[aprssig] Soundcard Decoding in a new light

[Mark Fellhauer]

An odd thing, but I recently bought a small RC helicopter called a Blade 
CX2, it comes with a 2.4 GHz DSM RC transmitter.   On the back of many RC 
transmitters is a trainer port, that allows a novice flyer to "buddy-up" 
with an experienced pilot with a similar RC transmitter so that if the 
novice gets in trouble, the trainer can take over.  Kind of like the 
student driver car...

Another use of this trainer port is to hook up your RC Tx unit and use it's 
joysticks with an RC flight simulator on a computer.  This way you can get 
in some stick time without risking an expensive model in the real world.

Most of these trainer ports I've seen are some sort of DIN connector - some 
even looking like an S-VHS (S-video) connector.  But on my new 2.4 GHz TX 
box, it appears to be a standard 1/8" audio jack.

Doing some research I found a freeware RC Flight Sim Program called 
FMS.  Wanting to use my RC Tx for training I did some more research and 
found a program called SmartPropoPlus.  This program takes your soundcard 
and converts the signals from the RC transmitter's joysticks into something 
flight simulator software can understand.   I plugged an 1/8" stereo audio 
cable in the back of the Tx box and the other end into my soundcard's 
line-in jack.  I immediately heard a rumble/buzz that sounded somewhat 
familiar...  Moving the joysticks caused the rumble to change pitch.

Sound familiar?  Sweet!

http://www.mh.ttu.ee/risto/rc/electronics/radio/signal.htm

http://www.aerodesign.de/peter/2000/PCM/PCM_PPM_eng.html

Mark
KC7BXS