Propeller Broadcast Communication
Humanoido
Posts: 5,770
Is this possible - to do serial wireless communications using only the chip?
humanoido
humanoido
Comments
If so you could build a tank circuit and radiate the energy in an antenna. A similar circuit will work as a receiver. If you use just wire as the antenna, the higher the frequency the shorter the wire. 433Mhz is 23cm for a 1/4 wave. 43Mhz is 230 cm. 4.3Mhz is 23 metres. Somewhere in there will be a value that will work. But it will have to be in a free band and that might be the biggest issue. You can't just pick a random frequency.
Of course, if we are allowed more components, eg a ferrite bar, inductors for tuning antennas so they can be shorter, a transistor or two for amplification, a yagi antenna then it makes things even easier.
This is a fascinating topic. I have done a number of experiments over the years. First issue I think would be to find a suitable band, especially legal bands for non hams. There have been discussions on this at the picaxe forum - the problem is that most frequencies are spoken for. 40Mhz and 27Mhz are the radio controlled people and if you suggest those then someone will (rightly) point out whether you want to be responsible for a plane crashing into somones house. 40 to 88 Mhz includes a lot of emergency services, some TV channels and the like. The old 27Mhz CB band isn't used much but only voice is allowed there. I think there is a ham band at 10Mhz. I've pondered using a band just above the AM radio band but you can get problems there too - eg 1W can get you thousands of miles so even the legal 10mw is a problem. Plus the antennas start to become wires that go round and round your backyard. There are 'FM bugs' that transmit in the 88 to 107Mhz FM band but I think that is beyond the propeller. And the 433Mhz band for garage door openers is way beyond the propeller.
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www.smarthome.viviti.com/propeller
Post Edited (Dr_Acula) : 3/17/2010 6:30:52 AM GMT
humanoido
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Leon Heller
Amateur radio callsign: G1HSM
humanoido
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Style and grace : Nil point
Yea, after all, waves travel infinite distances, through everything, lol.
Yes, everyone should learn about RF before transmitting. (which includes laws, plus radiation limits)
We should all be encouraged to learn the technology that creates these "illegal" mysterious "aether"
A better approach is educate people on what situations cause these various waves.
I found that using certain simple circuits,with pcb traces, and ONLY the prop, one could disrupt other various types of waves fairly easily and at a surprising distance.
With my copy of Viewport, I can now look at various pins (plus combinations) and if I understood what generates what, I might be able to actually avoid circuits that tend to cause EMI.
But because its taboo and illegal, i'll never know that my simple circuit is KILLING the station 93.7 fm for a few miles x ¶.
5pie5
Put two or three near a rusty bolt and pick a frequency, any frequency....
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Style and grace : Nil point
Jonathan
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lonesock
Piranha are people too.
the application area is the key... how far do you want to communicate? Are your Props in fixed relationships to each other?
For lots of application areas, broadcast doesn't necessarily limit you to radiated radio signals. You can radiate visible light or infra-red for pennies. As long as you can look at it without blinding yourself, no-one is going to complain too much. The flourescent light bulb above my head is modulated. I can see modulation of the light with the TSL1401. There is no law that I know of about using moduated light sources to communicate.
Low power rf is only predictable for effects on hardware, when you look at bio-effects, there is evidence that power is really not the only issue. Modulation and relationships to ground fields are what seem to matter.
One of the drawbacks of working in this field is the risk of all kinds of chronic and metastatic diseases. There are no reasonable guidelines. Power and frequencies can be regulated, but that is about it.
And the problem doesn't get discussed very well. Given a choice between solving a problem with light and solving it with radio, light would seem to be the way to go. Some problems can't be solved that way... and the benefits of communications seem to vastly outweigh the inherent risks... but when you are adding to a thoroughly saturated RF environment, you should have a really good reason for doing so.
I once hired a kid who was using RF to give his mother headaches.... literally. He didn't do much for me... but his mother got some relief[noparse]:)[/noparse]
Rich
the application area is the key... how far do you want to communicate? Are your Props in fixed relationships to each other?
For lots of application areas, broadcast doesn't necessarily limit you to radiated radio signals. You can radiate visible light or infra-red for pennies. As long as you can look at it without blinding yourself, no-one is going to complain too much. The flourescent light bulb above my head is modulated. I can see modulation of the light with the TSL1401. There is no law that I know of about using moduated light sources to communicate.
Low power rf is only predictable for effects on hardware, when you look at bio-effects, there is evidence that power is really not the only issue. Modulation and relationships to ground fields are what seem to matter.
One of the drawbacks of working in this field is the risk of all kinds of chronic and metastatic diseases. There are no reasonable guidelines. Power and frequencies can be regulated, but that is about it.
And the problem doesn't get discussed very well. Given a choice between solving a problem with light and solving it with radio, light would seem to be the way to go. Some problems can't be solved that way... and the benefits of communications seem to vastly outweigh the inherent risks... but when you are adding to a thoroughly saturated RF environment, you should have a really good reason for doing so.
I once hired a kid who was using RF to give his mother headaches.... literally. He didn't do much for me... but his mother got some relief[noparse]:)[/noparse]
Rich
Within an enclosed area a beacon, or a set of beacons, could be setup.
I too have (allegedly) used RF to annoy a waste of oxygen. The wastrel would sleep all day, get up at about 19:00 go and get drink and drugs, and at 01:00 thought it was his right to start woodwork.
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Style and grace : Nil point
humanoido
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Leon Heller
Amateur radio callsign: G1HSM
humanoido
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Leon Heller
Amateur radio callsign: G1HSM
Post Edited (Leon) : 3/18/2010 12:59:25 PM GMT
I've got a number of 433Mhz modules connected to propeller chips and all happily communicating. I just picked up a couple more for $15 each on ebay. Legal power, over a kilometre of range and legal RF band. Maybe there is a faster/smaller/cheaper way to do this with a propeller talking directly to an antenna but I'm not sure I can see what it is.
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www.smarthome.viviti.com/propeller
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Style and grace : Nil point
-Phil
Phil - "And that was before Hertz and Marconi came along. Bell was way ahead of his time!"
I knew it! We're merely reinventing the wheel, over and over again!
Ever feel like we are "spinning" our wheels? [noparse]:)[/noparse]
Dr_Acula - "That is the length of the arms of the yagi and it can't be miniaturized unless you want to sacrifice a huge amount of db loss. Ok, you can tune antennas to some extent with loading coils and yes, a ferrite works for your AM radio, and yes, there are clever things like loop antennas, but all of these are compromises."
That's the idea, to sacrifice a lot of db loss, and compromise because the range cannot exceed 1.5 or 2.5 meters.
humanoido
-Phil
Ok, so let's adjust the signal so that it becomes significantly weak beyond the 2 meter limit based on a grounded bubble grid shielding.
humanoido
I'm still laughing because I don't think he is joking. This is the bizarre world of RF.
In moments when I really want to challenge my brain, I look up the Aether and the Michelson-Morley experiment. I wish I could understand Maxwell's equations, and I know that the MM experiment paved the way for Einstein, but in moments of lucidness I still have doubts that the MM experiment truly did disprove the aether. There is something about Lorenz Contraction of the experimental apparatus itself that I can't quite grasp.
In any case, I think the aether is still useful as a way to understand RF. Maybe it is not the real model, but it leads to conclusions that are still useful. Take a length of wire. Oscillate it with a sine wave. At most frequencies, it just oscillates. But at a certain freqency, V=f lambda, the energy disappears. It just is gone. We call it electromagnetic radiation and there is an electrical component and a magnetic component. I'll come back to that in a bit because the magnetic component might be relevant here.
Where does this energy go? EM radiation is a wave, like a wave on the sea. It bends, it reflects, it interferes, just like a wave on water. But what is the 'medium' through which EM radiation travels? The aether? We threw out the aether a hundred years ago but have we yet to replace it with a better model? What is a photon? A tiny particle of light? Not so, a photon can be any size depending on its frequency. A photon of 433Mhz radiation is 68cm long, and you could hold it between outstretched arms. It can travel across the universe unimpeded, so the universe must be 'clear' rather than 'opaque'. Everything about quantum mechanics suggests that this is a wave, not a particle (except the fact that it travels without being impeded). It interferes with other waves, it reflects etc. As the physicists of the 19th century argued, surely it must be travelling through some sort of medium.
Let's create some of these 433Mhz photons and send the electrical component through the aether as well as the magnetic component. We create them with a wire oscillating at the right frequency. We detect them with a length of wire of the same length. We can concentrate them with a parabolic reflector.
But what is going on with a yagi? We detect the wave coming straight at the yagi, but a yagi behaves as if it collects from a much wider area. The first element of a yagi not only detects the wave, but it slightly bends nearby waves so they now are bent towards the yagi and are detected by the second element. And that second element bends nearby waves so they fall on the third element. What on earth is going on here? Is there another explanation, another model?
Ok, so what about the photons a propeller can create? 80Mhz, 3.68 metres long, 1/4 wave=92cm. We take a length of wire that long and oscillate it and the photons and the energy just disappears off into the aether. Sure, a smaller wire will also do that to some extent but a lot more energy disappears if the antenna is tuned.
Can we get that energy back? You bet, just with another length of wire. But the challenge here was to make it small, so let's sacrifice the electrical component of the photon and just go for the magnetic component. Now we can wrap a wire round a ferrite core and generate the magnetic part of a photon, and detect it nearby with the same apparatus. I know this probably is not legal, but my CRO only works to 10Mhz so pick a frequency lower than that so you can see what is going on. Go for a frequency just above the AM radio band - 1.6mhz. Longer photons, much longer, but we can cheat and use a standard ferrite antenna out of an AM radio. Build a tank circuit out of a C and an L and oscillate it at this frequency. Magically make the energy disappear into the aether by connecting a tuned antenna - ie the ferrite antenna. Use the magnetic component of the electromagnetic field. Detect it nearby with another ferrite antenna. Use AM modulation and good old-fashioned crystal radio technology with a detector diode. Use the Bell modem object in the obex and modulate that at audio freqencies, and it should be possible to send information over short distances. I think we are talking less than ten components here and they are all available for a few dollars at electronics stores.
RePhiPi "they can roam as far afield as they want. They just get a little weaker, the farther they wander from home, and they can be set upon by bigger dogs, too; but they never die. -Phil" Indeed. Didn't someone ask a hundred years ago - if the universe is infinite and there are stars in every direction I may choose to look in the night sky, then why is the night sky dark and not light? Is the answer that photons come in discrete packages? You might have a small lightbulb making trillions upon billions of photons, but as they disperse do they end up as individual photons? But never less than individual photons? Quantum. And what, pray chance, should happen if they interfere with another photon along their travels? Do they entangle? Do they know they are going to entangle from the moment they set out, or even beforehand? I thought I understood the double slit experiment at school, but then I read about Bell's Inequalities and nothing makes sense. Bye bye local realism. Everything in the universe knows about everything else in the universe in all places and at all times in the past and future. There are some good explanations of this on the internet (not wikipedia though). I wish I understood it all. I wish I understood the practical applications too, like a colleague of my father's who is doing some fairly top secret work with quantum cryptography sending entangled photons real world distances. These are photons on which you cannot eavesdrop, because in doing so you alter the state of their entangled partner.
Right, back to reality. Tank circuit. 10mw power. CRO. Get something oscillating at 1.6Mhz via a propeller pin. Attach an antenna and see how far the data can go. I've got 3 metres without a prop - just a simple transistor oscillator.
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www.smarthome.viviti.com/propeller
Post Edited (Dr_Acula) : 3/19/2010 9:18:31 AM GMT