Building an FM radio from $3 radio chip and an 84MHz ARM Arduino | Hacker News Reader

Building an FM radio from $3 radio chip and an 84MHz ARM Arduino

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69 points9wzYQbTYsAIc30 comments

In 1930-something, my grandfather built a passive radio to use on his family farmhouse without electricity. He ran a wire all the way from the basement (where he happened to get the best signal and for other reasons) all the way to his attic room, and would stay up late all night listening to the radio with his brother. An aside, but this article made me think of this fun little story.

The wire from the basement was for an earth ground, he probably had another antenna wire either in the attic or going outside. Check out Galena detector radios.

Yes, my grandfather did the same thing (a bit earlier, probably late 1910s or early 20s, as he was born in 1908). He used a cyclindrical oatmeal box and wound copper around it to make a tuner. The story was immortalized in a book the Texas Governor's Committee on Again published in the 70s.

https://www.amazon.com/Texas-Sampler-Donna-Bearden-Frucht/dp...

... based on the TEA5767 radio module.

So this is more a lesson in how to wire things together than it is in how FM radio even works.

The TEA5767 is a full FM broadcast receiver on a chip. So yeah, it’s really just how to wire up that chip, connect it to an audio amplifier (LM4811), etc. If you want to learn how radios work, I’d recommend many of the learning materials out there for amateur radio.

To be fair, I'm not sure if you can demodulate a 100MHz FM signal digitally. DSP at this frequency on an Arduino maybe be infeasible (you need a phase locked loop). I suppose if you used a bandpass + low pass filter you can pull it off but that will be a lot more work still.

The enclosure design was interesting - not 3d printed, unfortunately, but still looks remarkably clean.

And the choice of user interface was interesting to see - a single rotary encoder reminiscent of the days of the iPod.

But, yes, definitely more about how to wire together (physically and digitally) the components of a consumer product than about how FM radio chips work or how to build your own radio from crystals, etc.

84MHz? ARM? Talk about over engineering. As the FM receiver IC in this project uses I2C you could do this with an AVR even, such as the 328P, as found in the Arduino Nano. The Arduino Due used here is double the price of the Nano.

People in the US who find this interesting should spend the ~$50 to get licensed for amateur and buy a UV5R radio.

There is just so much one can do and learn with these cheap radios. In many ways, it’s the raspberry pi of radio.

I've heard secondhand mutterings that the amateur radio doesn't like the Baofeng radios due to stomping over other frequencies when in use. Is this just expected internet kvetching, or is there more to it than that? I am interested in learning more, but I don't feel like running in to any more hostility in my hobbies. Genuine question.

It seems like that concern may have been addressed with the more recent releases of this model of radio since March of 2021.

I certainly haven’t experienced spurious emissions first hand. I own a proper Yaesu radio now but the Baofeng is such a value imho for beginners to learn the hobby. One can talk to astronauts on the international space station with one.

They tend to have relatively cheap front ends so put out more harmonic noise when broadcasting. They also tend to be direct conversion rather than superhet, meaning they can be more prone to interference on receive when you have a few of them together.

If you're wanting to get into modern ham radio, then something like an Anytone 878 will do all the analogue as well as digital, which can be fun.

An old WWII veteran who built the on-board CCTV system on a ship in the Pacific once walked me through making an AM radio that worked with no battery — just the power of the radio waves, themselves. Like what today powers RFID chips.

It took him maybe ten minutes of soldering probably six or eight components he pulled out of a box of junk parts.

He grounded the thing by sticking a nail into a wall socket.

It helped that this was in a small town with only a couple of AM signals, so fine-tuning wasn't all that necessary.

You might get a kick out of this: “I bought 1000 meters of wire to settle a physics debate” https://m.youtube.com/watch?v=2Vrhk5OjBP8

AM: https://en.wikipedia.org/wiki/Foxhole_radio

A crystal-set radio was a LOT of people's introduction to electronics, I remember building one with my dad at age 6 or so. We were a fair distance from the station so the signal was faint, but the earphone reproduced enough to hear the news and most importantly, the station call letters.

They really are extremely simple things, and you can use the base-emitter structure in any BJT if you don't have a discrete diode around. The trick is knowing how many turns of wire to put on the inductor, but if you're stuck in a foxhole for who-knows-how-long, you have time for a lot of trial and error.

> Building an FM radio from $3 radio chip and an 84MHz ARM Arduino

The article is great. He just forgot to explain how and why (84 Mhz microcontroller for a FM radio ? ) he did it. /s

Another day, another hack, is the hackaday way.

That in fact is quite overkill; probably it was what he had at hand. That FM chip can be controlled by any uC capable of bitbanging i2c, so pretty much every cheap one including small ATTiny uCs that cost one tenth of the Arduino Due.

Would anyone be able to recommend the most beginner friendly “assume (almost) no knowledge” of how to implement an fm radio using 1) a dsp “pipeline” 2) analog electronics?

If I wanted to understand every single step of the dsp process and what each individual piece of electronics did in “decoding” a fm signal, where should I turn to?

Thank you!

FM radio receivers were a staple of those electronic kits I used to play with as a kid. Here's what a quick Google search shows: https://www.electronicsforu.com/electronics-projects/simple-...

The difference in complexity between this and something commercial are extras like decoding the stereo subcarrier and applying the data to the main signal: https://en.wikipedia.org/wiki/FM_broadcasting#Stereo_FM

Yeah, I also did electronic kits as a kid, and both learned how to read a diagram thanks to them, but never understood what individual parts did in any circuit.

I “get” I=V/R (I mean not really… I know it exists), but how to go from there to understanding what each capacitor is doing in the simplest of fm circuits?

Is each component doing the equivalent of non-trivial real-time signal processing? How to visualize / think about it?

I’ve mentioned this on another sibling comment, but amateur radio is where you need to look. It took me about 6 months of casual study to go through all three license classes (tech took me like 2 weeks), and you learn quite a bit about everything you’ve mentioned in the process. More than that, you gain a license which allows you to legally experiment with this stuff.

Original version mentioned in this blog/video. https://www.changpuak.ch/electronics/Arduino-Shield-WACHARA1...

Didn’t RPI have In built capability to do that? I built a cheap streaming system, back when bluetooth wasn’t so main stream to make “piplay” for my stereo in car with Pi2.

I’m not sure, it might.

As I recall, some ARM SoC have FM radios in them.

edit: ah, it was the Qualcomm modems that I was recalling

https://www.wired.com/2016/07/phones-fm-chips-radio-smartpho...

Sort of. The Raspberry Pi CPU had a configurable clock generator that could output up to about 125MHz to a GPIO line. Some people figured out that it was possible to rapidly change the configuration registers to modulate an audio signal onto a carrier frequency in the FM broadcast range. [0] So you could make a low power FM transmitter using just a Raspberry Pi and a piece of wire.

[0] http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspb...

You can also make a shortwave receiver in a similar way with a SI473x chip. It's a bit more expensive, but it can demodulate also SSB.

and for my next trick I'm going to make a slingshot with only two parts: a slingshot and a squirrel

Hah, neat trick!

https://allanimalsfaq.com/squirrel/how-to-make-a-squirrel-sl...

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