I have an RC vehicle project with an onboard PIC that needs to read several
servo signals that come from a Futaba receiver.  With my old (~1984)
receiver, the signal wire was able to drive a NEC optocoupler, with a 220
ohm resistor in series.  This allowed me to interface the radio to the
computer without having any direct electrical connections.

But the new Futaba radio that I bought this year has a "weak" signal wire.
If connected directly to a PIC input pin, I can read it with no problem, but
it is incapable of driviing an optocoupler under any circumstances.  It
behaves as though there was a 1M resister wired in series inside the
receiver.

My question is: what is the best way to interface the radio to the PIC?  The
only two choices I have come up with so far are:
1) use the radio's power to amplify the receiver signal, and then feed that
into the optocoupler, or
2) directly connect the receiver signal to the PIC and assume that the
prospects for interference between the systems is minimal.  I have never
observed any interference in bench testing, so I'm not certain its a big
concern.  I just notice that people like Vantec always advertise that their
systems are opto-isolated.

thanks for any suggestions

Nicholas