DTMF ( Dualtone Multiple Frequency ) is one of the most widely used signaling in Telecom Domain. Though there are many chips available in the market for generating DTMF tones, here is an example how to generate DTMF using simple R2R ladder network and 8BIT I/O Port of an MCU.

Any MCU one I/O port should be directly connected to R2R ladder network as shown above picture. Since DTMF uses two frequencies, lower order bits ( Bit 0 to Bit 3) should be used to generate one frequency using simple SINE values, and the higher order bits (Bit 4 to Bit should be used to generate the other frequency. Both the frequency would be added up automatically and the resultant DTMF tones would be generated through output of the R2R ladder network!

Quite simple, right ? But one should be careful about timing! Here is the frequnecy table for DTMF tones
1209 Hz 1336 Hz 1477 Hz 1633 Hz
697 Hz 1 2 3 A
770 Hz 4 5 6 B
852 Hz 7 8 9 C
941 Hz * 0 # D

Using it one can easily generate DTMF tones.

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Tags: DTMF, DTMF Generation, DTMF Tone, mcu, r2r, r2r ladder network

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