by Eric Brouwer » Wed Aug 17, 2005 1:16 pm
For the more technical readers, I have tested two Dragonfly radios, and think I know why some radios work with PPJoy, and others not. The output signal on the S-Video plug for tx 1 is only 2.5V, and for tx 2, 3.5V. Tx 1 fails on PPJoy, but Tx 2 works fine.
Furthermore, the signal with the supplied cable is the wrong polarity, and the ground of the radio must be connected to pin 2 (Receive), and the signal to pin 5 (Ground) on the DB9 plug. However, tx 1 still failed to respond on my PC. Failing to get the polarities correct, resulted in the "invalid synch bit".
The IEEE spec for RS232 ports state the following:
Receive threshold: +/- 3V. As the output of tx 1 changes only between 0V and -2.5 V, it is below this threshold, and not detected on the com port.
This can be the reason that some of the radios does not work, as the level is too low for some of the com ports to recognise the mark/space transition.