193. In modern car alarm systems, people can start the engine with a push of a button from a remote. How is this done?
This question has a long answer, because there's lots going on. First, there is a radio transmission from the key chain to the car when you push the button. That transmission is carefully encoded so that no one else can trigger your car (the car's receiver checks for the proper authorization code when it receives the radio transmission). I won't describe the transmission/reception process in detail, because that's a whole story in its self. The receiver than activates the car's electric system, which was cut off when the driver last turned off the car. The electric system is now ready to provide sparks at the proper moments when the engine turns. Finally, the receiver starts the engine turning by activating the starter motor. An electromagnetic solenoid (a coil of wire with a piece of iron inside) pushes the starter motor or a gear from the starter motor against the car's flywheel (a huge gear attached to the engine's crankshaft) and power is supplied to the starter motor. The motor begins turning and it turns the engine. The electric system provides sparks and the engine starts up.