Electronic Boost Control

[avos at cochlear.com.au]

     Hi Everyone,
     
     I am a new comer to this mailing list, and I'm not 100% sure that the 
     information which I am after is applicable, but I'll tell you anyway.
     
     I own a 1992 Subaru Liberty (or Legacy) RS Turbo, for which I wish to 
     add an electronic boost controller. The advantage of such a system is 
     improved boost curve through the use of a PID control system instead 
     of the current proportinal pnuematic bleed control system so better 
     bottom end performance, and more accurate control of boost than the 
     current system which due to its dependance on the flow of gases, can 
     vary alot with temperature. Due to availability of development tools I 
     have chosen to use a 68HC705B16 as the microcontroller for this 
     system.
     
     My first query is to a power supply to produce a clean 5V from the 
     dirty 12V supply of a running engine. Does anyone have a schematic of 
     a typical power supply which may be used for such an application, be 
     it switch mode, linear, or whatever? I will need to drive a 12V pulse 
     solenoid valve, so will need sufficent curent to run driving circuitry 
     for this valve (I expect that this will be biggest current demand on 
     the system)
     
     My second query is in regards to the driving of the valve. It uses a 
     12V coil which requires around 800mA holding current. Does anyone have 
     any recommended methods to drive coils like this from a logic output?
     
     My final query is to modelling boost pressure in the manifold. In 
     order to test (and tweak to a certain extent) my controller code off 
     the car and avoid risk of over-boost, I would like to model manifold 
     pressure as a function of throttle and load for my car using no boost 
     control using C code. I have chosen to use a C compiler to develop my 
     microcontroller code, so I could therefore test my code using such a 
     model and allow many of the PID parameters for the controller to be 
     optimised intially so that only minor tweaking of these parameters is 
     required on the car. I have reasonable knowledge of how turbos work 
     and have written my own model, however it is not fantastic, and I have 
     no idea of the order of time constants for the turbo, and transfer 
     functions for calculating the volume of flow of the turbo for a given 
     exhaust flow etc. If anyone can point in the direction of anyone who 
     might be able to help in such matters it would be greatly appreciated?
     
     The issues I have raised are not purely efi, but I hope that they may 
     be relevant to this group. Also does anyone know of any information 
     sources for DIY electronic boost control.
     
     Cheers,
     
     Adrian