I need to isolate a Resistor Capacitor circuit from an input. The goal is to provide power for a short period of time to an input and LED but, I don't want the resistance of the input to effect the discharge time, since this resistance may be unknown. Also the RC charge time has to be very short on the order of uS but the discharge time needs to be on the order of Seconds. Can this be achieved with an optoisolator?