Telemetry is a technology that allows data measurements to be made at a distance. The word is derived from Greek roots: tele = remote, and metron = measure. Systems that need external instructions and data to operate require the counterpart of telemetry, telecommand.

Although the term commonly refers to wireless data transfer mechanisms (e.g. using radio, hypersonic or infrared systems), it also encompasses data transferred over other media such as a telephone or computer network, optical link or other wired communications like phase line carriers.

I wish to have real time plane movement data on ground. There are two ways to have this data in Ground Station- OSD¹⁾ or telemetry. There are some OSD systems capable of transferring telemetry to GS- but the price is to high for me. And there is a problem with OSD as telemetry: to be able to review you need to record all flight video. I would like to have plain telemetry data in audio channel for later review/manipulation- witch can be written as simple text file to SD card.

As my DX6i is not intended to fly few kilometers, i dont need GPS data o screen. Just flight time and battery status. As for telemetry my idea is read GPS data with ATmega µC²⁾ and send via audio dowlink to ground station. If it goes well- add more sensors to it.

Greatest task was how to transfer data via audio channel. As i'm not very experienced in microcontrollers- i'm choosing Arduino. It's atmega based, highly popular. It should deal with this task. I have found one french guy did this, but all code is in C and comments in french. Blah, as i dont know C, even comments does not help. But suddenly I stept over SoftModem library for Arduino. It is capable to encode data as sound and decode sound to data. Highly configurable (hi tome, low tome, baud³⁾, and buffer size ). GOOOOOOD Later I can tune my tones for best performance in RT/TX audio channel.
Next step is to purchase Arduino and try to encode sample data into sound. And then decode data back from prerecorded audio. Arduino UNO should be fine for my researches. Later on I will get simple Atmega and create a live downlink to Arduino.