How About a Propeller FM Transmitter?
erco
Posts: 20,254
A RasPi can do it, how's about a Propeller?
http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter
http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter
Comments
They really don't want to be seen to be encouraging kids to be broadcasting horribly noisy RF signals that could cause interference and get them into trouble with the FCC and such.
-Phil
Since it's clearly impossible for the Propeller, I guess we'll have to settle for the easy, cheesy way out: AM using a crystal oscillator. Heck, even a BS-1 could send tones that way over a short distance to an AM radio.
I bet someone's already done that, could be the start of a nice science fair project.
http://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html
Funny that the frequency range is US-only but from this listing I suspect the instructions are in Chinese!
Edit: Assembled AM/FM Radio under $4!
-Phil
Sounds like one of Beau's "golf challenges". Who can make the "best" transmitter with the fewest/cheapest parts?
I think the pronunciation of that is painsonic. Solder fun yes, but too much pain if it doesn't work after completion. I think I will go with something ready built, surly there is a AM/FM out there for less than ten bucks.
Good luck with that one erco, better brush-up on your Chinese.
Yes, they do not want CE ticks being removed from RaspPi, which some bureaucrat could easily decide to do !!
This comments is interesting :
Modulation is done by adjusting the frequency using the fractional divider between 100.025Mhz and 99.975Mhz, which makes the audio signal. The fractional divider doesn't have enough resolution to produce more than ~6 bit audio, but since the PI is very fast, we can do oversampling to provide about 9.5 bit audio by using 128 subsamples per real audio sample. We were being naieve with our subsampling algorithm - you can now get full 16 bit quality sound, and it even does FM pre-emphasis so that the result doesn't sound bass-heavy.
They may be optimistic with the "full 16 bit quality sound" claim, but the dithering of fractional divide value is interesting.
There must be some slew limit on that & I wonder what the spurs look like on a spectrum here ?
FM is a beautifully simple and open concept. Which is one reason I'm pretty annoyed by the Norwegian government's decision to switch off FM and force everybody over to a computerized, closed, non-standard, power-hungry, incompatible (drive into Norway from Sweden and your car radio won't work) useless digital system. All due to years of lobbying by one particular person inside a department.
We can't even have battery-powered radio clock alarms anymore (unless we want to replace batteries every few days). We're back forty years, in that respect.
Turns out not to be quite so simple: https://en.wikipedia.org/wiki/Countries_using_DAB/DMB
Hadn't really thought about it so hard as I have not felt the need to listen to any broadcast radio since nineteen ninety something.
USA is still all analog! Every radio ever made for here still works fine. DTV was the only digital bandwagon we jumped on in in 2009, and they gave free converters to anyone who asked. New digital TVs are amazingly cheap IMO, but it is unknown how long the cheapies will last.
My 1960 Philco Predicta remains my favorite TV even if they are old school! It was one of the cheapest TVs made back then. (Similar story with the Corvair, is there a pattern here?) But I kinda doubt if anyone will be collecting and restoring today's cheap DTVs fifty years from now.
Then I heard radio broadcasts were going digital. So I thought that was done as well. Seems not.
I did try building a good old AM receiver a few years ago. Turned out there are no AM stations to be heard around here any more.
Total bummer. Crystal radios are magical and a fun, simple way to get kids interested in electronics. As I have mentioned several times, I live about 3 miles from KNX-1070, a 50-kilowatt AM radio station in Los Angeles. I can hear their signal clearly on some PA systems, intercoms, telephones, etc.
And hey Erco, I got my Predicta working pretty well! Horizontal linearity isn't perfect but it still looks great. Been watching Honey West, really fun stuff.
I have DAB radios. They're, well, I can't say it here - family forum - but it starts with c. Lots of 'channels', but radio is not TV - you don't sit there and zap through channels. Nothing is gained, and they're power hungry computers. Sound is bad too - clear, but bad. The electronics is probably so expensive that the vendors have to go cheap on the audio.
FM radios are really easy and cheap to make, sometimes you would get a free (small) one with a magazine. And you can make them yourself, with very little knowledge (transmitters are even easier than receivers). In a crisis situation that would be very good. If everybody have only DAB radios and 1940 happens again, then what? Sorry if you didn't get the reference, but radio was very, very important at that time.
TV is digital. That's fine. It's even a somewhat standard variant. Digital for TV makes a lot of sense, for many reasons. Very few of those reasons apply to radio. (It's even been argued that with DAB you'll be able to see the name of the song played. Huh? FM has had RDS for decades already.)
@jones: What an AWESOME radio and demo! My crystal sets were quick and dirty types with poor selectivity but you can really work the band with yours. Even using a diode instead of a more sensitive and finicky cats whisker. Adding a VFO was genius! Jealous! Did you build that?
That's horrible, building analog radio receivers is a right of passage for every electronics nerd. First you build a crystal set, then a one transistor set, then add another transistor as an amplifier. Repeat until you have a mess of wires.
Plus there's the HD Radio standard that transmits digital and analog in a compatible manner. In the US the FCC has not indicated any intent to shutdown analog radio as it would not result in the recovery of any radio spectrum rights which could be sold.
Kinda funny too that the most sensitive detector for a crystal radio is a cat-whisker detector, which uses a galena crystal, AKA LEAD SULPHIDE. Finnicky to use and potentially toxic to handle, yet pricey and in big demand on Ebay. Between that and leaded solder, the high voltages and hot live-mains chassis often found in televisions and radios, it's a wonder any of us are still alive. Make every day count!
Wow, that ebay crystal set is beautiful.
Now I know what to do with those walnut lumps Chip gave me.
But grief the price. At that rate Chip has a couple of million dollars worth of walnut planks stacked up in his barn.
How about a special edition run of Propeller boards built on walnut frames? Walnut bread boards for the discerning nerd.
I was wondering if it's really true that galena cat's whisker diodes are actually the most sensitive or if that was some kind of audiophile style snake oil. I found this page that actually tries to measure their characteristics. http://www.lessmiths.com/~kjsmith/crystal/dtest.shtml
Looking at the graphs I would guess that a germanium or Schottky diode can be better.
Certainly the OA5 I used in the crystal set I built at age 10 worked well.
Spectrum is valuable, which is what made me wonder if selling off 88MHz to 108MHz for some other use was part of the motivation for the change. Anyway, I'm sorry that's happening. Seems like just the sort of meddling that causes us to be critical of government. It will be interesting to see in 10 years what the Norwegian people think about it.
But why a little country like Norway would go for a totally nonstandard incompatible system, different from the rest of the world, is beyond me.
Somebody must be cashing in on this.
Several years ago I put together a small Amateur Radio Transmitter Beacon for a "fox hunt", using nothing more than a Propeller Board, a 9 volt battery and a very short Antenna (20 inches of wire). My friend, Jeff - ko7m, help with the final design and software. We transmitted on about 10.140 MHz (HF 30m band) using CW signaling.
For the actual hunt, we had 4 different Propeller boards, each were time synchronized and transmitting on slightly different frequencies, each hidden in a different location, each used a different transmitted CW "id" character (F,L, B, V, note: each of these CW characters are the same length).
See:
http://wa0uwh.blogspot.com/search?q=fox+hunt
and,
http://ko7m.blogspot.com/search/label/Fox Hunt
We have used the same beacons for several years with great fun.
But this year, we (actually Jeff) added a simultaneous FM Voice Beacon on about 147.45MHz (VHF 2m band). Note: we used a 2 inch antenna for the FM Beacon.
Check out the above URL's for the Fox Hunt details.
For some of my other Amateur Radion Propeller adventures, see: http://wa0uwh.blogspot.com/search/label/Propeller
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Well, I don't understand Tor's frusteration on the DAB issue here in Norway. I do live in a remote area, far from the cities and populated areas and never been able to receive more then one single FM channel. With DAB I can choose between tens or twenty different channels (also do zapping). But I do prefer the non commercial ones from NRK (Norwegian Broadcasting Corporation).
The audio is really good, especially if I connect the receiver to my vintage Tandberg audio amplifier.
I can't see why DAB radios should be more expensive to make or why they should consume more power, someone has to explain that to me. If we once again experience a 1940 or other bad crises, I don't think the FM will work better then any other systems. In such a case I think we all have to return back to long or short wave transmissions. And lots of people will still keep their good old FM/AM radios even though they usually never use them.
Ok, DAB works pretty good for me, no negative feelings at all.