I have used a LM317 as a constant current source, see the schematic.
The only problem is the resitor, if the current should be limited to 350 mA, the resistor should be 3,6 ohm.
The transistor is a BC547
A better way to use the LM317, see reply #7 in this thread:
http://arduino.cc/forum/index.php/topic,102101.0.html
