Posted by Greg Fletcher on November 7, 2009 at 9:52am
I have just perfected (finally got to work) a method for sending data up to the plane while in auto and without missing a GPS frame. I've been using all my spare time for a week to get it.It works by sharing the uart time wise. The U-blox sends data for ~28ms 4X /s. That leaves a lot of time to receive from the X-bee. The X-bee has a 256 byte buffer the will hold data until the ardu asks for it.If the RTS(request to send) is not connected the data goes right through. If the RTS is held HIGH. the X-bee will hold the data packet until RTS goes LOW. Packets must be less than 256 bytes. No problem!I connected the RTS to D7 on the ardu and the Tx from the X-bee goes to a diode to the ardu. Basiclly two diodes pointing away from each other and a 10 K pull up resistor. The cathode of the other diode goes to the GPS Tx. The middle goes to the ardu Rx. After the data is read from the GPS and the extra bytes in the 368 uart buffer are cleared (read and dumped), D7 is set low and the X-bee sends received data to the ardu, when that's done D7 goes HIGH again. I used Jordi's "decode" from the GSin the ardu to read and process the received data. BTW I have a pretty good dual trace scope that I used to see what was going on. Impossible to debug without one. Will post more details and code later.I just now got it to work and have something I got to do right now. And I'am not using the shield, but it should work with one.
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