I recently bought a Garrett GT2256V electronically actuated variable-vane turbocharger. Using some hints from the guys a the superturbodiesel.com forums [link], I wrote an Arduino sketch to control the Hella actuator on this turbo.
here's a video of the actuator in action! http://www.youtube.com/watch?v=ENSbcuCAXt0
here's the source: http://jason.pepas.com/code/hellasweep/HellaSweep.pde
parts of the program were inspired by Ken Shirriff's excellent article on arduino PWM stuff: http://arcfn.com/2009/07/secrets-of-arduino-pwm.html
here's the hex (compiled for atmega168): http://jason.pepas.com/code/hellasweep/HellaSweep.cpp.hex
Hella PWM interface
the guys at superturbodiesel.com figured out the pinout [link]:
pin 1: 12v pin 2: GND pin 4: control (PWM)
The Hella actuator acts much like a servo, interpreting a PWM input signal as a position command. However, the Hella actuator responds only to a narrow frequency band. I used the above code to experimentally determine the limits of this frequency range. The frequency range which worked for me 135 to 146 Hz.
Additionally, the guys at superturbodiesel.com discovered that it also only responds to a certain range of duty cycle. My findings pretty much corroborate their's. The actuator doesn't seem to move any lower than a duty cycle of 15%, and above 98% it appears to assume the input has been shorted to 12v.