That was luck! I used the stepper shield and an Arduino to drive the motor (stepper), simulating the movement across the arm in search for the vein. Everything worked fine and I just used a 12V power supply for the (yeah, too little) motor. After a minute I reallised something smells funny - the second motor was overheating. Must try with less voltage next time :-)

Today the video of the first build attempts is ready. I will show tomorrow how veins look in infrared light...