PIC-Based DTMF Decoder
This circuit is a two-chip DTMF decoder based upon the Motorola 145436 DTMF receiver and the PIC 16C84. Audio containing the DTMF tones is fed to pin 7 of the DTMF receiver. When a pair of valid tones are received, pin 12 of the DTMF receiver goes high. This is sensed by the 16C84, which reads the code corresponding to the received tone pair from the DTMF receiver, converts it to an ASCII code, and shows the received code on the display.
The display is a 16×1 LCD. If enough tones to fill the display are received, reception of the next tone pair causes the displayed codes to be shifted to the left and the new code is displayed on the far right. Pressing switch S1 blanks the display and prepares it to receive a new set of codes.
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