View Single Post
Old Jan 13, 2010, 03:55 PM
bluesky123 is offline
Find More Posts by bluesky123
Crash=change of flying medium
bluesky123's Avatar
Boulder, CO
Joined May 2002
1,375 Posts
Quote:
Apparently it is still available in two types, with the less expensive version able to handle 4 channels and the other at $40 having 7 proportional channels plus 4 buttons ...
The main difference between cheap and good interfaces is not the number of channels (it costs nothing to support up to 8 channels!), but the signal resolution, channel mapping, internal calibration, and extra features.

Take a close look at any Chinese interface, like most of the vendors are selling, and notice its resolution in Windows control panel/Game controllers/Calibration while 'show raw date' checkbox is checked--you'll see that the signal level changes at most within 0...255 range (8-bit resolution). Most likely the range will be less, something like 60...180 (about 7-bit resolution), since the PPM pulse duration is usually hard coded for maximum channel travel, +-140%, while your transmitter is set to normal travel volume. Most modern transmitters have 10-bit resolution, so, using them with one of these cheap interfaces means that the joystick moves with considerably, 5...8 times, lower precision than you are moving your TX sticks! One can argue that 7-bit resolution is ok for flying a trainer plane in a sim, but as soon as you switch to a 3D plane or heli, this will become a problem.

There's only one interface sold today (a shameless plug...), which digitizes PPM signal at 16-bit resolution, then does digital signal filtration, and sends 10-bit signal to the computer:
http://milehighwings.com/index.php?cPath=35
In addition to the higher resolution, this interface offers internal calibration, which ensures that each channel, no matter what channel travel is programmed in the TX, spans the whole 0...1023 range. It also offers arbitrary channel mapping, flexible button assignment, PPM output mode, and ESC programming feature (with an extra cable):
http://milehighwings.com/manual_usb_v4.htm

Boris
MHW R&D
bluesky123 is offline Find More Posts by bluesky123
Reply With Quote