|MadSci Network: Engineering|
Hi Katherine! Basically, there are two type of keyless entry systems in common use. One uses a radio signal, the other has a series of numbered buttons on the car door. Let's concentrate on the former; the radio signal. The small keypad (people usually attach them to their keychains) has a button which, when pressed, activates a small radio transmitter, not unlike a radio station sending out the latest "Back Street Boys" recording. Just as you tune your radio receiver to a station of your choosing, a receiver in your car is tuned to the particular transmitting frequency of your sending unit. When the receiver "hears" the transmitter, it activates a special circuit which activates a solenoid attached to the locking/unlocking mechaninism of the door. A solenoid is basically an circular electromagnet, in the center of which is an iron core which moves either in or out, depending on the polarity of the voltage applied to the electromagnet. But, wait a minute! What if someone else has a transmitter that sends out the same frequency signal? Wouldn't it also open your car's doors? Yup. But those guys took care of that problem. Just as you favorite radio station sends out a signal at a very specific frequency, it then "modulates" it with the "Back Street Boys" song. Your little transmitter does the same thing except, rather than using the "Back Street Boys", it modulates the signal with a digital "code", a very specific pattern of ones and zeros. The receiver in your car is set up to respond to only that particular pattern of ones and zeros, and will ignore all other codes that someone elses transmitter might send out. Usually there are about 64 thousand different codes that could be used, so the chances of someone in your area having the same code are pretty small. Also, the frequency of the transmitter must match your receiver, or it won't open the doors either! I hope this helps. Your not-so-mad scientist, Karl Kolbus KarlKolbus@ameritech.net
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