This project is a DTMF decoder running on a NUCLEO-F072RB board.
Reads analog input from PA0 and prints decoded code on UART2 @115200, 8N1.
OUT1 output signal is driven low when DTMF key 1 is detected and is driven high when key 2 is detected.
Same goes with OUT2 signal when keys 4 and 5 are detected. This is useful for driving, for example, a relay for remote automation purposes. See for example isolated relay board
The software is easily portable to any other STM32 device as STM32 Cube libraries are used.
The DTMF decoding is taken from an old ARM Keil project based on STM32F103 and SPL libraries.
Pinout
| Signal | STM32 IO | Nucleo connector |
|---|---|---|
| ADC input | PA0 | CN7-28 |
| OUT1 | PC2 | CN7-35 |
| OUT2 | PC3 | CN7-37 |
| 8kHz TIM DBG | PC4 | CN10-34 |
| DMA CPLT DBG | PB13 | CN10-30 |
Note: as ADC only reads positive voltage values, audio input signal should be conditioned so to add DC offset to ADC input. See, for example:
https://electronics.stackexchange.com/questions/14404/dc-biasing-audio-signal https://electronics.stackexchange.com/questions/5315/how-to-read-an-audio-signal-using-atmega328
Can also be used without signal conditioning but some keys won't be recongnized. Keys 1, 2, 4, and 5 have been successfully tested without applying DC offset.