30 min

Detect DTMF tones accurately and effortlessly with MT8870D and PIC32MX764F128L

Revolutionizing tone decoding: Unveiling the ultimate DTMF receiver

DTMF Decoder Click with Fusion for PIC32 v8

Published Oct 22, 2023

Click board™

DTMF Decoder Click

Development board

Fusion for PIC32 v8


NECTO Studio



Explore the cutting-edge DTMF receiver that seamlessly combines band-split filtering and digital decoding, enabling the detection and decoding of all 16 DTMF tone-pairs into a 4-bit code



Hardware Overview

How does it work?

DTMF Decoder Click is based on the MT8870D, an integrated DTMF receiver with enhanced sensitivity from Microchip Technology. It offers low power consumption and high performance. It consists of a band split filter section separating the high and low group tones, followed by a digital counting section that verifies the received tones' frequency and duration before passing the corresponding code to the output bus. This Click board™ has two ways to detect tones: a mobile phone with a 3.5mm jack, which provides the DTMF signals to the MT8870D decoder, or an onboard microphone to listen to the DTMF tones generated by the cell phone. The MT8870D uses digital counting techniques to detect and decode all 16 DTMF tone-pairs into a 4-bit code. DTMF

Decoder Click communicates with MCU using a standard I2C 2-Wire interface, with a clock frequency up to 100kHz in the Standard and 400kHz in the Fast Mode. Using the PCA9536 port expander that communicates with the MCU via I2C communication, it is possible to display visually, in binary form, the digit of the pressed number. The digit in binary form is then visually displayed using four red LEDs, labeled from Q1 to Q4, in the board's upper right corner. This Click board™ also has a power-down feature routed on the CS pin of the mikroBUS™ socket labeled as PWD. A logic high applied to pin PWD will power down the device to minimize the power consumption in a Standby mode, which stops the oscillator and the filters' functions. Also, it uses the

interrupt pin of the mikroBUS™ labeled as STD with an additional LED indicator signaling that a received tone pair has been registered, and the INH pin, which inhibits the detection of tones representing characters A, B, C, and D. The output code will remain the same as the previously detected code. This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the VCC SEL jumper. This way, both 3.3V and 5V capable MCUs can use the communication lines properly. Also, this Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used as a reference for further development.

DTMF Decoder Click hardware overview image

Features overview

Development board

Fusion for PIC32 v8 is a development board specially designed for the needs of rapid development of embedded applications. It supports a wide range of Microchip's PIC32 microcontrollers regardless of their number of pins and a broad set of unique functions, such as the first-ever embedded debugger/programmer over WiFi. The development board is well organized and designed so that the end-user has all the necessary elements, such as switches, buttons, indicators, connectors, and others, in one place. Thanks to innovative manufacturing technology, Fusion for PIC32 v8 provides a fluid and immersive working experience, allowing access anywhere and under any circumstances at any time. Each part of the

Fusion for PIC32 v8 development board contains the components necessary for the most efficient operation of the same board. In addition to the advanced integrated CODEGRIP programmer/debugger module, which offers many valuable programming/debugging options and seamless integration with the Mikroe software environment, the board also includes a clean and regulated power supply module for the development board. It can use a wide range of external power sources, including a battery, an external 12V power supply, and a power source via the USB Type-C (USB-C) connector. Communication options such as USB-UART, USB HOST/DEVICE, CAN (on the MCU card, if

supported), and Ethernet is also included. In addition, it also has the well-established mikroBUS™ standard, a standardized socket for the MCU card (SiBRAIN standard), and two display options for the TFT board line of products and character-based LCD. Fusion for PIC32 v8 is an integral part of the Mikroe ecosystem for rapid development. Natively supported by Mikroe software tools, it covers many aspects of prototyping and development thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.

Fusion for PIC32 v8 horizontal image

Microcontroller Overview

MCU Card / MCU



8th Generation



MCU Memory (KB)


Silicon Vendor


Pin count


RAM (Bytes)


Used MCU Pins

mikroBUS™ mapper

Inhibit Mode
Power Down Mode
Power Supply
New Tone Indicator
I2C Clock
I2C Data
Power Supply

Take a closer look


DTMF Decoder Click Schematic schematic

Step by step

Project assembly

Fusion for PIC v8 front image hardware assembly

Start by selecting your development board and Click board™. Begin with the Fusion for PIC32 v8 as your development board.

Fusion for PIC v8 front image hardware assembly
GNSS2 Click front image hardware assembly
SiBRAIN for PIC32MZ1024EFK144 front image hardware assembly
GNSS2 Click complete accessories setup image hardware assembly
v8 SiBRAIN Access MB 1 - upright/background hardware assembly
Necto image step 2 hardware assembly
Necto image step 3 hardware assembly
Necto image step 4 hardware assembly
NECTO Compiler Selection Step Image hardware assembly
NECTO Output Selection Step Image hardware assembly
Necto image step 6 hardware assembly
Necto image step 7 hardware assembly
Necto image step 8 hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Necto PreFlash Image hardware assembly

Track your results in real time

Application Output

After pressing the "FLASH" button on the left-side panel, it is necessary to open the UART terminal to display the achieved results. By clicking on the Tools icon in the right-hand panel, multiple different functions are displayed, among which is the UART Terminal. Click on the offered "UART Terminal" icon.

UART Application Output Step 1

Once the UART terminal is opened, the window takes on a new form. At the top of the tab are two buttons, one for adjusting the parameters of the UART terminal and the other for connecting the UART terminal. The tab's lower part is reserved for displaying the achieved results. Before connecting, the terminal has a Disconnected status, indicating that the terminal is not yet active. Before connecting, it is necessary to check the set parameters of the UART terminal. Click on the "OPTIONS" button.

UART Application Output Step 2

In the newly opened UART Terminal Options field, we check if the terminal settings are correct, such as the set port and the Baud rate of UART communication. If the data is not displayed properly, it is possible that the Baud rate value is not set correctly and needs to be adjusted to 115200. If all the parameters are set correctly, click on "CONFIGURE".

UART Application Output Step 3

The next step is to click on the "CONNECT" button, after which the terminal status changes from Disconnected to Connected in green, and the data is displayed in the Received data field.

UART Application Output Step 4

Software Support

Library Description

This library contains API for DTMF Decoder Click driver.

Key functions:

  • dtmfdecoder_tone_read - This function reads a last registered tone and returns decoded data in character format

  • dtmfdecoder_delayed_steering_check - This function checks the state of the StD pin

  • dtmfdecoder_powerdown_off - This function powers up the device and along with the oscillator

Open Source

Code example

This example can be found in NECTO Studio. Feel free to download the code, or you can copy the code below.

 * @file main.c
 * @brief DTMFDecoder Click example
 * # Description
 * This example shows the basic tone capture of
 * DTMF frequencies, decoding and representing
 * them on the UART LOG.
 * The demo application is composed of two sections :
 * ## Application Init
 * Initializes I2C and UART LOG drivers and powers
 * on the device.
 * ## Application Task
 * Checks the delayed steering for incoming tones
 * and decoding them on the UART LOG. Holding the
 * same key will recognize multiple tone generation,
 * the tone register delay constant can be set to
 * adjust the tolerance.
 * @author Stefan Nikolic

#include "board.h"
#include "log.h"
#include "dtmfdecoder.h"

static dtmfdecoder_t dtmfdecoder;
static log_t logger;

static const uint16_t tone_register_delay = 200;

void application_init ( void ) {
    log_cfg_t log_cfg;                  /**< Logger config object. */
    dtmfdecoder_cfg_t dtmfdecoder_cfg;  /**< Click config object. */

     * Logger initialization.
     * Default baud rate: 115200
     * Default log level: LOG_LEVEL_DEBUG
     * @note If USB_UART_RX and USB_UART_TX 
     * are defined as HAL_PIN_NC, you will 
     * need to define them manually for log to work. 
     * See @b LOG_MAP_USB_UART macro definition for detailed explanation.
    LOG_MAP_USB_UART( log_cfg );
    log_init( &logger, &log_cfg );
    log_info( &logger, " Application Init " );

    // Click initialization.

    dtmfdecoder_cfg_setup( &dtmfdecoder_cfg );
    DTMFDECODER_MAP_MIKROBUS( dtmfdecoder_cfg, MIKROBUS_1 );
    err_t init_flag = dtmfdecoder_init( &dtmfdecoder, &dtmfdecoder_cfg );
    if ( init_flag == I2C_MASTER_ERROR ) {
        log_error( &logger, " Application Init Error. " );
        log_info( &logger, " Please, run program again... " );

        for ( ; ; );

    dtmfdecoder_default_cfg ( &dtmfdecoder );
    Delay_ms( 100 );
    log_info( &logger, " Application Task " );

void application_task ( void ) {
    uint8_t result;
    if ( dtmfdecoder_delayed_steering_check( &dtmfdecoder ) ) {
        result = dtmfdecoder_tone_read( &dtmfdecoder );
        log_printf( &logger, " Detected key tone:\t%c\r\n", result );
        Delay_ms( tone_register_delay );

void main ( void ) {
    application_init( );

    for ( ; ; ) {
        application_task( );

// ------------------------------------------------------------------------ END

Additional Support