Thanks, that looks really useful.
I'll try my best to explain, though I have a habit of rambling so forgive me if I confuse you.
I have a model airplane with four servos for various controls. For this I'll just talk about one of them, the one that controls the ailerons (bits on the wings that wiggle to make it roll left and right).
This servo is connected to a radio control unit already which gives me my full manual control. Here's where I start to have my fun, I have an arduino with a bluetooth adaptor that speaks to an android phone that it placed inside the plane. The phone has all the sensors and internet access I need to develop some pretty cool stuff, eventually to the point that the plane will fly itself.
Right now the plane is set up so that when it tilts, the phone detects this and the arduino uses the servo library methods to compensate.
Now here's my problem, I can not in all good conscience allow Hera (the plane's name) to fly without having the fail safe of taking back manual control if the the phone dies.
What I can do is connect both circuits to the same servo with the ground to the radio control unit and the arduino being tied in together.
The arduino's signals from the servo library methods seem to be powerful enough to drown out all signals coming from the radio control unit. I'd thought that sending the:
command (from the servo library) would be enough to give me back control but apparently not.
The only method is to disconnect one of the wires that completes the circuit between the arduino and the servo, either the signal or the ground, this breaks the circuit with the arduino and gives back all control to the radio control unit.
Now I had thought of putting this electronic switch on the signal pin but I figured that considering I will eventually be having all four servos connected up, I may as well put it on the ground because after all, that would mean just one wire to be playing with, rather than four.
I hope I've made sense enough for you to picture what I'm doing, if you've better ideas for solving this, please tell, as I said, I'm no electronics expert