I am just getting started on this project and I’m hoping someone, that has accomplished this or has the experience to point me in the best direction, to do so. I just want one radio to transmit data from the adruino (altimeter readings) to the other attached to my laptop. I found this one reply to antoher topic from the
skimask -
"I hacked a pair of those cheap FRS radios to send what amounts to DTMF tones over the air. Worked like a champ.
$20 for the radios at Walmart or wherever you find them on sale, a bit of cutting, some soldering, some FFT code on a PIC on the receiving end, another PIC and some DTMF code on the TX end.
Done and done."
This is what I hope to accomplish, I would like to know more specifics (if possible). Any help will be much apprecieated.
Shawn
No specifics I can give you because you don’t have any specifics to give us.
http://www.catb.org/~esr/faqs/smart-questions.html
TX
PIC with a relay running the P-T-T button
PIC driving a speaker positioned right in front of the microphone spitting out DTMF tones
RX
Microphone sitting right in front of the speaker
Microphone connected to an op-amp putting out ~5v pk-pk for the A/D input to the PIC
PIC running some FFT code to figure out which tones were sent
Profit
The only thing that’s not straight forward is the FFT code, and it’s not that it’s proprietary code or anything. I don’t fully understand the math behind it. I made it work for me in my particular situations and unless you’re sitting right here next to me with your hardware, your firmware, your SPECIFIC set of circumstances, I see exactly a zero percent chance of me helping you get your project up and running…especially when PIC’s and Arduino’s are inherently incompatible at the assembly level.
skimask,
Thank you for your reply. Sorry for being vague, I am just starting this project and needed to know where to make RX/TX connections on the radios to get some kind of
signal; this you have provided!
To start, I will try to connect an arduino and a cobra micro talk 2way radio for transmitting a signal to the other radio only (probably not hard for you experienced,
however I’m not).
Once this is complete, I will then try to receive this data into my laptop and eventually decode.
Anyway, I am currently looking into communications on CMOS levels. I will have more precise questions as I (hopefully) progress. In the end, I hope to make a rudimentary
telemetry system that sends altitude from a model rocket to my laptop in real time. To clarify, I just want to make a RX/TX connection (for now) then build off this.
Any suggestions are more than welcome.
Thanks for your time.
Shawn
On the receive side, you could use a DTMF decoder chip rather than the FFT math. Adds a chip, but removes the math complexity.
Breadboard arduino (or stand alone) + [this is the cheapest way I’ve found for RF serial communication. Should get any distance you want if you’re going vertical (always line of sight) with a homemade directional antenna. Jeelabs has a good library that can get you working between the arduino and the RF module with very little tweaking. This route will require you to build your own breakout board for the RF module. But, that’s just more free education 
It can also be done with [this which a similar RF module already mounted on a BOB.
But, for that price, just buy a jeenode from modern device and have the RFmodule and an “arduino” in one. The “arduino” is not 100% compatible since it runs 3.3V at 16Hz which is out of spec for Arduino. They are available premade or assembly required. They also have a 915MHz frequency option unlike the above modules which are only available with 433MHz transmitters.](SparkFun RF Transceiver Breakout - RFM22B-S2 (434 MHz) - WRL-10154 - SparkFun Electronics)](http://www.sparkfun.com/products/9582)