Ottawa Canada Hi Andy and list:
DTMF is a published spec. It consists of a grid of four rows and four columns. Most telephones only have the leftmost three columns, the fourth is mostly used for special functions. Each button consists of one high tone and one low tone as follows: low tones: 697, 770, 852 and 941 Hz High: 1297, 1333, 1477 and 1633 Hz (I think, am going from memory here). Example: 1 697 and 1297 2 697 and 1333 3 697 and 1477 The "A" key: 697 and 1633 4 770 and 1297 5 770 and 1333 6 770 and 1477 The "B" key: 770 and 1633 7 852 and 1297 8 852 and 1333 9 852 and 1477 The "C" key: 852 and 1633 Asterisk: 941 and 1297 Zero 941 and 1333 Octathorpe (Pound sign) 941 and 1477 The "D" key: 941 and 1633 The tolerances are plus or minus 0.5% on low tones and plus or minus 1.5% on high tones. You can find the spec in a good reference book for electrical and electronic engineers, I forget the title of one. They deliberately chose funky frequencies to avoid problems with harmonics and the chance of stray tones being received. DTMF generating chips are available and are pretty cheap or you can generate them through a sound card. If you implement DTMF generation, please include all 16 combinations,. While the 1633 column is not widely used on consumer telephones, it is widely used in ham radio and some voice mail systems for special functions. Do not confuse the a, b, c and d keys with the letters printed on numeric buttons! They are sometimes known as FO, F, I and P respectively and were originally used to identify Flash Override, Flash, Immediate and Priority telephone calls on the AutoVon telephone network for the U.S. military. Since these buttons aren't widely available on consumer telephones,, they are often used for special functions on voice mail and PBX systems, like remote programming. Hope this helps. Don't confuse DTMF with MF, the signalling scheme used on inter-office trunks and long distance circuits at one time. While both schemes use tone pairs, the tones involved are entirely different. Brian -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.405 / Virus Database: 268.11.7/438 - Release Date: 05/09/2006 ___ To leave the BrailleNote list, send a blank message to [EMAIL PROTECTED] To view the list archives or change your preferences, visit http://list.humanware.com/mailman/listinfo/braillenote
