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DTMF Interfacing 8051 Microcontroller

 

DTMF Interfacing 8051 Microcontroller Family Models :
Atmel, NXP, Philips, 8051, 8052, 89C51, 89C52, 89S51, 89s52, 89C1051, 89C1051, 89C2051, AT89C4051, AT89S8252,l AT89C1051, AT89C2051, AT89C4051, P89C51RB+, P89C51RC+, P89C51RD+, P89C51RB2Hxx, P89C51RC2Hxx, P89C51RD2Hxx, P89C660, P89C662, P89C664, P89C668, P89C669, P89C51RA2xx, P89C51RB2xx, P89C51RC2xx, P89C51RD2xx, P89C60X2, P89C61X2,P89LV51RB2, P89LV51RC2, P89LV51RD2, P89V51RB2, P89V51RC2, P89V51RD2, P89V660, P89V662, P89V664.
 
Introduction DTMF :  8051 Microcontroller
Dual-tone multi-frequency DTMF frequency signals are used for telecommunication. This tutorial will explain how to use Dual Tone Multi Frequency (DTMF) tones to use and interface in telecommunication. Dual Tone Multi-Frequency (DTMF) is a touch tone system used for choosing menu options in communication with an automated call handling service. Tones can only be sent over an active and connected voice calls. The caller does not need a handle to the specific call. The telephony system can send the tones over the voice calls that are connected. DTMF (Dual Tone Multiple Frequency) application is associated with digital telephony, and provides two selected output frequencies (one high band, one low band) for a du- ration of 100 ms. A benchmark subroutine has been written for the COP820C/840C microcontrollers, and is outlined in
detail in this application note. This DTMF subroutine takes 110 bytes of COP820C/840C code, consisting of 78 bytes of program code and 32 bytes of ROM table. The timings in this DTMF subroutine are based on a 20 MHz COP820C/840C clock, giving an instruction cycle time of 1 ms.
 
About DTMF IC 8870  - Dual Tone Multi Frequency
About DTMF IC 8870  - Dual Tone Multi Frequency
The M-8870 is a full DTMF Receiver that integrates both band split filter and decoder functions into a single 18-pin DIP or SOIC package. Manufactured using CMOS process technology, the M-8870 offers low power consumption (35 mW max) and precise data handling. Its filter section uses switched capacitor technology for both the high and low group filters and for dial tone rejection. Its decoder uses digital counting techniques to detect and decode all 16 DTMF tone pairs into a 4-bit code. External component count is minimized by provision of an on-chip differential input amplifier, clock generator, and latched tri-state interface bus. Minimal external components required include a low-cost 3.579545 MHz color burst crystal, a timing resistor, and a timing capacitor. An MT8870 series DTMF decoder is used here. All types of the MT8870 series use digital counting techniques to detect and decode all the 16 DTMF tone pairs into a 4-bit code output. The built-in dial tone rejection circuit eliminates the need for pre-filtering. When the input  signal given at pin 2 (IN-) in single-ended input configuration is recognized to be effective, the correct 4-bit decode signal of the DTMF tone is transferred to Q1 (pin 11) through Q4 (pin 14) outputs
 
Interfacing DTMF 8870 IC 8051 Microcontroller
In Interfacing DTMF 8870 is very simple but is should be done with proper care about the circuit designing.
Here wil will discuss simple project of caller id with 8051 Microcontroller. This Project can be used in home, shops, offices. This keep an eye on every incoming number on the selected telephone line. Basically it is the built in caller id system. When telephone rings it displays the telephone number on the LCD screen attached with the circuit. 8051 Microcontroller is responsible for every operation in the given project from controlling DTMF IC and LCD.
 
DTMF decoder ic 8870 here we are using in our project for designing Caller ID system. It's very simple circuit using DTMF decoder MT8870 (or CM8870). As shown here. When incoming call comes it interrupts the microcontroller and microcontroller decodes the number and display it on the microcontroller. In our circuit output of DTMF is connected to INT of the microcontroller which is the interrupt service routine. DTMF is functions in such a way that when incoming call comes the pins of 8870 from 11-14 are activated and tells the incoming numbers. Microcontroller is direct connected with these pins. So Microcontroller gets the incoming number and process for displaying on the LCD screen.
 
DTMF decoder ic 8870