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