You’d then move your finger away and the dial would slowly rotate back to its starting position. To dial a number, you’d insert your finger into the rotary dial hole for a specific number and pull the dial until your finger hit the metal bar. This rotary dial had 10 holes arranged in a circle, with each hole corresponding to a specific number-usually, “1” through “9” and followed by a “0.” The dial also had a small metal bar on one side of the circle. These wired connections also ended up having a secondary use: allowing a phone user to directly dial a telephone number from his phone, at first by using a rotary dial on the front face of the phone. (Check out our blog post on VoIP vs Landline vs Cell Calls if you’d like to learn more.) This is what enabled telephone calls to occur. Before DTMF: Rotary Dial Phones and Pulse DialingĪt the time of their first arrival in homes, telephones were physically connected to a local telephone exchange building through wires that left a phone’s handset and ended at the exchange. In this blog post, we’re focusing on one of those acronyms: DTMF, which stands for dual-tone multi-frequency signaling. When you press the digit 1 on the keypad, you generate the tones 1209 Hz and 697 Hz.You’d be excused for thinking that these letters are what you’d find when you dip your spoon into some alphabet soup, but they actually refer to some important telephone technology! The telephone world is full of these acronyms, and while you may not know what they stand for or how they work, they play a big role in our daily lives. The telephone company’s “Central Office” equipment knows what numbers you are dialing by these tones, and will switch your call accordingly. One tone is generated from a High DTMF frequency group of tones and the other from Low DTMF frequency group. 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. Users can also buy Arduino based DTMF kit from Robo India Shop: įor 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”. Users can buy this device online from Robo India Shop:

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

Dual tone multi frequency