DTMF Decoder Click Board™

How Does The DTMF Decoder Click Board™ Work?

The DTMF Decoder Click Board™ is based on the MT8870D, an integrated DTMF receiver with enhanced sensitivity from Microchip Technology. It offers low power consumption and high performance and consists of a band split filter section, which separates 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.

The DTMF Decoder Click Board™ has two ways to detect tones: with a mobile phone with a 3.5mm jack which provides the DTMF signals to MT8870D decoder, or using an onboard microphone used to listen 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.

The DTMF Decoder Click Board™ communicates with MCU using 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 visually display, in binary form, the digit of the pressed number. The digit in binary form is then visually displayed using four red LEDs, labelled from Q1 to Q4, located in the board's upper right corner.

The DTMF Decoder Click Board™ also has a power-down feature routed on the CS pin of the mikroBUS™ socket labelled 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™ labelled as STD with an additional LED indicator signaling that a received tone pair has been registered, and 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.

The DTMF Decoder Click Board™can operate with both 3.3V and 5V logic voltage levels selected via the VCC SEL jumper. This way, it is allowed for both 3.3V and 5V capable MCUs to properly use the I2C communication lines. However, the 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.

SPECIFICATIONS

PINOUT DIAGRAM

This table shows how the pinout of the DTMF Decoder Click Board™ corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).

Notes	Pin					Pin	Notes
NC	1	AN	PWM	16	NC
Inhibit Mode	INH	2	RST	INT	15	STD	New Tone Indicator
Power Down Mode	PWD	3	CS	RX	14	NC
NC	4	SCK	TX	13	NC
NC	5	MISO	SCL	12	SCL	I2C Clock
NC	6	MOSI	SDA	11	SDA	I2C Data
Power Supply	3.3V	7	3.3V	5V	10	5V	Power Supply
Ground	GND	8	GND	GND	9	GND	Ground

ONBOARD SETTINGS AND INDICATORS

DTMF DECODER CLICK ELECTRICAL SPECIFICATIONS