At power level 7, you'll see a stright DC level. When you set the power level to 6, you will see about 9 volts for 7 msec, and 0 volts for 1 msec. At power level 5, you get 9 volts for 6 msec, and 0 volts for 2 msec. The RCX output ports can deliver about 500 mA into a dead short and will enter a thermal shutdown mode before they wreck themselves. A typical servo takes about 200 to 300 ma when it is holding a load or moving to a target setting.
Micro servos take even less current.
Later on, I'll show how to expand your control options by removing components from this design. I buy these in service packs and just cut them in half to interface with custom sensors or output devices. The resistors and NPN transistor act as a simple inverter. This turns our 0 volt idle periods into the positive signal pulses we need to drive the servo signal input. The cap holds enough charge to power the servo and the inverter for the brief period of time that the RCX output is low.