I just received a genuine 915 MHz air module and recommended FTDI cable from 3DR but it appears to be inoperative. I've tried it with two genuine 915 MHz air modules from 3DR and get no green LED from either. Both modules work when plugged into the APM 2.5.
The cable has a red wire in the 3rd pin from one end so I assume that corresponds to the air module pin that is marked "5V". Other than that, I see no way to determine which way the FTDI cable connects to the air module.
I've just found and attached the datasheet that I think applies to the 3.3V cable I bought from the 3DR website. Pages 11 & 12 have the pin-out. I will check ohm it out when I get home.
Meanwhile, are these cables known to be pinned correctly for the 915 MHz 3DR air modules?
Falcon
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I just got the time to check the 3DR FTDI cable. The ground ohmed out good but the Vcc didn't.
I plugged it in the computer and could not get any reading between the ground and Vcc.
I didn't think I had any but I found a TTL to RS232 converter in a drawer. I checked the pinout, plugged it in and it worked. I had a good 915 MHz connection between MP and the APM 2.5 with two air modules.
Time to arrange an RMA