We wanted to build a model police car with working lights and sirens. Then we decided to add a motor and instead of using a switch to turn everything and off we used a photodiode. For our car the photodiode signal is a simple on off switch. If you want a more complicated device that will respond differently to different signals (only do lights, or do lights and drive but no sirens) then you will need a significantly more complicated setup and code. 

Step 1: Gathering the Necessities

Materials, (suggested sources):
-Plastic Model Car, preferably snap together. We used a 1:25 scale and that seemed to be a little on the small side (http://www.amazon.com/gp/product/B000JSNYU6/ref=oh_o00_s00_i00_details)
-3 Superbright red LEDs (http://www.sparkfun.com/products/528)
-3 Superbright blue LEDs (http://www.sparkfun.com/products/529)
-A small buzzer or speaker (http://www.sparkfun.com/products/7950 or http://www.sparkfun.com/products/9151)
-A small motor (http://www.sparkfun.com/products/10171)
-A Darlington transistor (http://www.sparkfun.com/products/312)
-A photodiode (http://uk.rs-online.com/web/p/photodiode/6655331/)
-A flashlight, preferably quite bright. Or possibly a laser pointer, experiment!
-2 9V Batteries
-1/4 Watt Resistors: 6 330 ohm resistors for the LEDs, a 100 ohm resistor for the buzzer, a 10,000 ohm resistor for the photo diode.
-Perforated PVC sheet or printed circuit board: You can design and print your own circuit boards if you have the resources. It will make for a tidier interior of the car and an easier soldering process. You can also wire and solder to a perforated sheet of PVC.
-Solder and Soldering Iron
-Breadboard for testing setups
-An Arduino Uno
-The Arduino program
-Gears for your motor and axle?
-Multimeter for testing
-Paint and decorations for your car

If you can get a good gear ratio for your motor the the car will actually be able to drive. We found that the car was too heavy to drive at our current gear ratio, but ran out of time to change it. You may also need to consider getting your car lifted after all the circuitry is inside it. You could also use a larger model and a more powerful motor. Or really just a more powerful motor. 
maybe you could paint the windows/wires black so the wires don't show
but it is also nice without
I love it. The Camaro Police car idea reminds me of Saints Row 3
Turns out it drives by itself on a slight incline! CHeck it out at: http://www.youtube.com/watch?v=Kx1m3e634-0&feature=youtu.be
Love doing stuff like this. Your model looks really cool. I'd like to do something like this with the kids over the weekend.
Thanks! I'd recommend using a scale larger than 1:25 and a lego gear/axle/motor setup if you can.

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