Single audio decoding circuit diagram

The single tone decoding circuit is shown in the figure, which is a circuit for a dual tone multi-frequency (DTMF) decoder. The DTMF modulated signal sent from the outside is led to seven single-tone narrow-band filters composed of the integrated circuit LM567 with center frequencies of 697~1447Hz, and then sent to the NAND gate in pairs to output the corresponding 1, 2,... , 9, 0 and other numbers.

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