This tutorial explains the working of DTMF module (by Robo India).

Step 1: Introduction:

DTMF stands for “Dual Tone Multi Frequency”, and is a method of
representing digits with tone frequencies, in order to transmit them over an analog communications network.

We have use DTMF module (by Robo India) in this tutorial.

Users can buy this device online from Robo India Shop: https://roboindia.com/store/dtmf-controller

Users can also buy Arduino based DTMF kit from Robo India Shop:https://roboindia.com/store/dtmf-automation-aruduino-kit

For example telephone line, When we dial to a customer care service and
there machine responses “Press 1 to do so”, “Press 2 to do so”. That is an application of DTMF.When you press the buttons on the keypad, a connection is made that generates two tones at the same time. One tone is generated from a High DTMF frequency group of tones and the other from Low DTMF frequency group. The telephone company’s “Central Office” equipment knows what numbers you are dialing by these tones, and will switch your call accordingly.

When you press the digit 1 on the keypad, you generate the tones 1209 Hz and 697 Hz.

Step 2: Hardware Interfacing:

Only a single cell phone is required to work with this module.
There are four LEDs on this module.

PWR and ST: Turn On when device is taking some input.

R1 and R2 : two LEDs for Relay. These LEDs display output according to pressed button.

When button 1 is pressed, R1 is turn On.

When button 2 is pressed, R2 is turn On.

When button 3 is pressed, both are turn On.

When button 4 is pressed, both are turn Off.

Step 3: DTMF Connection

To test Robo India DTMF module you need make the following circuit.

Connect your phone to DTMF module with the help of 3.5mm auxiliary cable.

Step 4: DTMF to Operate AC Devices:

DTMF can be used to operate AC device as well. In below diagram, a
bulb connected with 220V socket with one phase and from another phase it connects with NO pin of 12V Relay.

Another phase of socket is connected with Common pin of Relay. When 12V power is given to DTMF board, bulb will turn On.