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Author Topic: 2 way radios as transmitter and receiver  (Read 3224 times)
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I have been looking at long range radio transmitters and receivers to wirelessly control my tracked robot, but all of the ones I have seen are either too expensive or lacking the range I am looking for. I have seen projects where people have used 2 way radios for wireless communication between arduinos, but none of them have explained how they went about doing it.
Does anyone know how to wire one up to the arduino, or if it is even worth taking one apart?
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You could send equivalent of morse code messages from radio to radio, interpret the dots-dashes on the receive end and act accordingly.
Output audio on one end,  decode the dots dashes on the receive end.
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Using the morse code idea, I may be able to take out the audio completely by cutting out the microphone on the transmitter end and speaker on the receiving end. Then I could just pulse the code through where the microphone was.
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The 2way radios are usually narrow band FM with 5-15kHz bandwidth. So you can transmit data via the mic (or better directly into the modulator), and receive data from the demodulator output (so before audio amplifier, as the audio amp may limit the bandwidth). It will work at least 2k4 baud or more. The amateur radio people use it with packet radio (up to 9k6). You may try the virtualwire interface, or Manchester coding, etc. Google "packet radio modem", "arduino TNC". You can build the modem (for tx/rx) with arduino for sure.

http://en.wikipedia.org/wiki/Packet_radio

PS: using 2way radios for data transmission might be a subject to your local telecom regulation.
« Last Edit: June 19, 2013, 02:28:47 pm by pito » Logged

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PS: using 2way radios for data transmission might be a subject to your local telecom regulation.

I was about to post something different, then I saw your last line. This needs to be stressed; depending on what you plan to use as a 2-way transceiver system, you will need and want to find out whether you can even transmit data over it in the first place (with or without a license).

For instance, here in the United States, while you don't need a license to use a "family radio" or to use a CB (citizens-band) radio, technically, you aren't allowed to transmit data over either. I'm pretty sure that even if you have a ham license, you can't do it - at least on those bands.

Now - you could probably get away with it, at least in the short term. Maybe if you channel hopped as well, you could get away with it longer. But sooner or later, you might have the FCC knocking at your door (again, here in the US). Actually, I'm not even sure that would be the case, even in the case of CB radio (which seems to be mostly "dead" as far as usage in some areas).

I'm not sure whether the same would apply to cheap FM toy walkie-talkie systems; likely for these nobody would give a damn except for any other kids in the area (though again, their interference is -your- interference as well - so take that into account).

Now, if you have a ham license - the possibilities will open up quite a bit (though the amount of money needed to implement the systems may also increase); personally, I would just stick with whatever I could get off the shelf, and try to keep things within legal power limits, to limit my exposure to all sorts of fun limiting authorities.

There's plenty you could do with everything from xbee, 802.11x network stuff (technically xbee falls in this realm), 2.4 GHz R/C systems, and those other small transceivers that operate in the 900 MHz and other bands (not to mention some of the bluetooth stuff). These, coupled with appropriate antennas, can easily cover a quite large area for control, telemetry and other operations, and won't get you in trouble with the law - if that is a concern in your locale.

If you need longer distances, there's always cellular-based data systems, and if you need really long distances that can't be spanned by the cell phone network (ie - things out in the hinterlands) - satellite data is also possible (though not cheap).
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The major issue you need to address is what data rate do you need to control the robot.
2 way radios are very slow in sending data because they are 1/2 duplex, ie you can send or receive
but not both at the same time.
Ensuring that what you send actually gets to the other end is a complex process involving sending then receiving
then sending again.
The actual data thruput can be as low as 100 bps , even if the radios can go faster.
With unmodified radios you are limited to around 1200 bps .
Going faster needs modifications to the radios which normally you cant do unless you have the circuits of the radios.
Id be looking at using broadband wireless using the cellular radio system to get more speed and reliability.
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