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Originally Posted by Mike Betts
Dr. J.,
I would disagree. The TTL port is meant to be used by a device which derives it's power from the RC (such as a SMiRF or CMU2cam).
I am unsure if the RC has an optocoupler on this port. I rather doubt it. and you don't want the power supplies of the RC's fighting each other...
Unless IFI says different, I would wirewrap a small optical interface board where the RX side of each channel was powered by the receiving RC's +5V and GND. There are many optoisolators which can be used. As an example, I would recommend the HCPL2300 IC chip with a 3.3K series input resistor and a output inverter/buffer for this task.
If IFI says it is OK, you could connect only TX RX and GND and not connect the +5 power between RC controllers.
Bottom line, I would not direct connect without talking to IFI first.
Mike
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Yes, optoisolators would be nice to have, and I certainly understand your worry about frying electronics if the ground potentials were different, but I can't see anything bad happining if everything is battery powered (and referenced to the battery's ground terminal). Bad things will likely happen if the two devices are powered by separate AC/DC converters, where the grounds can have very different relative potentials (I know you know this Mike, but I suspect a few people reading this don't).
-Kevin