Author Topic: DTMF  (Read 4096 times)

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Offline Handmixer.comTopic starter

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« on: November 08, 2006, 08:25:13 PM »
Does anybody know ho to use the motorola MC145436 DTMF decoder chip? I have got the data sheet, but it isn't very useful.

Offline Militoy

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« Reply #1 on: November 14, 2006, 03:46:10 PM »
What specific info are you looking for? The chip is a basic DTMF receiver, similar to the SSI-202. You have to connect a color burst crystal (3.58 MHz) in parallel with a 1 Megohm resistor between pins 9 and 10 (X2, X1). Pin 6 (Xen) is pulled high to enable the oscillator. When a tone is detected on pin 7 (IN), pin 12 (DV) goes high. Pin 5 (GT) sets the guard time 0=short; 1=long. I think this is mostly important if there are also voice signals on your input data line. Output is 4-bit hex code, on pins 2,1,14 and 13 (D1, D2, D4, D8 respectively). Howard Sams has a pretty good book covering the subject: “Understanding Telephone Electronics”. If you’re planning to actually connect to a phone line for your keypad tones, you’ll have to connect through a DAA, to stay within FCC Part 68 rules.

Offline Admin

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« Reply #2 on: November 14, 2006, 05:36:07 PM »
to stay within FCC Part 68 rules

probably not a big deal for you but . . . the FCC has this provision that lets you break some of its rules on the grounds that:

A) your project is experimental only, meaning not a commercial product
B) it occurs over a short period of time
C) to the best of your ability you have determined that the resulting interference will have a very low possibility of causing harm

i think i got that right . . .
i think you may need a technician class license too . . . dont remember . . .


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