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Speaker 1: stuff works dot com where smart Happens. Hi Am Marshall
Speaker 1: Brain with today's question, how does collar i D work?
Speaker 1: If you have a color i D box attached to
Speaker 1: your phone, or if the color i D box is
Speaker 1: built into your phone, or if you have a cell phone,
Speaker 1: then an amazing thing happens. Every time your phone rings,
Speaker 1: the number, and sometimes even the name of the calling
Speaker 1: party appears on the display right after the first ring.
Speaker 1: It turns out that the process of making the color
Speaker 1: i D display possible is remarkably simple at your end
Speaker 1: of the line. If you've read the house stuff Work
Speaker 1: article entitled how modems work, then you know that the
Speaker 1: early modems used a technique called frequency shift keying to
Speaker 1: transmit bits over the phone line. Frequency shift keying is
Speaker 1: extremely simple. One tone, for example, like twelve hundred hurts
Speaker 1: or beep represents a one, and another tone LIKEEP represents
Speaker 1: a binary zero. A modem changes frequencies depending on whether
Speaker 1: it wants to send a one or a zero. How
Speaker 1: quickly it changes frequencies determines the speed or the bod
Speaker 1: rate of the modem. To send caller i D information
Speaker 1: to your home, the phone company uses a frequency shift
Speaker 1: keying technique identical to a two modem from a million
Speaker 1: years ago, and it sends asky character data to the phone.
Speaker 1: The modem message is sent between the first and the
Speaker 1: second ring, so the phone rings once and if you
Speaker 1: could listen to the phone line just after that ring,
Speaker 1: you would hear bleep sound about half a second long,
Speaker 1: and if you decoded the bleep, you would find that
Speaker 1: it contains first a series of alternating ones and zeros
Speaker 1: to help the caller i D box get the timing down,
Speaker 1: then a series of a hundred and eighty ones, and
Speaker 1: then a bite representing the type of message that's about
Speaker 1: to be sent, and then a bite representing the length
Speaker 1: of the message, then a pair of bites representing the month, day, hour,
Speaker 1: and minute that the message was sent, and then the
Speaker 1: tendiget phone number in ten bytes, followed by a checksum
Speaker 1: bite so the phone can make sure the message came
Speaker 1: through okay. There's also a more advanced system that contains
Speaker 1: the caller's name, but its technique is identical. Each character
Speaker 1: is sent with a standard eight bit asky character, preceded
Speaker 1: by a zero start bit and followed by a one
Speaker 1: stop bit. The phone contained the twod modem to decode
Speaker 1: the bits, a little circuit to detect the ringing signal,
Speaker 1: and a simple processor to drive the display. That's really
Speaker 1: all the into the whole thing. For more on this
Speaker 1: and thousands of other topics, visit how staff works dot com.
Speaker 1: Audible dot com is the leading provider of digital audio
Speaker 1: books and spoken word, with over one thousand titles to
Speaker 1: choose from. Audible lets you listen to your favorite books anywhere, anytime.
Speaker 1: Go to audible podcast dot com slash stuff brain to
Speaker 1: get a free audio book download of your choice when
Speaker 1: you sign up today.