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by Lior Elia on April 18th, 2004

Lior Elia

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Why do telephone dials have # and * on them and not other symbols?

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  • by redpen on April 23rd, 2004

    redpen

    This is due to beginning economics of the dial themselves. When telephones first went to touch pads, away from the old rotary dials, they used a Matrix style touch pad. The internals of this touch pad were connected where you had 1-2-3 across in the matrix, and a-b-c-d down the matrix. These then went to a tone generator in the circuitry. with 1, 2, 3, a, b, c, and d having all distinct frequency tones. They then mixed the tones. A convolution, or merging of the tones resulted. So if you pressed 1, you actually got the mixture of tones 1 and a, and the number 6 would give you the convolution of 2 and b, etc, etc.

    But this gave you 12 different tones that you could produce from this setup. At that time, all they needed were 10 tones for the numbers. They really didn't have actual uses for the 11th, and 12 tones, and they just represented them as # and *... They figured these symbols could logically represent future features not yet thought up. Some strange meeting of the minds determined they liked # and * above % and &. They could have added another row or column, giving either 15 or 16 different combinations, but they didn't even have uses at the time for the two extra, why bother with 6 or 7 extra? This just added cost, and at that time, we rented the phones... We couldn't buy them, and there were few choices from MaBell. Beige or Black pretty much wrapped it up. She had no reason to add cost to phone production. The original # and * were useless.

    The touchpad phone is a MaBell creation, who were the original loving monopoly of the phone system. The 12 tone keypad will continue to be the standard to assure backward compatibility with tone sensors around the world. They will just add buttons separate from the 12 key pad for future upgrades. Until a complete overhaul of the entire worldwide phone system, we will continue to enjoy # and * on a 12 key pad centered, and other buttons elsewhere for new features on the phone. The tone generator mandates this.

    Comments

    • Does not really focus on the main question - why * and # ?

      Lior Elia

      by Lior Elia on April 29th, 2004

    • I enjoyed reading this answer.

      Thommy

      by Thommy on August 18th, 2004

    • Lior, read the 4th sentence in the 2nd paragraph. They chose those symbols simply because they WANTED to.

      Jack Scotty

      by Jack Scotty on February 21st, 2005

    • There is a 4th column in the DTMF sequence.  16 possible keys.  It's not hooked up in consumer phones, but it is there.

      Anonymous

      by Anonymous on April 17th, 2005

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