My name is Marc DuBois, and I'm one of your ASE certified master automotive technicians at Advanced Auto Pro's. I have an intense interest in electronics, and I spend most of my time away from work studying this subject. I am currently working with a robot, manufactured by Parallax inc., called a Boe-Bot. This robot contains an embedded computer system. An embedded system is a computer system designed to perform a single, or relatively few, functions. Your vehicle contains an embedded system, which consists of a central processing unit, software, input sensors and output devices. One of many possible sensor configurations that can be used on the Boe-Bot is photodiodes. These are essentially light sensors. The CPU constantly watches the input of light sensors to determine where the most amount of light is. In one application, I've programmed the software to make the Boe-Bot chase the beam of a flashlight pointed a few inches in front of it. When the CPU gets an input from the right sensor that there is more light than is coming from the left sensor, it then sends output signals to the wheels to make the robot turn towards the source of the light and then move forward. Similarly, your cars' CPU takes input data from sensors, then uses tables in the software to determine the appropriate output to make your car function as required. An example of this relates to idle speed in the summer, when you have the air conditioning on. The air conditioning compressor is typically a belt run device, and when it is activated can require an enormous amount of energy to run. This bogs the engine down and reduces engine speed. If there were no way to compensate for this added drag on the engine, the car may die, or at least run badly. When an input signal is recieved from the input sensor, the CPU knows that the air conditioning compressor has been turned on. It then uses tables in the software to look up output data based on all sensor input information under current conditions. An output signal is made to some engine control device to raise idle in order to maintain optimum speed. I'm sure it's easy to see why I'm so interested in electronics, and how closely this extracurricular activity matches the vehicles I work on daily. I hope that I've been able to open a little gateway into the operation of your car, and remove a little bit of the mysticism of how it works.