I saw that article in EDN but I have a big problem with it. The transistor is a 2N3055 which is a power transistor. Notice the 33 ohm resistor to the base - there is no way that a normal printer port can supply that amount of current. Now if you want to drive only 100ma or 200ma then replace the 2N3055 with a small 2N2222 transistor and replace the resistor with 220,330, or 470 ohm resistor. But if you want to drive more current then you'll need a buffer between the printer port and the 2N3055.

Roger robot, over and out. roger@robotics.com