Many phones use a DTMF receiver is integrated . The majority of them are manufactured by companies that Motorola MT8870 is integrated . There are 18 pieces on this integrated pin . However, this is not integrated within the phones alone , can also be used in various applications . However, how to integrate the various projects that are used and it is not necessary to yield engineers and technicians felt the need to integrate these are tested separately .

This integrated laboratory and communications-related saves a lot of time in various manufacturing industries . A simple scheme is given for integrated DTMF here . This integrated DIP -18 with sheath structure that can be easily fitted on the PCB for a breadboard or can be easily installed on the circuit .

For optimum operation of telephone equipment , the DTMF receiver 40ms’ for more than a couple of tone and should be designed to recognize . However, remote controls , radio frequency , etc. working with or providing wireless communication applications . applications , creating a negative impact on the tone of the noise causes . Thus activated , additional strength and duration of the tone can be changed by adding a diode

Balanced circuit is designed in line mode . Common mode noise signals a balanced differential amplifier input to prevent use . The circuit also destroyed properly (finalized) telephone line interface provides control over the mükemel . Jump to protection resistor divider and zener diode ( ZD1 , ZD2 ) can be added . These resistors and diodes, current limiting will occur on the line provides a temporary absorption of energy .

Pressing any key on the keypad of the phone when connected via R15 to the output of the std MT8870 integrates gives LED5 light . This IC is connected to pins 16 and 17 depending upon the values ​​of resistors and capacitors will remain at a high level for a while .

Shown within the dotted lines of the material contained in the box , the time setting is used for circuit protection . LED1 connected to pins 11 and 14 of the IC … LED4 LEDs , resistors R11 through R14, respectively … are active . So the key pressed on the telephone keypad tones of the binary system is shown on the LEDs after conversion . LED1 lowest ( LSB) , LED4 highest ( MSB) bit represents .

For example, did you press the 5 key on the keypad , then to give light LED1 and LED3 ( 0101) . So for each number corresponding LEDs will light when pressed . Thus, IC, pressing the keys on the phone keypad decimal values ​​will be read as a binary value .

MT8870 DTMF Receiver with Integrated KT3170 or the circuit for testing the following ways :

1) Even a parallel phone and connect the circuit .
2) Open switch S1 .
3) Now for the * key to generate tons of press .
4) Then, press decimal .
5) Compare this with what you see in the picture table .
6) If you ‘re seeing right of the decimal figures LED4 with LED1 MT8870 DTMF is correct.

Tables A, B, C and D letters you see. They are used for a special synchronizing on a regular phone because you can not see this button. For the 5th IC pin pull-down switch S2 is made. A, B, C and D tones S2 corresponding to the character button is turned off may be formed.