In general, controlling of the home appliances can be done by normal switches. But, these days we frequently see the home automation for controlling the appliances using several technologies. This article presents the DTMF based load control system. DTMF is a signaling system for recognizing the inputs on a keypad. It is used in signaling for telecommunication over analog telephone lines in the voice frequency band among telephone handsets and communication devices. This Article discusses about DTMF based load control system.
Dual Tone Multi Frequency Based Load Control System
DTMF based load control system mainly uses a DTMF to control a load system, block diagram working and applications are discussed below.
What is a DTMF?
The short term of the Dual Tone Multi Frequency is DTMF. So, when you make a call to a customer care, they will inquire you to press any number on the keypad. When you push any button from your cell phone, one specific act takes place due to DTMF (dual tone multi frequency). When a button on the mobile keypad is pressed, the act instantly produces a tone of dual frequencies which are named as a column and row frequencies.
Here, in the above depicted figure, the column frequencies are high frequencies, and the row frequencies are low frequencies. These row and column frequencies are selected for DTMF in such a way that they don’t have a harmonic relation with the others. As a result, they will not produce similar tones. The row frequencies are a bit lower than the column frequencies.
DTMF Decoder Circuit
The DTMF decoder circuit is inbuilt with an operational amplifier and to divide low &high frequencies, the o/p of an op-amp is known to the pre-filters. And it passed though the code detector & frequency circuits. The generated mobile tone is sent through the resistor and a capacitor of the DTMF.
- A non inverting pin pin-1 is connected to the pin 4.
- The output of an op-Amp is the Pin-3 which is given as a feedback to the pin-2.
- The pin-7 & pin-8 is connected to the both the pins of a crystal oscillator.
- Pin-15 is the data interconnection pin.
- The o/p pins Pin-11 & 12 are connected to DTMF pins, then it is connected to relay.
- The o/p of the relay connected to pb0 & pb3 pins of the microcontroller.
- The o/p pins PD0 & PD1 of the controller are connected to the relays.
- The o/p of the Relay is connected to the load.
The hardware and software requirements mainly include; 8051 series Microcontroller, Transformer, DTMF Decoder, Relays, Relay Driver IC, Inverter IC, Voltage Regulator, Crystal, Diodes, Resistors, Capacitors, Lamps., Kiel compiler and Languages: Embedded C programming language or Assembly
The proposed system works on the basic concept of a DTMF tone signal received from any mobile to operate remotely for controlling any loads like domestic loads, agricultural pump and industrial loads, etc.
In many industries, the different loads occupy over a large area and therefore, operating of these loads can be tiresome and also difficult task. In the field of agricultural also, water pumps and other loads are connected over a huge area and thus it is not easy for the planter to activate all the loads and likewise for household loads. Keeping these troubles in mind, this project has been designed that uses DTMF technology to manage the loads remotely.
A cell phone is connected to a dual tone multi frequency decoder in the system from the output of an audio socket for getting toned instructions. The receiving codes are changed into digital commands by using a DTMF Decoder which will recognize the frequency of the cell phone key and change that frequency to its equal digital code which is then fed to a 8051 family microcontroller.
As per the instructions sent from the mobile of the sender, the microcontroller will send instructions through a buffer to activate the individual loads by switching the relays ON/OFF. These relays are triggered by a relay driver IC connected to the microcontroller.
Further, the proposed system can be improved by using a GSM modem, where the different loads can be restricted by sending an SMS. This will reduce the require of answering the call for the system to work.
Advantages and Applications
- Using this Dual Tone Multi Frequency the loads can be operated from anywhere
- The applications of dual tone multi frequency mainly include industries, home, agriculture, etc.
- The DTMF tones are used to at the telephone switch centers for finding of calls or dialled number. These are used by a particular cable network
- These networks employ DTMF tones to indicate a local cable operator or network station when a local ad is to be put in. In distribution, this is known as local placing. DTMF tones were also used by global stations for switching on & off remote transmitters
Thus, this is all about dual tone multi frequency based load control system. We hope that you have got a better understanding of this concept or electrical and electronic projects, please give your valuable suggestions by commenting in the comment section below. Here is a question for you, what is the main function of DTMF?