the call sign, but it might have been KFTK out of St. Louis, Missouri; in any case, it would be helpful to know the range from the transmitter to the inadvertent receiver. Two low-fidelity audio clips are included below for your listening pleasure – you’ll want your headphones on, and Sample 2 is better than Sample 1 – as are photos of the offending circuit.

What do you think is going on here? We’ve heard of RF coupling of AM radio stations before, but how would FM signals be making it into this circuit and out of the speaker? Is there anything [B Arnold] did wrong to get this result? Sound off in the comments and let us know your horror stories of RF coupling.

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LM386 Altoids tin amp

altoids_amp

Hacker [Dino Segovis] is back again with the fifth installment in his “Hack a Week” series. This time around he has put together a 1/2 watt audio amplifier that would make for a great weekend project. He’s a big fan of the LM386 amplifier chip because it does so much in such a small package. Since it is so versatile, he used it as the centerpiece of his Altoids tin amplifier.

Now an audio amp inside an Altoids tin isn’t exactly a new concept, but [Dino] takes the time to discuss the circuit in detail, which is great for any beginners out there who are looking for a fun and relatively easy project. After a high-speed video of the assembly process he walks us through the completed amp, then treats us to a couple of short demos.

One thing that makes his amp different than others we have seen in the past is the addition of a 1/4” guitar jack, which allows him to use his amplifier as a combo amp/distortion effect box.

It’s another job well done, so be sure to keep reading if you’d like to watch the latest Hack a Week episode in its entirety.

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