Generally, several home equipment can be controlled by switches. But these days we can observe the home automation to control the appliances using various technologies. This article presents the DTMF based load control system. The term DTMF stands for Dual Tone Multi Frequency is a signalling system for recognizing the DTMF keys on a keypad. The applications of DTMF include telecommunication signalling over analogue telephone lines in the voice frequency band among telephone handsets and communication devices. So, when you make a call for customer care they will request you to push any number. When you push any number on your mobile keypad, one specific action will occur because of DTMF. When a keypad button is pressed in a mobile keypad, instantly it will produce a tone of two frequencies called column and row frequencies. Here, the column frequencies are high frequencies and row frequencies are low frequencies.
Dual Tone Multi Frequency based Load Control System
The hardware and software necessities of DTMF based load control system mainly include; 8051 series Microcontroller, DTMF Decoder, Transformer, Relays, Inverter IC, Relay Driver IC, Voltage Regulator, Diodes, Crystal, Resistors, Lamps., Capacitors, Kiel compiler and Languages: Assembly or Embedded C programming language DTMF based load control system mainly uses a DTMF to control a load system, working and applications are discussed below.
- The 230V AC supply is first stepped down to 12V AC using a step-down transformer.
- This is then converted to DC using the bridge rectifier.
- The AC ripples are filtered out by using a capacitor and given to the input pin of voltage regulator 7805.
- At output pin of this regulator, we get a constant 5V DC which is used for MC and other ICs in this project.
- It is a smaller computer
- Has on-chip RAM, ROM, I/O ports
Features of MC
- 8K Bytes of In-System Programmable (ISP) Flash Memory
- 4.0V to 5.5V Operating Range
- Fully Static Operation: 0 Hz to 33 MHz
- 256 x 8-bit Internal RAM
- 32 Programmable I/O Lines
- Three 16-bit Timer/Counters
- Eight Interrupt Sources
- Full Duplex UART Serial Channel
- This circuit detects the dial tone from a telephone line and decodes the keypad pressed on the remote telephone.
- Two distinct frequency tones make up the DTMF (dual tone multi frequency), and hence the name.
- The dialer and the telephone exchange communicate one way through the DTMF communication.
- The tone generator and the tone decoder consist of a complete communication setup.
- In this project, IC MT8870DE is used to decode the input dial tone to the dialled numbers.
- These digital bits are interfaced to a microcontroller for any application.
- Pulse/dial tone method is used in the modern telephone communication.
- There is a dial tone generator on the caller side and a unique tone consisting of two audible tone frequencies is generated when the user presses a button.
- As an example, 697 Hz & 1209hz will be generated when key ‘1’ is being pressed on the phone.
- a decoder circuit is present on the receiver side, which decodes the tone to a digital code.
- A relay is an electrically operated switch.
- Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts.
- The coil current can be on or off so relays have two switch positions and have double throw (changeover) switch contacts as shown in the diagram.
- Relays allow one circuit to switch a second circuit which can be completely separate from the first.
- For example, a low voltage battery circuit can use a relay to switch a 230V AC mains circuit.
- There is no electrical connection inside the relay between the two circuits; the link is magnetic and mechanical.
- To drive relay through MC ULN2003 relay driver IC is used
Relay Driver ULN2003
- ULN is Relay driver application
- The ULN2003 is a monolithic high voltage and high current Darlington transistor arrays.
- It consists of seven NPN Darlington pairs that feature high-voltage outputs with common-cathode clamp diode for switching inductive loads.
- The collector-current rating of a single Darlington pair is 500mA.
- The Darlington pairs may be paralleled for higher current capability.
- The ULN functions as an inverter.
- If the logic at input 1B is high then the output at its corresponding pin 1C will be low.
- Keil an Arms Company makes C compilers, macro assemblers, real-time kernels, debuggers, simulators, integrated environments, evaluation boards, and emulators for ARM7/ARM9/Cortex-M3, XC16x/C16x/ST10, 251, and 8051 MCU families.
- Compilers are programs used to convert a High-Level Language to object code. Desktop compilers produce an output object code for the underlying microprocessor, but not for other microprocessors. i.e the programs written in one of the HLL like ‘C’ will compile the code to run on the system for a particular processor like x86 (underlying microprocessor in the computer).
- For example compilers for Dos platform is different from the Compilers for Unix platform So if one wants to define a compiler then the compiler is a program that translates source code into object code.
Working of Project
- The main objective of the project is to control the functioning of the industrial/ agricultural load using wireless technology.
- The mobile is connected to the DTMF decoder IC and a call is made to data mobile from another mobile.
- When the network path is formed, any mobile key is pressed.
- If 1 is pressed then this tone is decoded to 4 digit data and given to MC by inverting the data.
- MC compares this data and an output port which is connected to ULN gets logic high and the output of ULN is low which makes the relay ON. Hence, load 1 will be ON.
Advantages and Applications
- Using this technology, the loads can be activated from anyplace
- The applications of DTMF (dual tone multi frequency) mainly include home, industries, agriculture, etc.
- These tones are used at the telephone switch centres for discovery of calls or dialled number and also used by a particular cable network
- This n/w’s uses DTMF tones to specify a local cable operator when a local add is to be put in. In allocation, this is identified as local placing. These tones were also used by global stations for switching ON & OFF remote transmitters
From the above information, finally, we can conclude that by using Dual Tone Multi Frequency technology and microcontroller, the loads can be operated from any place. We hope that you have got a better understanding of this concept or DTMF based 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?