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Dec 05, 2007, 12:36 PM
Inciting Riots
village_idiot's Avatar
Hmmm.... I see what you are saying
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Dec 05, 2007, 08:17 PM
Registered User
Look around - I don't have the time at the moment but I think I remember someone took the time to look at the data and it wasn't encripted.
Dec 05, 2007, 08:35 PM
VE7FM
TheSteve's Avatar
Thread OP
I recall seeing that as well, at worst it seemed perhaps the bits were re-arranged.
Dec 05, 2007, 09:16 PM
Inciting Riots
village_idiot's Avatar
No AES? I thought that was built into the chips?
Dec 06, 2007, 12:40 AM
VE7FM
TheSteve's Avatar
Thread OP
The xbee modules can perform the encryption but are very slow at it. In the past JD suggested the PIC was handling it. If there is any encryption it only makes sense to have it in the PIC, otherwise monitoring the serial data going to/from the xbee would be trivial.
Dec 06, 2007, 09:33 AM
Initially, we used AES but it was too slow. So, I opted to do the encryption in the PIC itself.
Jan 12, 2008, 10:43 AM
I don't want to "Switch Now"
pmackenzie's Avatar
Steve,
I am about to start working on this for a JR transmitter, possibly with a PIC instead of an ATMEL, so i will need to work on the code.
One thing has me puzzled.
How does the module know where the frames start and/or stop
Usually with character based data you would use some special value as a synch or EOF, but since the way you outlined it the data is all just hex values.
What are they doing? Leaving a gap? Some other scheme?
I know there is a 0x00 as the first byte of each frame, but there would be lots of 0x00s buried in the channel position data.

Thanks,

Pat MacKenzie
Jan 12, 2008, 11:10 AM
Registered User
Quote:
Originally Posted by pmackenzie
How does the module know where the frames start and/or stop
The frames are sent every ~15-20ms, so I would most likely guess that the module syncs on the dead time between each frame. When I was hooking up my computer to the RF module, I found that I had to add a delay (at least 8ms) between each packet that I transmitted, otherwise the RX would not recognize them.
Jan 12, 2008, 11:29 AM
I don't want to "Switch Now"
pmackenzie's Avatar
Thanks.

Your Wii controlled heli is very cool

Pat MacKenzie
Jan 13, 2008, 04:17 AM
VE7FM
TheSteve's Avatar
Thread OP
I've never really thought about the starting/stopping. I assume it resets when it sees a new packet that begins with 00 00. I also never checked to see if it would actually transmit channels greater then 6 as I don't have a receiver that can do more channels.

The LP5DSM processor(Atmel Mega8) sends a packet the usual 60 times a second or so, after it sends the packet via serial data it generates the same as PPM for the trainer port.
With the code I am using a serial packet is sent as soon as we've received 6 PPM channels worth of data, we don't even wait for the end of the frame(to reduce latency) As I am decoding PPM from a standard radio I never really worried about the frame rate.
I've logged over 30 hours of flying time with my module, flawless operation with two different helicopters. It may all be coming to an end soon though as the x9303 I ordered back in October last year is finally supposed to be in stock on friday.
Jan 13, 2008, 01:21 PM
Inciting Riots
village_idiot's Avatar
I guess that means your 9C will be on the auction block soon.
Jan 13, 2008, 08:14 PM
VE7FM
TheSteve's Avatar
Thread OP
Possibly - its gonna be tough to part with. I figure I should sell it with the dsm2 module but its tough to let go of custom things you've built. Maybe I should keep it as a spare
Jan 13, 2008, 08:19 PM
Inciting Riots
village_idiot's Avatar
You could always look into a different radio like an EVO and convert it
Jan 13, 2008, 08:23 PM
I don't want to "Switch Now"
pmackenzie's Avatar
Quote:
Originally Posted by village_idiot
You could always look into a different radio like an EVO and convert it

He won't need another radio once he gets the 9303

Pat MacKenzie
Jan 13, 2008, 09:21 PM
VE7FM
TheSteve's Avatar
Thread OP
I hope its as nice as people say - I've never owned anything but Futaba. Gonna be tough to match the feeling of the 9C gimbals.


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