Hi, just got this idea, and thought perhaps it would interest one of the clever guys out there. Hope is that a vendor will take this up, after a couple of clever LMRians have talked more about the details that I am too stupid to get into :)
It is a boardthatalwaysshowsyou "north" - a fixed point anyhow. Purpose is to navigate, for example in a football match.
Turn on board, and it has a radio, like a human-music-radio-thingey. Only it does not play music, it has the ability to tune in to a radio station, but only listens for the carrier wave.
It simply has a pointing areal, is "a crap radio that needs to be alligned to the sending mast", and an 0-5V signal is the output, more or less, after how strong the recieved signal is.
On the board we place 3 such tuners. (I am sure they can be bought/made for nothing, no?)
The antennas on them points to each direction, sort of like a Mercedes logo.
The board has a small processing / logic part that compares all 3.
It finds the 2 strongest recievers, and according to their individual levels, the point between them is where "north" is.
Output is a direction (0-360 degrees), always fixed towards the radio mast.
There are more complex ones in the sales, where you have to place "the sending masts" yourself. but how cool is that, when you can just tune in to a radio station?
I think such a module could be build cheap, compared, and I think most roboteers would really like a sense of direction, cheap and easy!
You could mount a small pocket radio on a servo. The radio could be modified with a directional antenna (see here, how to do).
I guess not every radio station is based in the North, so you would need to pre-selected one certain radio station. I would not use 3 radios as they would interfere with each other.
I am … well, try and read the above again I am not talking about a slow spinning of the antenna.
And we do not need to know where we are and all that, from a radio direction finder.
3 analouge signals, 2 of them are stronger than the third. The relationship between these 2 is our output.
I am talking about a simple little board that can be tuned to find any radio station, like you auto tune a radio. Then it constantly monitors the 3 radios, and tells you from 0-360 which direction the signal appears to be strongest.
You get a constant feed from it; Transmitter is now at 275, 277, 271, 265, 264…
As mentioned, the 3 radios will interfere with each other. I guess, it will also be not possible to get a 1° resolution with 3 fixed antennas. If you ever tried radio tracking you know what I mean Instead of the 3 radios I would use at least one, and switch/change the antennas in fast order
that’s weird its working normally over here and its not a compass module , its somehow a tutorial on how to make a compass using hall effect sensors , pretty interesting , i wanted to make it , but the parts needed are unavailable over here . if you want i can try and upload it somewhere ?
Ok, You do not have to use 3 radios, if they interfere, though I must admid that surprises me, that you cannot have 3 radios next to each other?
But then the one radio will switch between 3 antennas. Oh, you write that as well, yes Well, we could have a complete circle of antennas, and switch between them, if this is easy to make, and give a better result.
I am sure I could not get a 1° resolution, but this is not the point!
The point here is to have 3 fixed antennas, and to compare the signal recieved on one carrier wave from a normal music-radio. And from that give a value, continuesly.
Why? Because this would be a fun, new and cheap way of getting a fixed direction for small homemade robots. It would definatly be a bonus if it had an output to actually listen to the music
Play with two radios next to each other, you will see how they interfere Most receivers are in the same time (weak) transmitter. To get an usable signal, the antennas would need to be arranged in a bigger distance, not only a few centimeters from each other.
AM radios are easier to build than FM. There is a IC called “Radio in a chip”, looks like a 3-leaded transistor, type is ZN 414. I am not sure if this chip is already out of stock, instead you could use ZN 415 E (6 pin DIL version). You have mentioned last time a very nice circuit page “200 Transistor Circuits”. There you find following application for the ZN414 (Search at index for “IC Radio”):
I have built some radios with the ZN 414 E chip before (one powered by fuel cell/photovoltaric array and one powered by a stepper motor which I misused as a generator :)) Here is a PDF version of my stepper motor radio (sorry, only in German available). But I do not know if still AM radio stations are available in Denmark.
Very interesting, thanks. And In fact I have some of them radios on a chip laying around - never knew what to use them for
However, how would one get signal strength from this? It would not be very nice if it was according to volume of the speaker connection in the circuit.
I am looking for the carrier signal, how strong that is. Do you see how that could be obtained?
Thanks a bunch, I am starting to like you even more!
That’s the hard part:) But you could start with the volume. Keep it simple and stupid principle. I would start to experiment with a pocket radio. Replace the loudness potentiometer by a resistor, pre-select the strongest broadcasting station on your frequency band (for instance 101 MHz, this is your carrier frequency), connect the output of the radio with your PICAXE ADC and see what happens if you move the radio around. The problem with the volume is the kind of stuff they send (music, speech, break, advertisement). Many years ago there was a kind of endless repeating beep tune on one end of the AM or FM band. I do not know if this kind of beeb tune still exists there. I have a pocket radio (Pocket radio with LED tuning indicator) with a small red LED. If the signal is good, the LED begin to light continuously. If I move the radio then around in a circle and the signal gets weaker, the LED begin to flicker and finaly goes out. Would be easy to hack this kind of radio and connect it to an ADC input of a MCU instead to the LED.
Remember now I also did some experiments with a satellite signal strange analyzer, delivered with a TV satellite dish to find the strongest signal to align the dish. Maybe could be used too for your attempt.
Well, simple for the stupid it is going to be. Because I know this can be done that way.
However, I am not sure the simple way is by hacking excisting equipment. And I think the approach of using the “sound” instead of the carrier wave is totally wrong.
Also all the audio amplifying is IMHO making it all more complex.
There must be a simple way to just tune in to a carrier wave, and see how strong that signal is. A few components. I know that OddBot can do this, but he is so busy
Just tuning in to the carrier wave, and compare to other tunings how strong this is. If onnly I know how to do that tuning, I could do the rest myself. Hmm…
I am researching small uni-directional antenna. The problem with our size requirements is evident: we want our antennas to be so darn small! The laws of physics are not very accommodating.
For instance, a typical AM signal @ 800 kHz has a wavelength (lambda) of 375 m. A standard whip antenna has 1/4 wavelength ~ 94 m. Any shorter antenna would be less effective.
The higher we get in the RF spectrum, the shorter the waves get and also the antennas. Typical FM signal @ 100 MHz -> lambda ~ 3 m. Typical Wifi router @ 2.4 GHz -> lambda ~ 12 cm.
So here’s the big question: would a Wifi router (or a cell phone mast) also work for our application?
Sure, WiFi routers and Cell Phone masts would be cool and the gang!
Since we do NOT want a perfect signal (because then there was nothing to measure in difference), would it not be cool with a crappy antenna? 1/8 of the wavelength or something like that?
On another node, to quote OddBot from a private mail: “3 simple crystal sets and a low power transmitter should work” - what ever he means by that (?)
A crystal set is a type of receiver that can receive AM radio. It uses no battery or other internal power source. The radio waves are picked up by an antenna, resonates on a coil/capacitor circuit and rectified through a diode. This signal can be strong enough to drive a crystal earphone (which has a very high impedance or internal resistance to audio signals). The receiver also needs a good “ground”.
Oddbot is probably thinking that a Picaxe ADC also has high impedance and can replace the earphone. For our purposes, the antenna/ground combo would need to be highly "directional". And mobile. And small. I doubt if a smallish antenna would be able to provide a detectable signal. Please let someone prove me wrong!
This is not done with a few simple components, Fritsl. You can tune a radio in different ways - change the value of the inductor, change the value of the capacitor or use avario cap
To design a according receiver with vario cap frequency tuning is not so easy, requires a lot of knowledge and (in part) complex calculations of RLC circuits.
PS: A crystal set you tune by changing the inductor (inductor tapping) or capacitor (variable capacitor). The antenna must be long (5 to 10 m) to get a usable signal. The circuit also must be grounded, but this is out of question for a mobile robot.
I am not talking about a slow spinning of the antenna.