My MIL is 93, and the only tech she can really deal with is turning on the radio and TV and changing channels.
She is fond of music from old classics (from the 60's and earlier), so I hooked up a Raspberry PI with an FM transmitter and created her own private radio station. She tells me what songs she likes and I create different playlists that get broadcast on her station. It preserves the surprise element of radio, and there is nothing in there she doesn't like.
The tiny FM transmitter is surprisingly powerful. Her neighbours (of similar vintage) are very happy too, so their requests have also started coming in :)
EDIT: I wanted to add that I am the UI ... she doesn't get to choose the playlist. To make my life easier, I just created different playlists for different times of the day ... calm/spiritual/slower numbers in the early and late hours, peppy during the late morning and evening etc.
You should know this is heinously irresponsible and very illegal unless you apply proper filtering. Bashing the GPIO pin adds a ton of harmonics that fall outside the broadcast band, up into aircraft and military and who-knows-what other frequencies.
The README goes over this, but if people keep blindly ignoring it, expect regulators to figure out a way to make our lives a lot less fun.
Unfortunately that's not that simple. Your observation may well be the case, but that has nothing to do with whether it's going to interfere with someone else. Here's why:
(tl;dr: The output of these "transmitters" contains spurs you're not equipped to detect but which can indeed be problematic for others. Transmitters are regulated for sound physical reasons, some which are enumerated here.)
The range at which your FM receiver can pick up an FM signal may indeed be ten feet, but that's a product of the transmitter power, the transmit antenna gain, the path loss, the receive antenna gain, and the receiver sensitivity. To infer anything about one of those parameters (for this discussion, the transmit power), you have to know the other four, and you don't. (And neither do I. Even the measurements I'm equipped to make require a lot of assumptions and have significant uncertainty.)
Secondly, FM (radio folks would call this wide-FM) is particularly power-hungry because it occupies a relatively wide swath of bandwidth. Typically limited to 75kHz and in practice somewhere around 50 for analog stereo or just shy of 60 with RDS (which pifmrds can do). For example, a 104.3MHz station is actually transmitting anywhere between 104.225 and 104.375 at any given instant. This means that the receiver has to demodulate the carrier which may be varying all over that range, and it requires a fairly strong signal to do that. If the FM receiver loses lock, it doesn't mean the signal doesn't exist, merely that it's below the receiver's sensitivity.
Other spectrum users, like radar for example, may be dramatically more sensitive, and pick up a signal of the same strength many miles away. A mode that occupies less spectrum generally requires less power. They may also have better antennas (radar dishes tend to be tightly focused, that's the whole point), better receivers (local self-noise can be minimized through careful-but-costly engineering), et cetera.
They may also be above you, so while you see the signal disappearing as soon as you get on the other side of some hedges, there's no foliage between you and an airplane.
So while _for you_, the effective range may be ten feet, but for someone else, the signal may be a problem dozens of miles away.
Furthermore, and the whole point here, is that you're not just interfering with other users in the 88-108MHz FM broadcast band. (If you were, frankly, I wouldn't care one bit; there's little actual harm to be done.) It's that as a digital pin being bashed up and down at those frequencies, the resulting signal is profoundly not sinusoidal. It has much faster rising and falling edges, which mean the signal has plenty of energy in harmonics, not just the fundamental frequency of the carrier. My spectrum analyzer only goes to 2.7GHz and I was able to see (admittedly diminishing) energy up beyond 1GHz, which is both impressive in that the BCM chip's GPIOs can slew that fast, and terrible in that you're interfering with _everyone_ when you do it.
So, say you've told pifm to transmit at 88MHz, right at the bottom of the broadcast band where off-the-shelf receivers can pick it up. Your little Pi and random-wire antenna are also producing quite a bit of energy at 176Mhz (maritime VHF ship-to-shore and stuff), 264MHz (military air-band, adjacent to a satellite-earth-station band), 352MHz (more military), 440MHz (amateur UHF), etc. All the way up.
This may be counterintuitive, but that's why radio is governed by regulations rather than YOLO, and why even unlicensed toy transmitters still have to comply with harmonic-content rules.
Filter your Pi to knock out all those harmonics, and the odds of the Coast Guard or Air Force knocking on your door will plummet.
(Also, I've measured the power coming out of one of these things, and if you can only pick it up ten feet away, either your antenna is total crap, your receiver is deaf as a post, or both. Even after applying proper filtering which eats some power, I was able to receive mine on a pocket radio out to about 200 feet, which surprised the heck out of me and I added lots more attenuation until my most sensitive receiver could no longer see it at the property line. It's a fantastic toy for exercising RDS/RBDS receiver and parser code, but it requires a little care and knowledge to use it responsibly.)
Anyone can learn this stuff, and everyone should, especially if they're going to put it on the air.
I am absolutely LOVING Volumio. It's running in a VM in my garage computer that does various other things. At the time, Volumio didn't have a clean way to do this so I just hacked away until it booted and played music.
A little USB sound card is passed through to the VM and it's been rock solid for about 2 years now. I use it exclusively as a Spotify chromecast type thing that cost me about $3.50 in parts.
A standard 3.3V GPIO can typically push something like 30 to 60 mW. You won’t get all of that as transmitted signal — it will depend on how well your random antenna wire matches the impedance of the gpio and the frequency. I’m really not sure the audio quality is going to be anything more than just intelligible, but I’d guess you’d get at least 10 mW or so of useful power, which means it should generally work within a small house.
For the true feeling of radio, you might throw some episodes of The Big Broadcast on there as well - I believe archive.org has some but they're easily findable elsewhere. Donate some money to WFUV[1] or buy some of the collections[2] if you just want the music.
> The tiny FM transmitter is surprisingly powerful. Her neighbours (of similar vintage) are very happy too, so their requests have also started coming in :)
Sounds like you're about to start a Radio station for the nation.
Based on how you're asking I assuming that "Radio station for the nation" is a quote from a movie or something, but searching for it reveals surprisingly little (and is surprisingly random - Google / Bing clearly has _no_ idea what I'm looking for :) )
Is this a quote / reference to something? If so, could you let us all in on what it's referring to?
OP seems from India and AFAIK its illegal to transmit on FM frequencies without a license. I understand it might be low powered but theres a chance of Police coming knocking on the door. Whats worse is it might interfere with emergency services. There is a reason we have spoctrum licences.
I know. It is illegal in most parts of the world. I'm taking over a commercial FM channel that my MIL won't listen to, and the transmitter has about a 20m radius.
If the police come, I'll use the Constanza "Was that wrong?" defence.
... I've always been amazed how often "Was that wrong?" works.
I guess I shouldn't be. Even letting them know you were fully aware you were breaking the law, most people would see its intended purpose -- to bring a little peace and comfort to a very old woman -- and have their own compassion kick in.
YMMV but I'm guessing you'd hear something along the lines of "Oh,... well,... (shuffles feet) ... just turn it off, then". Many of us have elderly people in our lives we wish we could provide some comfort to and most of us know we're headed there (if we're lucky to live that long). You know, assuming your 20m radius FM transmitter didn't, say, cause some cataclysmic event/knock emergency services offline for several city blocks, etc.
Put another way, while some police actually will pull you over and write you a ticket for going a couple of miles (km) per hour over the speed limit, most won't waste the brain power/physical energy/thermal paper to bother enforcing it.
Well put. Exactly my thoughts. And given my MIL's attitude towards any visitor, the cops will be plied with food and chai till they burst. They will forget what they came for :)
> I've always been amazed how often "Was that wrong?" works.
This is in line with Peelian principles of policing. It was explained to me by a policeman and it was fascinating. He had worked in the UK, Australia and New Zealand.
In his view, Australia was considerably harsher in its policing and NZ was at the other end of the spectrum, UK in the middle.
I’ve had much better luck with 100% honesty. Just say you set up a 20m transmitter to improve the life of a 93 year old woman.
I bought a house in my very early 20s. Roommates of mine finished the third floor with no permits. Went to sell the house ten years later and the location it was in required a U&O inspection. My realtor told me to lie, apply for a permit and pretend I just did the work.
Instead I called the local building inspector and said, “Hello my name is xxx and I’m calling to confess.” He cracked up laughing, came to the house immediately to look at everything and told me I was fine.
Yeah no one will bother with such a low-powered device. I used an in-car bluetooth-to-FM tranmitter bought from Amazon India for years. They've been sold openly since forever. Like this one: https://www.amazon.in/Portronics-AUTO-10-Bluetooth-Car/dp/B0...
Ha ha, I must have pulled up along side you the other day.
Just kidding, I'm in the U.S. But more than a few times I have suddenly got Mexican musical content on my radio in the car when passing close to another car.
I love these things, it's so simple and it's often a better UX than any car bluetooth provides. You also used to be able to buy aux adapters that went in your cassette deck!
I hope they don't know how to use Google and if they do that that is a pseudonym you're posting under here or you might be in bigger trouble than you started with ;)
Anyway, cool to see you hack this, maybe try to tweak the power levels a bit so the neighbors don't have a reason to talk about it.
The FCC allows personal FM transmitters to operate with a maximum power output of 250 microvolts per meter at a distance of 3 meters.
Other countries are more permissive, so this is not a problem. As long as you don't interfere with anyone and emit in a band that's not used in the area, it's perfectly fine.
Makes sense. I’ve seen Bluetooth fm dongles for cars to this effect. The dongle connects to your phone on Bluetooth and the old car can listen to your Spotify via the radio.
I was curious what kind of range that might have, so I put what you said into chatgpt and asked what the range of a typical car or home stereo would be, and it gave me this (not sure if it's correct). FWIW, much less than 20 miles, haha.
--
The maximum power output of a personal FM transmitter allowed by the FCC is 250 microvolts per meter at a distance of 3 meters. The range of the transmitter depends on various factors such as terrain, obstructions, and interference.
Assuming ideal conditions, such as no obstructions or interference, the range of the transmitter can be calculated using the inverse square law. This law states that the strength of a signal decreases with the square of the distance from the source.
At a distance of 3 meters, the signal strength would be 250 microvolts per meter. At a distance of 6 meters, the signal strength would be 62.5 microvolts per meter (250/4). At a distance of 9 meters, the signal strength would be 27.8 microvolts per meter (250/9).
Typical car and household stereos have a sensitivity of about 2 microvolts per meter. Using this sensitivity value, we can calculate the range of the transmitter for these devices.
For a car stereo, the transmitter would have a range of about 26 meters (square root of 250/2). For a household stereo, the transmitter would have a range of about 63 meters (square root of 250/0.5).
However, in reality, the actual range of the transmitter may be shorter due to various factors such as interference and obstructions.
Where I live, this is absolutely not the jaywalking of RF violations. In Germany, if it is proven that your signal was potentially interfering with emergency services, you will be liable for any damage to victims in civil courts. And if somebody dies in your area because the emergency services couldn't get there on time, you will be criminally charged for "negligent manslaughter."
I wouldn't play at all with non-approved RF frequencies personally.
It literally took a single google search to find out that you’re wrong.
FM transmitting for private use is completely legal for UKW frequencies between 87.5 and 105 MHz and transmission powers lower than 50nW [1]. You can buy perfectly FM transmitters for your car, etch
In Germany (like afaik all the EU), you can also freely buy and use small low-power FM transmitters for exactly the use case of sending your own music to radios...
If a low power FM transmitter on commercial frequencies can interfere with your emergency services, you may have bigger problems. IIRC they have their own specific frequencies.
In germany its also legal to use plenty of bands in the RF Spectrcum with up to 750Watts (and potential more).
We are also allowed to do CB Funk in Channels 1-40 without anything and up to 80/85 (forgot details) when you register with Germany.
So your statement reads more like you are not allowed to do anything in germany. Its hard to believe to disturb stable systems just because someone is doing a little bit of FM on some known frequencies.
What would happen if you delayed an ambulance responding to an emergency by jaywalking in front of it? Could you be charged if someone died as a result?
In Switzerland they can (and often will) at least fine you if you neglect to dirve to the side when encountering traffic on a highway (to form a "Rettungsgasse"[0]) to allow emergency cars to pass in the middle.
As someone who's worked in telecom for a number of years, the fines for broadcasting I've seen issued to individuals are insane. Not just radio but wireless amplification too. Different European country though.
Always check the legislation in the country of operation. Emergency frequencies are held sacred by the powers that be.
Yes, technically it is illegal. But I've seen all kinds of gizmos that would inject a signal into the FM band to allow the use of car stereos that didn't have an 'aux' input. At those power levels the FCC isn't going to be bothered unless someone lodges a complaint, and even then they'll have a hard time finding the source unless they're practically standing on top of it. OP may want to turn down the radiated power until it just works for his MIL but no longer for the neighbors.
Oh how many phrases start "Yes, technically" in my life.
The law is an interesting beast. I know nothing about the law in India as it relates to FM band transmitters but I suspect that the law predates the common availability of adapters that one might use in ones car to add an input to a stereo that lacks such a highly technical circular hole for such purposes[0]. Once these devices gained wide adoption due to both their utility and -- more generally -- the fact that operating one is usually so benign that they can be difficult to discover let alone actually cause enough interference to warrant them to be seized.
The intention of the law was to prevent someone from operating a pirate radio station/give exclusivity to a single license-holder for that frequency. Since these devices don't violate the spirit of the law, the governing body finds it easier to carve out an informal exemption rather than explicitly write one in. It can also be tricky to correct a law that has a very valid reason for existing but may have cases where total enforcement isn't realistic[1].
The law may not have caught up to the reality on the ground and the legislatures answer to it is "enforce it when the interference is enough that someone notices." One might imagine a world where something akin to TV Detector-like Vans[2] drape the country-side in a dragnet to catch all of those pirate FM-input-devices but that usually only happens if there's a substantial amount of tax revenue to be gained ... to pay for the vans.
[0] I had one of these in the 90s (in the US, where it's not illegal if designed correctly) that connected my Discman to my ridiculously sad factory radio which lacked both external input and even a cassette deck.
[1] I do very little with regard to radio communication (if that isn't obvious) but I'd imagine most lawmakers do even less, so now you have to bring in experts to figure out "what's an acceptable amount of interference in this specific use case" and "how should a device like this be restricted." Not that government isn't famous for wildly wasting money or anything but I'd imagine the thinking is that it's not worth the effort to correct.
[0] I had one of these in the 90s (in the US, where it's not illegal if designed correctly) that connected my Discman to my ridiculously sad factory radio which lacked both external input and even a cassette deck.
Heh. I drive a 2002 Chevy Suburban (don't laugh, I have a strong aversion to spending money on new vehicles) and it lacks an AUX input, so to this day I use one of those low-power FM transmitter adapters to pipe my phone's audio output to the vehicle stereo. They are amazingly handy little gadgets.
That just wires the speaker output of the device to a set of coils sitting right in front of the tape playback head. GP did an end run around that by wiring straight into the trace in between the head pre-amp and the main amp.
But quaintdev is right in that Indian Police for some reason takes this somewhat seriously. For highway patrol, I suspect it's boredom and this gives them something to chase. I remember in the late 90s when I was in college, the police showed up a couple of times when students were transmitting from one of the hostels. They'd let it go, but they did show up.
I suspect the OPs transmitter is hard to detect even at close (< 100 meters > 30 meters) range. Anything more powerful and you would definitely attract attention.
If we ever have a world apocalypse and I’m alone, I know I can at least conjure one companion by suggesting I would use spectrum without a license and a ham enthusiast will appear.
<Dusts off Ham Licence> Anyone can use amateur frequencies in a genuine “no other communication options available” emergency, if I remember the regulations correctly.
Edit: “§ 97.403 Safety of life and protection of property. No provision of these rules prevents the use by an amateur station of any means of radio communication at its disposal to provide essential communication needs in connection with the immediate safety of human life and immediate protection of property when normal communication systems are not available.”
Illegal in India maybe. In the US: "In the United States, Part 15 of the U.S. Federal Communications Commission rules specifies that no license is needed if range of the transmitter does not exceed 200 feet (61 meters), although the Part 15 rules specify that the field strength should not exceed 250 µV/m (48db) at 3 meters"
I haven't found the exact law in India, but looks like maybe it's legal for personal usage of FM provided power of transmitter is under 500 mW?
Worth noting that there already exists a product in the Indian market by a big music label that addresses this exact issue. I’ve bought my grandfather one of those and he’s very happy with it!
Do you mean the saregama Caravaan? If so, I bought her one of those and it just didn't cut the mustard.
The built-in collection either didn't have songs that she liked (from the '40s), or they weren't clustered together, or were mixed up with other songs.
I could load a flash disk with her playlist to plug into that player, but it wouldn't know what to play at what time (calm songs in the early and late hours, peppier numbers on other days, festival specific numbers on some days). This was a big deal. I can even change the playlist from elsewhere (a script automatically mirrors the playlist that I maintain on a server)
Bluetooth streaming is possible with the device, but not an option for my MIL ... that would require her to learn to use a cellphone.
I don't know if you are from India but our laws are so complicated that I am sure every moment we are breaking one or the other. If we constantly worried about which ones we are breaking we would never get anything done!
The internet archive has tons of old radio shows too; my favourite is The Adventures of Sherlock Holmes, which aired in the early 40s. Best thing is that it also has the original ads in there. “Now that the poultry shortage is over, why not enjoy a glass of wine with your Sunday chicken roast?”
Might be cute to include some old original programming in your pirate radio!
Would love to see a blog about this setup. I, not old, always want to dump much of my music & simply want to listen whatever is next (& miss it if I don't listen) just like radio.
Have you seen Icecast [1]? You create playlists of local music, then play them with something like mpd. Icecast then streams them out and clients like VLC, xmms2, and even older versions of Winamp can stream it.
I set this up for all my music in shuffle mode for my own radio-like always on streaming service via Tailscale.
I’ve wanted to try something like this with a Pi or something else running Linux. Is mpd a good choice for that scenario? Does it support being able to use custom events eg a button on the gpio for play/pause?
mpd is a great choice, there are lots of things built around it. Essentially, you'd have the GPIOs trigger mpc commands. mpc talks MPD over the network back to the mpd server, so you could have physical controls all around the place.
I used to work construction with one of those big old radios covered in paint that has been dropped 1000 times--we got around to using an FM transmitter dangling off the phone for it. It was fun + charming, since then I've thought about getting a big radio setup and hard-wiring Bluetooth in but your setup sounds truer to the concept.
FWIW there are many transmitters similar to what they built that enable playing MP3 players, phones and other things on old radios [1]. I do not remember what the power limit is but no permit is required. They can operate throughout the entire FM broadcast spectrum. If they are broadcasting good music in an elderly community I doubt anyone will complain.
Several homes in my city put up holiday lights that are synced to music and transmitted over FM. The signal only works if you’re parked near the house.
From my MP3 collection. I buy the songs or albums she likes and broadcast them. For some that are not on sale anywhere, I scrape them off youtube, but usually send a note to that channel for original sources where I can pay for it.
Cool! I asked because there are many niche playlists on Spotify you can find for oldies, for example some very specific for the 60s, 50s, 40s, etc. Perhaps it could help her discover similar, but new, music.
They all sound out of breath. Not sure what causes that effect/perception. Listening to it again, it seems like the plosives (like d, or t) have no pop like there was no air pressure behind them.
I forget. But just search for "kit FM transmitter". I'd fully intended to build a "proper" transmitter, and was keenly disappointed that you could just buy a cheap single-chip board.
Nowadays you don't even need that. You can turn the RPi itself into an FM transmitter. Search "how to FM broadcast on raspberry pi"
> You can turn the RPi itself into an FM transmitter.
Never tried it, but given the way it works, you definitely need some output filtering unless you accept to pollute all harmonics of your channel (which might be licensed spectrum too, and interfere with services you don't want to interfere with in the first point)
Pico caps and appropriate impedance miss-match can be used to round-off square waves.
But yes, if you look at high-speed Pi GPIO with a Rigol it looks more like an EKG readout than the thing you might see on a logic analyser. Smoothing it enough to feed a line-amp is very lossy.
Pi for audio frequencies is lovely and square, Pi at radio frequencies has distinct rise and fall and "just taking a moment to think about it" segments.
A spectrum analyser has probes!?!? This might be where I am going wrong... But the bench scope is largely in agreement about the distinct phases of a cycle at RF freq.
One can go on Amazon and order himself a high powered FM transmitter direct from China. Stick an antenna in the attic and you'll be heard for miles. If you don't gaf about spurious emissions or laws or anything like that you too can be Christian Slater in Pump Up the Volume. The fines for this in the US can be pretty severe but Amazon is happy to sell you the rope to hang yourself with free shipping.
She is fond of music from old classics (from the 60's and earlier), so I hooked up a Raspberry PI with an FM transmitter and created her own private radio station. She tells me what songs she likes and I create different playlists that get broadcast on her station. It preserves the surprise element of radio, and there is nothing in there she doesn't like.
The tiny FM transmitter is surprisingly powerful. Her neighbours (of similar vintage) are very happy too, so their requests have also started coming in :)
EDIT: I wanted to add that I am the UI ... she doesn't get to choose the playlist. To make my life easier, I just created different playlists for different times of the day ... calm/spiritual/slower numbers in the early and late hours, peppy during the late morning and evening etc.