Date: 12-17-94 (18:55) Number: 7 of 8 (Refer# NONE) To: comet.connix.com!iirg.com!thomas.icom, THOMAS ICOM From: comet.connix.com!odin, IIRG Subj: 0nntp-article-alt.2600-8061 Read: 12-19-94 (05:54) Status: PUBLIC MESSAGE (Echo) Conf: ALT.2600 (18) Read Type: GENERAL (+) Path: csc.canberra.edu.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!msunew s!agate!howland.reston.ans.net!EU.net!dkuug!eunet.no!nuug!nac.no!trane.uninett. no!astfgl.edb.tih.no!colargol.edb.tih.no!bardj From: bardj@colargol.edb.tih.no (Baard Johannessen) Newsgroups: alt.2600 Subject: Build Your own DTMF-decoder. Date: 12 Dec 1994 04:55:59 GMT Organization: Sor-Trondelag College, Norway Lines: 50 Message-ID: <3cgl4v$peb@astfgl.edb.tih.no> NNTP-Posting-Host: colargol.edb.tih.no X-Newsreader: TIN [version 1.2 PL2] Got a few requests for details on a DTMF-decoder, so; Here's how to use the 'MT 8870 B' DTMF-decoder: +5V ----------------------------------------------------O--------0 | | | | | === 100nF MT8870B | | --------- --------- | | 1 | |_| | 18 | | O--{] IN+ VDD [}----O | | 2 | | 17 | | 0----/\/\/\-O--------|--{] IN- St/GT [}----|--------O 100K | | 3 | | 16 | | O-/\/\/\-|--{] GS ESt [}----|-/\/\/\-O 100K | 4 | | 15 | 300K O--{] Vref StD [}----|--------------------0 5 | | 14 | O----------------{] IC Q4 [}----|--------------------0 | 6 | | 13 | O----------------{] IC Q3 [}----|--------------------0 | 7 | | 12 | | O---|[]|---{] OSC 1 Q2 [}----|--------------------0 | | 3.58MHz8 | | 11 | | O----------{] OSC 2 Q1 [}----|--------------------0 | 9 | | 10 | O----------------{] VSS TOE [}----O | | | | --------------------- | __|__ ////// GND V-DD = +5V I-typ = 3mA All resistors are +/- 1% All capacitors are +/- 5% I have taken this design from a book, and never used it myself, so if You have any questions about it, I probably woun't be able to answer them. -- Baard Johannessen - bardj@colargol.edb.tih.no - baard.johannessen@dasan.thcave.bbs.no .