(NOTE - Nov, 2012 - the original grill block described in the first part of this thread didn't work well. Jump to post #94 to see the redesigned version.)
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I've been poking around with the Arduino for a little while trying to figure out how to get this project to work. I've compiled a bit of info on it, but Darin finally bugged me enough to get me to post the info as some help definitely wouldn't hurt. Also,
this is by far not an area of expertise (electronics) for me. I know just enough to start getting me into trouble. I've only gotten this far through a lot of web surfing and reading up on things and some help from dcb (thanks again). So, I'm throwing out my initial designs for you to all look at, tear apart, and come up with something good we can all use.
Anyway, this is the general idea. Use the arduino to monitor a temperature sensor. This is an additional sensor (no splicing into existing car wiring) will be monitoring coolant temperature. It will be mounted in a radiator hose coupling that will need to be spliced in after the thermostat. Monitoring the temperature from this sensor, the arduino will output commands to a h-bridge which will control a simple two wire electric door lock actuator. This actuator will close and open the grill block door. Sounds pretty simple eh? Well, its not, at least not for me.
The current problem I'm having is finding an acceptable h-bridge. Almost everything I seem to find is surface mount, and I'm not even exactly sure what specs to look for in this thing. I think I found an acceptable one. Its the
TLE 5205-2. Its in a P0-220-7 case so it can actually be worked with. The down side is its (I'm guessing) overkill as it can handle 5A continuous, and its also a bit pricy at $7.50. As I was browsing mouser and digikey there were a lot of cheaper chips, but as I said, mostly surface mount. I'd obviously like to keep the price down where ever possible.
Here is the list of necessary items:
Arduino of your choosing
LM61 temperature sensor in a TO-92 case
Electric door lock actuator
h-bridge
radiator hose coupling (local automotive store, mcmaster)
wire
grill block of your design
I have most of the arduino coding done, but I'm not going to bother posting it as it may change depending on the h-bridge.
All in all, I think this can be put together fairly cheap. I've looked into other ways of doing this and this is easiest, most customizable and cheapest way I've found.