pdf file dtmf based home automation using atmega16

[jaseela123d]

Generally, appliances used in our home are controlled with the help of switches. These days, you can see many technologies used in home automation projects. His article presents the control of the appliances through the DTMF technology. 

DTMF is the acronym for Dual Tone Multi Frequency. So, just think when you make the call for customer care, you will be asked to press 1, 2 or any other number. When you press a number on your mobile, a particular action is happening. All this is due to DTMF. When you press a button on your mobile keyboard, it will generate a two-frequency tone. These tones are called row and column frequencies.

Required components

DTMF based on the home automation system that controls the circuit consists mainly of the following components:

• ATmega8 Microcontroller

• HT9107BIC

• Relay

• AC Charging

• Crystal Oscillator

• Resistors

• Capacitors

The IC of the decoder consists of a built-in top amplifier, and to separate the low and high frequencies, the output of an operational amplifier is given to the pre filters. And then, it is passed through the code detector and frequency circuits, so the 4 bit binary code is locked. The tone generated from the mobile is sent to the operational amplifier via the capacitor and the DTMF resistance on pin1.

• Here, pin1 is a non-inverting pin, which is connected to pin4 which is Vref.

• Pin3 is the output of the operational amplifier, which is the feedback to pin2 using a 100Kohm resistor.

• Pin7 and pin8 are connected to the crystal oscillator.

• Pin15 is a valid data pin. When a DTMF tone is detected, this pin becomes loud.

• The procedure of the frequency detection signal to be digitized is made by a steering circuit consisting of 10k resistor, capacitor, RT / GT and EST.

• Pin11 and Pin14 are DTMF output pins that are connected to pins PB0 to PB3 of the controller.

• PD0 and PD1 are controller output pins that are connected to the relay. The relay output is connected to different sources such as fan, light, etc.

Working circuit

When the circuit of DTMF controlled appliances is powered, the controller continuously checks the inputs. When 1 is pressed from the DTMF or the mobile keyboard, the IC decoder decodes the tone and generates 1 (0001), which is given to the ATmega8 microcontroller, which in turn generates a high output on the pin PD0 and is connected to a relay . Here, the relay is used to switch the circuit and therefore the light is turned on. If the received output is 2, then the light will turn off. In the same way, if the input received is 3, then the fan will turn on and if it is 4, the fan will be turned off.