Adopt the dialing demoder conceptual design of embedded DTMF of MSP430

  
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DTMF dual tone multifrequency The signal is a commonly used signalling in the telephone network, no matter on home telephones, cellular telephones or SPC exchanges, adopt DTMF signal transmission receiving numbers more. DTMF technology can also be used for occasions such as power line carrier communication, etc. It is obvious, DTMF has extensive ap
Adopt the dialing demoder conceptual design of embedded DTMF of MSP430 - schematic

plication to dial and decode in communication system and others. Usually the detection of DTMF signal is realized by special purpose chip or DSP, but its great of cost. This text has introduced a kind of low-cost DTMF dialing demoder based on MSP430F133 and realized the scheme. MSP430F133 one 16 the intersection of RISC and the intersection of structure and MCU of TI, most short instruction cycle 150ns, contain 8KB Flash ROM, 256B RAM and built-in 12 ADC. DTMF to amount to 16 character 0~9, A on the dial plate D and * / E, # / F in signal, come on a encoder mode that show with 8 frequency of audiorange. 8 frequency divide into high-frequency cluster and the intersection of low frequency and the intersection of cluster and two set, respectively as list frequently and horizontal frequency. Each signal of character come from list frequently and two superposition of signal of sine of frequency of horizontal frequency. The mode of combination of the frequency is shown as in Fig. 1. Propose, the technical indicator of DTMF signal is according to CCITT Q. 23: Convey / 10 numbers per second, or each number 100ms in receiving ratio. Each number is conveyed in the course, signal at least 45ms of existence time, and does not exceed 55ms, other time of 100ms are the squelch muting. Allow not to exceed 1. 5% of the frequency errors of in each frequency is clicked. Any exceeds 3. 5% of the signals of of given frequency, is considered...



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