13BRV3
Posts: 235
Joined: 10/14/2006
From: Navarre,
FL, USA
Status: offline
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Greetings,
I've been following Mike's brushless conversion thread pretty closely, and that prompted me to do a little snooping with a scope. When Futaba came out with their 6 channel 2.4 GHz system, I bought two, and a few extra receivers, then promptly sold all my 72 MHz gear on Ebay. The only thing that remained on 72 MHz was the DF, and it really bugs me, though I realize this is largely a personal problem 
A few days ago, I asked Mike Dammer if there were any plans to come out with a 2.4 GHz DF, and he said no, because it would interfere with the cameras. He's right about this, and I've had to get cameras on 900 MHz, and 1.2 GHz to avoid it with the fixed wing planes. Since I really want to use 2.4 GHz for the DF, I decided to see if I could make it work.
There are two main versions of DF boards, most have the built-in receiver, and the latest have a Berg receiver attached to the vertical board. I only have the old style to play with, but I have to believe the Berg style may be even easier to convert. On the old style, they receive the signal, but don't separate it out into individual channels like a normal R/C receiver does. Instead, they send the combined signal from the vertical board to the controller on the horz board, then let the controller do the separation in software.
I've never had a Berg board to play with, but they must either pick off the combined signal inside the receiver, or they have some hardware to recombine the channels so the controller will get what it's used to seeing. They might even reprogram the controller for the Berg. If they actually take the normal outputs, and recombine them in hardware, then it would seem like you could use any receiver in place of the Berg, as long as you get the signals in the right place.
Since I have the old board, I figured I either had to find the combined signal inside my Futaba receiver, or come up with hardware to recombine the outputs into a signal that would make the DF happy. I think the latter would be a better solution, since you could use any receiver without modification, but I'm pretty far out of the loop on current hardware design. I'm planning to try to figure out how to do this, but that solution will have to wait a while (hoping someone else will design the hardware).
I took my (employer's) trusty scope, and poked around until I found the combined signal in the Futaba receiver. It really wasn't that hard to do, since it's fairly obvious which chip does the decoding. The REALLY hard part is trying to solder a wire to that microscopic contact. The other problem is that the pulsed waveform is inverted from what the DF normally sees, but this is fairly easy to fix in hardware. Actually, it would be easier if Radio Shack still carried logic chips, but I guess they don't anymore. Did I mention I was pretty far out of the loop on hardware I needed an inverter, and don't have one, but fortunately I had a nand gate chip which will do in a pinch.
After inverting the signal from the bowels of the Futaba, I noticed that there were still some differences in the waveform, but it all seems to be in the 6th channel. For some reason, Futaba seems to have an extra delay before outputting the 6th channels, and the DF receiver doesn't. My hope was that the DF would handle the first 5 channels fine, and I wouldn't care if the 6th came through or not. Amazingly, and much to my surprise, that's exactly how it seems to work, though I'm suspicious that the 6th pulse is going to rear it's ugly head somewhere it's not supposed to be. Too soon to tell.
Well this is getting way too long now, so here's a link to my bench test video from this afternoon. It's about 35 MB, in windows media format, and no, I don't recall why I was so fascinated by the 5th channel switch
http://www.radrotary.com/2dot4GHzDFtest.wmv
This is very much a works in progress, so don't get too excited yet.
Cheers,
Rusty
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It's alive... on 2.4 GHz - 
RE: It's alive... on 2.4 GHz - 