![]() ![]() The output of an inbuilt op-amp in the decoder IC is pin-3, the response signal is given by linking the pin3 to inverting input of pin-2 using a 270kΩ resistor. The op-amp’s non-inverting terminal is fed to pin-4, and the voltage at pin-4 is Vcc/2. ![]() The signals from the microphone pin are connected to an inverting i/p of an inbuilt operational amplifier in decoder IC through a resistor as well as a capacitor. The decoder IC M8870 includes an operational amplifier. The Decoded Output for Row and Column Frequencies Key The microphone wire signals can be processed with the decoder IC to generate a binary series as a parallel o/p such as Q1, Q2, Q3, & Q4. Here the red wire is an input of the DTMF circuit. The microphone consists of two wires namely red wire and green wire. The signals from the DTMF can be tapped straight using microphone pin in the cell phone. The required components of this circuit mainly include M8870 decoder IC, Resistors- 70kΩ, 100kΩ, and 390kΩ, two capacitors- 0.1♟, and crystal oscillator– 3.579545MHz. The bits which are decoded can be associated with a microprocessor or a computer for future application. The entire communication includes the touch tone inventor as well as a tone decoder. The tone of the DTMF is a type of one way communication among the user and the telephone exchange switch room. This IC uses a technique of digital counting for deciding the tones frequencies, as well as to confirm that they communicate to normal frequencies of DTMF. The decoder IC decodes the DTMF input to five digital outputs. This circuit can be built with a decoder IC MT8870DE for the recognition of DTMF indications. This DTMF decoder circuit recognizes the phone tone from the phone line and then decodes the pressed key on the keypad of the telephone. ![]()
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