I want to design a diffuser that can change as the speed does, as in open and close. I assume I will need to add some sort of small motors that will move the components to the required position as the speed changes? Also, how will I connect it to the speedometer? Correct me if I'm wrong but I will need to have some component (like a CPU/control unit) that would be connected to both the speedometer and the diffuser that will control the function? My uncle did something like this 30 years go but sadly he has passed away do I can't ask him.
OK, starting with 3 caveats: 1) I am guessing you are talking about a relatively modern mass produced car, if not then the way of getting a reading from the speedo will be different. 2) This is not something I have ever done myself. 3) I make no claims for the speed of response or stability of the resulting system. One way I think you could do it, is to read the OBD (you can but kits), then use a PIC micro-controller or similar to control a motor driver, to drive the motor, to move the moveable surface(s).
Thank you for your reply. They are all modern cars. Where could I buy a OBD kit from? also, where would you recommend buying the motor driver, would you know what would be the best quality?
After googling: http://www.nerdkits.com/videos/obdii/ https://www.sparkfun.com/products/9555 http://www.raspberrypi.org/forum/viewtopic.php?f=41&t=8854 http://www.obddiag.net/obdcan.html Not all for PICs, depends on what you are comfortable programming. You have to get a motor driver to suit your motor, so you would have to spec the motor first. In the past I have used and was happy with lin engineering for motors and drivers: http://www.linengineering.com/ But there are many alternatives, MDF will have threads on this. http://arduinodev.com/connect-arduino-to-a-car-through-obd-ii-port/ http://arduinodev.com/hardware/obd-kit/ See above for a couple of reference pages on connecting Arduino to OBD.
A quick google search turns up. http://www.nerdkits.com/videos/obdii/ which seems a decent explanation of what you are trying to accomplish. They read it out and the response seems pretty good.
As the US government started to increase emission standards on cars the designers of carburetors with an adjustable orifice using the suction pressure within the carburetor and linkage. Please consider finding some of these designs which appeared in magazine like Popular Science or Mechanics.
