The following is a re-post of something I read in sci.electronics. I believe that T.H. Tsim is the author.
Author : T.H. Tsim Version: 0.3 (draft, pre-release :-) Date : April 12, 1994 E-mail : firstname.lastname@example.org Contents: 1. Short introduction to DTMF 2. List of DTMF-receiver chips _________________________________________________________________ Hi! After reading sci.electronics for a couple of years, I've discovered that many people are interested in decoding DTMF-signals for various applications. A frequently asked question (FAQ) concerning this subject is: "What IC should I use in order to decode DTMF signals?" _________________________________________________________________ 1) Short introduction to DTMF DTMF means: Dual Tone Multiplexed Frequency, the tones you might have heard while pressing the keys on your telephone. Each key produces a slightly different signal, which is a mixture of two frequencies, i.e. pressing '1' will send a tone made of 1209 Hz and 697 Hz to the other end of the line. 1209 Hz 1336 Hz 1477 Hz 1633 Hz ABC DEF 697 Hz 1 2 3 A GHI JKL MNO 770 Hz 4 5 6 B PRS TUV WXY 852 Hz 7 8 9 C oper 941 Hz * 0 # D There are many ways to detect and decode these DTMF tones. One idea could be an eight sharp-tuned filter combination with detection circuits. Needless to say, this is very impractical, considering the various ICs (Integrated Circuits or 'chips') made by different manufacturers all over the world. Most of these ICs do not require more than one (inexpensive) 3.58 MHz x-tal or resonator and the power circuitry. Usually the output is 4-bit binary + 1 strobe. -------------- l l- d3 l DTMF l- d2 signal in -l Decoder l- d1 4-bit binary out l chip l- d0 l l- strobe -------------- Note: This figure is merely for decoration, it does not imply package information Nice text to read about DTMF and telephony can be found in: "Understanding Telephone Electronics" Howard W.Sams & Co ISBN: 0-672-27018-18 2) List of DTMF-receiver chips The companies are listed in a random order: Silicon Systems Inc. SSI202 DIP-18 SSI203 DIP-18 SSI204 DIP-14 All req. 3.58 MHz (3.579545 MHz) crystal A neat and well documented design + PCB layout by Tom Miller KA1JQW, can be found in "The ARRL handbook for radio amateurs", ISBN: 0-87259-169-7 Chrystal Semiconductor Corp. CS20x family OKI MSM6843 DIP-28, 3.58, 4b1s Application note in OKI Telecom LSI data book Motorola MC145436 MC68HC05F5 (From Arkady Horak-Systems) I spent about the last 14 months of my life working on an integrated DTMF receiver here at Motolora and I would like to have you add the part to the DTMF-list. The receiver is part of a 6805 8-bit microcontroller and is called the MC68HC05F5. Here is a quick feature list: * MC68HC05 based core micro * Memory mapped I/O registers * 5632 bytes of user ROM * 224 bytes of RAM * 15-bit multi-function timer * Power saving STOP, WAIT and Data-Retention modes * Mask optional COP (computer operating properly) or watchdog timer * Self check ROM * Fully static operation with no minimum clock speed * 30 bidirectional I/O pins * On chip oscillator for use with external crystal or ceramic resonator 2 or 4 MHz operation only while DTMF rec. is functioning * DTMF receiver * 40 pin plastic dip or 44 pin plastic leaded chip carrier packages Being an avid electronics hobbyist I feel this part will see a lot of service in hobby applications. This part is, to the best of my knowledge the first general purpose microcontroller with an integrated DTMF receiver. Currently only a ROM based version is available but as sales grow a 705 or EPROM version may be manufactured. Also, this part is compatible with the 6805 development tools and software. Arkady Horak
Motorola CSIC Microcontroller Division Austin, TX Teltone M957-0x DIP-22 or SOIC-24, 4b1s, 5 and or 12 Volt (read below) CAUTION: M957-02 and M957-01 differ in operating voltage!, M957-01 can operate from 5 - 12V, M957-02 operates 5V only (not suitable for 12 V apps!) A ready to build schematic by R.G. Krijgsman based on this Teltone M957-2 chip can be found in: "Het Elektuur telefoonboek" ISBN 90-70160-94-3, (Dutch language) Unknown KT3170 DIP-18, minimal ext. parts ? UMC, United Microelectronics Corp. UM9203 DIP-18 4b1s and 2of8 UM9204 DIP-14 UM92870A/B/C DIP-18 (three variants) Examples of line-interfaces and app-notes in the UMC communications ICs databook. Mitel Corp MV8870 Note: Teltone seem to carry this type-number as well. Toshiba TC35301AP DIP-28, 4b1s Harris CD22202 DIP-18, 4b1s CD22203 DIP-18 4b1s and 2of8 CD22204 DIP-14 or SOIC-24, 4b1s Legend: 3.58 = an inexpensive 3.58 MHz needed 4b1s = 4-bit 1 strobe output (Hexoutput) 2of8 = 2-of-8 code _________________________________________________________________
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