Hello all! I'm new here, and like many arduino enthusiasts I would imagine are, electronics is not my first subject, been having good progress with the UNO and are about to upgrade to the mega, for more sensors, but I've come to a bit of a snag as im unsure what to do for this current system.
I'm building an autopilot system and are trying to make it possible to entirely isolate the processor for manual control, incase of a complete failure of the arduino board or its code. (The code is entirely custom, its my university project)
What I want to be able to do is have a unit that will allow switching between the servo signals the processor is putting out, and the servo signals the radio is putting out. I've got two ideas on how to do this -
opto couplers - simply provide power to the anode of one set of couplers to allow them to send a signal forward, and on the other set do not provide power, allowing only one group of signals forward to the servos
Considered couplers - http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=7085402
darlington drivers - provide power to the common to allow the drivers to function as above but what concerns me is looking at the circuit diagrams, i cant see what would stop the drivers sourcing power from the output pins of the other darlington driver and try and let signals through anyway. The way I see it I would need diodes on all output lines to stop that?
Considered darlington array - http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5401076
I'll probably use something like a PICAXE08 to drive the isolator, as its quick to program cheap and small. Not powerful, but doesn't need to be since I only want to decode one servo line off the receiver with it to send out an "on" or "off" pulse.
Any advice? I won't get a processor to divide the signals, if the processor on the isolator fails, I want it to default to manual.
EDIT : ah, heres an interesting thought i didnt think of.
if I wired the Ground of a darlington array to a pin on a controller, and set it to HIGH, with the same VCC, that should essentially shut down the driver, right? (then again, thats kinda doing the same as not adding a common, isnt it?)