Home Automation using DTMF and 8051

INTRODUCTION

With advancement of technology, things are becoming simpler and easier for us. Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization. Mechanization provides human operators with machinery to assist them with the muscular requirements of work, whereas automation greatly decreases the need for human sensory and mental requirements as well. Automation plays an increasingly important role in the world economy and in daily experience. Automatic systems are being preferred over manual system. Through this project we have tried to show automatic control of a house as a result of which power is saved to some extent.

Sometimes we may forget to switch off the appliances while going outside and then ponder how to switch off these devices while we are out of home. To solve these types of problems, this article explains you how to design a simple circuit, which will on and off the devices remotely by the using of DTMF decoder. Till now we have seen so many circuits to control the devices or appliances from the remote place but the main advantage of this circuit is that it’s simple and we can operate it from anywhere in the world. We are using the microcontroller 8051 in this circuit for controlling different devices.

BASICS OF HOME AUTOMATION

INTRODUCTION

Home/office automation is one of the most exciting developments in technology that has come along in decades. There are hundreds of products available today that allow us Home/office automation. It enables us to control any or all electrical devices in our home or office automatically, either by remote control or even by voice command. Home automation (also called domotics) is the residential extension of “building automation” which refers to the automation of household activity. It may include centralized control of lighting, HVAC (heating, ventilation and air conditioning), appliances, and other systems, to provide improved convenience, comfort, energy efficiency and security. It can provide increased quality of life for differently abled people who might otherwise require help from caregivers or institutional care.

Fig. 1: Block Diagram of 8051 Microcontroller and DTMF based Home Automation System

NEED OF AUTOMATION

Earlier, we looked into the face of future when we talked about automated devices, which could do anything on instigation of a controller, but today it has become a reality.

a) An automated device can replace good amount of human workforce. Moreover, humans are more likely to commit errors and in intensive conditions the probability of error increases, whereas an automated device can work with diligence, versatility and with almost zero error.

o Replacing human operators in tasks that involve hard physical or monotonous work.

o Replacing humans in tasks that are performed in dangerous environments (i.e. fire, space, volcanoes, nuclear facilities, underwater, etc)

o Performing tasks that are beyond human capabilities of size, weight, speed, endurance, etc.

o Economy improvement. Automation may improve the economy of enterprises, society or most of humankind. For example, an enterprise that has invested in automation technology recovers its investment, or a state or country increases its income due to automation like Germany or Japan in the 20th Century.

b) This is why this project looks into construction and implementation of a system involving hardware to control a variety of electrical and electronic systems.

BASICS OF DTMF

INTRODUCTION

DTMF is an acronym for Dual Tone Multi Frequency. When you make a call to the customer care, they ask you to press 1, 2 or any other number and after pressing that number one particular action takes place. All this is because of DTMF. When a button is pressed in your mobile keypad, it generates two frequencies called row and column frequencies. Generally, row frequencies are low and column frequencies are high. These frequencies for DTMF are chosen in such a way that they don’t have harmonic relation with the others, so that they don’t produce same tones. The column frequencies are slightly louder than the row frequencies to compensate for the high-frequency roll off on the voice audio systems.

What is DTMF code..??

When any key like “1”, “2”, “*”, “#” etc is pressed, a particular code is transmitted. This code consists of two frequencies among which one is higher and second is lower. Following table shows the combination of frequency for respected keys.

Fig. 2: Image showing DTMF Frequencies mapped to a typical numeric keypad

According to above table “8” is combination of lower frequency of 852 Hz and higher frequency of1336 Hz and “#” is of lower frequency of 941 Hz and higher frequency of 1447 Hz. So this is all about DTMF code. Now let’s see how DTMF code is generated, transmitted and decoded in mobile phone system. Here I have only discussed about GSM system.

Transmission of DTMF code in GSM network

In GSM networks a lot of channels are available but mainly there are only two channels…

1. Physical Channels

2. Logical Channels

DTMF codes are transmitted in FACCH i.e. fast associated control channel. Complete hierarchy of FACCH is given below.

• GSM Channels

• Logical Channels

• Signaling Channels

• Dedicated Control Channels

• Fast Associated Control Channel

FACCH is a bidirectional channel i.e. uplink and downlink. It is used to transmit and receive emergency controlling signal messages. When any data or message needs to be transmitted through this channel, it replaces the voice signal to digital signaling data for very short amount of time.

Decoding DTMF code

When any DTMF code has been received at mobile phone it is audible through speakers. To decode this DTMF code, speaker output can be used. Output of speaker is connected to IC MT8870 which is a widely used DTMF decoder. It gives 4-bit digital output q1, q2, q3, and q4 according to the received key. Following table shows the equivalent digital output for each key.

Fig. 3: Table showing digital outputs for DTMF Keys

Keypad

Fig. 4: Graph showing waveform for a DTMF frequency

1209 Hz on 697 Hz to make 1 tone

The DTMF teliphone keypad is laid out in a 4×4 matrix of push buttons in which each row represents the low frequency component and each column represents the high frequency component of the DTMF signal. Pressing a key sends a combination of the row and column frequencies. For example, key 1 produces a superimposition of tones of 697 and 1209 (Hz). Initial pushbutton designs employed levers, so that each button activated two contacts. The tones are decoded by the

switching center to determine the keys pressed by the user.

DTMF keypad frequencies (with sound clips)
	1209 Hz	1336 Hz	1477 Hz	1633 Hz
697 Hz	1	2	3	A
770 Hz	4	5	6	B
852 Hz	7	8	9	C
941 Hz	*	0	#	D

Fig. 5: Table showing DTMF Frequencies mapped to key combinations on Keypad

OTHER MULTIPLE FREQUENCY

National telephone systems define other tones that indicate the status of lines, equipment, or the result of calls. Such call progress tones are often also composed of multiple frequencies and are standardized in each country. The Bell System defines them in the Precise tone Plane. However, such signaling systems are not considered to belong to the DTMF system.

BLOCK SCHEMATIC

BLOCK DIAGRAM

Fig. 6: Block Diagram of DTMF Decoder

BLOCK DIAGRAM EXPLANATION

The block diagram includes:

1. MOBILE PHONE

2. DTMF DECODER IC MT8870

3. ATMEL 8051 MICRO CONTROLLER

4. SYSTEM 12V AND 5V POWERSUPPLY

5. RELAY AND DRIVER CIRCUIT

6. DEVICES

1 MOBILE PHONE

This system is designed for controlling the devices; it includes a mobile phone which is connected to the system via head set. To activate the cellular phone part of the system a call is to be made and as the call is answered, in response the user would enter a three/four(as he/she want) digit password to access the system to control devices. As the caller presses a specific password, the device is turned ON or OFF.

2 . DTMF DECODER IC MT8870

The DTMF is generated in cellular phones. Here, by using a cell phone we control the home appliances from anywhere in the world (In Network Area). When we press any key it generates a frequency after mixing two frequencies and then sends it to the receiver end over communication channel. DTMF decoder IC decodes that particular signal frequency to data and forward to the microcontroller to control the particular device.

3 . ATMEL 80c51 MICRO CONTROLLER

This is the most important block of the system. Microcontroller is the decision making logical device which has its own memory, I/O ports, CPU and Clock circuit embedded on a single chip. It receives inputs from DTMF, makes decision according to it and gives input to the relay driver which drives the corresponding relay and turns the devices on and off.

4 SYSTEM 12V AND 5V POWERSUPPLY

Initial stage of every electronic circuit is power supply system which provides required power to drive the whole system. The specification of power supply depends on the power requirement and this requirement is determined by its rating. The main components used in supply system are:

transformer

rectifier

input filter

regulator

output filteroutput indication

5 RELAY AND DRIVER CIRCUIT

A relay is an electrically operated switch that usually makes use of an electromagnet to mechanically operate a switch. However, other operating principles such as solid-state relays may also be used, Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it to another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations. Relay driver circuit drives each relay switch by external 12v supply. In the output of the microcontroller as the voltage is less than about 4.5V it won’t be able to switch the relays. In order to avoid such a condition, we will have to provide an intermediate to the driver circuit.

DTMF DECODER IC MT8870

The MT8870D/MT8870D-1 is a complete DTMF receiver integrating both the bandsplit filter and digital decoder functions. The filter section uses switched capacitor techniques for high and low group filters; the decoder uses digital counting techniques to detect and decode all 16 DTMF tone pairs into a 4-bit code. External component count is minimized by on chip provision of a differential input amplifier, clock oscillator and latched three-state bus interface.

FEATURES

• Complete DTMF Receiver

• Low power consumption

• Internal gain setting amplifier

• Adjustable guard time

• Central office quality

• Power-down mode

• Inhibit mode

• Backward compatible with MT8870C/MT8870C-1

APPLICATIONS

• Receiver system for British Telecom (BT) or CEPT Spec (MT8870D-1)

• Paging systems

• Repeater systems/mobile radio

• Credit card systems

• Remote control

• Personal computers

• Telephone answering machine

PIN DESCRIPTION

Fig. 7: Pin Diagram of MT8870 DTMF Decoder

Fig.(A)

Fig. 8:

Table :(B)

FUNCTIONAL DESCRIPTION

The MT8870D/MT8870D-1 monolithic DTMFreceiver offers small size, low power consumption and high performance. Its architecture consists of a bandsplit filter section, which separates the high and low group tones, followed by a digital counting section which verifies the frequency and duration of the received tones before passing the corresponding code to the output bus.

FILTER SELECTION

Separation of the low-group and high group tones is achieved by applying the DTMF signal to the inputs of two sixth-order switched capacitor bandpass filters, the bandwidths of which correspond to the low and high group frequencies. The filter section also incorporates notches at 350 and 440 Hz for exceptional dial tone rejection (see Figure 3). Each filter output is followed by a single order switched capacitor filter section which smoothes the signals prior to limiting. Limiting is performed by high-gain comparators which are provided with hysteresis to prevent detection of unwanted low-level signals. The outputs of the comparators provide full rail logic swings at the frequencies of the incoming DTMF signals.

DECODER SECTION

Following the filter section is a decoder employing digital counting techniques to determine the frequencies of the incoming tones and to verify that they correspond to standard DTMF frequencies. A complex averaging algorithm protects against tone simulation by extraneous signals such as voice while providing tolerance to small frequency deviations and variations. This averaging algorithm has been developed to ensure an optimum combination ofimmunity to talk-off and tolerate the presence of interfering frequencies (third tones) and noise. When the detector recognizes the presence of two valid tones (this is referred to as the “signal condition” in some industry specifications) the “Early Steering” (ESt) output will go to an active state. Any subsequent loss of signal condition will cause ESt to assume an inactive state (see “Steering Circuit”).

ATMEL AT89c51 MICROCONTRLLER

The 8051 instruction set is optimized for 8-bit control applications. It provides a variety of fast addressing modes for accessing the internal RAM to facilitate byte operations on small data structures. The instruction set provides extensive support for one-bit variables as a separate data type, allowing direct bit manipulation in control and logic systems that require Boolean processing. It is a high performance Flash version of the 80C51 single chip 8-bit microcontrollers. In X2 mode a maximum external clock rate of 20 MHz reaches a 300 ns cycle time. Besides, the AT89C51AC3 provides 64K Bytes of Flash memory including In-System

Programming (ISP) and IAP, 2K Bytes Boot Flash Memory, 2K Bytes EEPROM and 2048 byte ERAM. Primary attention is paid to the reduction of the electro-magnetic emission of AT89C51AC3.

FEATURES

• 80C51 Core Architecture

• 256 Bytes of On-chip RAM

• 2048 Bytes of On-chip ERAM

• 64K Bytes of On-chip Flash Memory

– Data Retention: 10 Years at 85°C

– Read/Write Cycle: 100K

• Boot Code Section with Independent Lock Bits

• 2K Bytes of On-chip Flash for Bootloader

• In-System Programming by On-Chip UART Boot Program and IAP Capability

• 2K Bytes of On-chip EEPROM

Read/Write Cycle: 100K

• Integrated Power Monitor (POR: PFD) To Supervise Internal Power Supply

• 14-sources 4-level Interrupts

• Three 16-bit Timers/Counters

• Full Duplex UART Compatible 80C51

• High-speed Architecture

– In Standard Mode:

40 MHz (Vcc 3V to 5.5V, both Internal and external code execution)

60 MHz (Vcc 4.5V to 5.5V and Internal Code execution only)

– In X2 mode (6 Clocks/machine cycle)

20 MHz (Vcc 3V to 5.5V, both Internal and external code execution)

30 MHz (Vcc 4.5V to 5.5V and Internal Code execution only)

• Five Ports: 32 + 4 Digital I/O Lines

• Five-channel 16-bit PCA with

– PWM (8-bit)

– High-speed Output

– Timer and Edge Capture

• Double Data Pointer

• 21-bit WatchDog Timer (7 Programmable Bits)

• A 10-bit Resolution Analog to Digital Converter (ADC) with 8 Multiplexed Inputs

• SPI Interface (PLCC52 and VPFP64 packages only)

• On-chip Emulation Logic (Enhanced Hook System)

• Power Saving Modes

– Idle Mode

– Power-down Mode

• Power Supply: 3 volts to 5.5 volts

• Temperature Range: Industrial (-40° to +85°C)

• Packages: VQFP44, PLCC44, VQFP64, PLCC52

BLOCK DIAGRAM

Fig. 9: Internal Block Diagram of 8051 Microcontroller

PIN CONFIGURATION

Fig. 10: Pin Diagram of AT89C51 8051 Microcontroller

Fig (A) Pin configuration

Fig. 11: Table showing pin configuration of AT89C51 8051 Microcontroller

ELECTRICAL CHARACTERISTICS

Absolute Maximum Ratings

Ambiant Temperature Under Bias:

I = industrial ………………………………………………. -40°C to 85°C

Storage Temperature ……………………………… -65°C to + 150°C

Voltage on VCC from VSS ………………………………..-0.5V to + 6V

Voltage on Any Pin from VSS………………… -0.5V to VCC + 0.2V

Power Dissipation …………………………………………………….. 1 W

DC Parameters for Standard Voltage

TA = -40°C to +85°C; VSS = 0V;

VCC =2.7V to 5.5V and F = 0 to 40 MHz (both internal and external code execution)

VCC =4.5V to 5.5V and F = 0 to 60 MHz (internal code execution only)

HARDWARE IMPLEMENTATION

CIRCUIT DIAGRAMS

Circuit Diagram of DTMF Decoder

Fig. 12: Circuit Diagram of DTMF Decoder

(Check the circuit diagram tab for complete circuit for Home Automation using DTMF and 8051)

Fig. 13: Circuit Diagram of relay driver used for controlling home appliances

Fig. 14: Circuit Diagram of Relay Driver used for controlling home appliances

CIRCUIT DESIGN

POWER SUPPLY

Here the main power supply source is 12v ac to dc rectifier circuit. We have used full wave bridge rectifier and regulated IC 7812. A regulated power supply is an embedded circuit which converts unregulated AC into a constant DC volt with the help of a rectifier.. Its function is to supply a stable voltage to a circuit or device that must be operated within certain power supply limits. The output from the regulated power supply may be alternating or unidirectional but it’s always nearly DC. The figure given below shows the power supply unit.

Fig. 15: Circuit Diagram of Rectifier and 7812 12V Power Regulator

1 TRANSFORMER : A transformer is an electrical device that transfers energy between two or more circuits through electromagnetic induction. A varying current in the transformer’s primary winding creates a varying magnetic flux in the core and a varying magnetic field impinging on the secondary winding. This varying magnetic field at the secondary induces a varying electromotive force (EMF) or voltage in the secondary winding. Making use of Faraday’s Law in conjunction with high magnetic permeability core properties, transformers can thus be designed to efficiently change AC voltages from one voltage level to another within power networks.

Fig. 16: Typical Image of 12V Step-Down Transformer

2 REGULATED POWER SUPPLY: Here our main power supply source is 12V AC to DC rectifier circuit. We have used full wave bridge rectifier, regulated IC 7812 and IC 7805A regulated power supply. IC 7805A is an embedded circuit that converts unregulated AC in to a constant Dc volt with the help of a rectifier.. Its function is to supply a stable voltage to a circuit or device that must be operated within certain power supply limits. The output from the regulated power supply may be alternating or unidirectional, but it’s always nearly DC. Below mentioned fig shows the power supply unit.

Fig. 17: Pin Diagram of 7812 Voltage Regulator IC

Here we used 12v and 5v regulated supply because microcontroller usually works at +5V. So to get that voltage, we need a voltage regulator as 5v for which we have used an IC 7805. The current capacity of this regulator is 1A. If you need more current either use a number of them in parallel or switch to another voltage regulator whose current capacity is more.

Fig. 18: Pin Diagram of 7805 Voltage Regulator IC

RELAY AND DRIVER

A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it to another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations.

Fig. 19: Typical Image of Relays

One of the serious problems in relay operated circuits is the relay clicking or chattering during the on/off of the relay driver transistor. This problem is severe if the input circuit is a light/temperature sensor. By using a simple tip, this problem can be avoided. Below is the circuit of a relay driver using the NPN transistor BC 548. The relay is connected between the positive rail and the collector of the transistor. When the input signal passes through the I K resistor to the base of the transistor, it conducts and pulls the relay. By adding a 470 uF electrolytic capacitor at the base of the relay driver transistor, a short lag can be induced so that the transistor switches on only if the input signal is persisting. Again, even if the input signal ceases, the transistor remains conducting till the capacitor discharges completely. This avoids relay clicking and offers clean switching of the relay. Relay Driver Circuit transistor relay driver circuit schematic*(meaning not clear) Another 470uF capacitor is added parallel to the relay coil which maintains steady current so that relay clicking can be avoided if the power supply varies.

VARIOUS DEVICES USED

RESISTORS

A resistor is a two-terminal electrical or electronic component that opposes an electric current by producing a voltage drop between its terminals in accordance with Ohm’s law. It states that the electrical resistance is equal to the voltage dropped across the resistor divided by the current through the resistor while the temperature remains the same. Resistors are used as a part of electrical networks and electronic circuits.

Fig. 20: Image of Resistors used in Rectifier Circuit

CAPACITORS

A capacitor is an electrical or electronic device that can store energy in the electric field between a pair of conductors. The process of storing energy in the capacitor is known as “charging” and involves electric charges of equal magnitude but opposite polarity, building up on each plate. Capacitors are often used in electric and electronic circuits as energy-storage devices. They can also be used to differentiate between high frequency and low frequency signals. This property makes them useful in electronic filters.

Fig. 21: Image of Capacitors used in Rectifier Circuit

CRYSTAL OSCILLATOR

A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time, to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitter and receivers. The most common type of piezoelectric resonator used is the quartz crystal, so oscillator circuits incorporating them are known as crystal oscillators. Other piezoelectric materials including polycrystalline ceramics are used in similar circuits.

Quartz crystals are manufactured for frequencies from a few tens of kilohertz to hundreds of megahertz. More than two billion crystals are manufactured annually. Most of them are used as consumer devices such as, wristwatches, clocks, radios computers and cell phones. Quartz crystals are also found inside test and measurement equipment, such as counters, signal generators and oscilloscopes.

Fig. 22: Typical Image of Crystal Oscillator

CONECTING MOBILE PHONE WITH MT8870

Our main aim is to connect mobile phone’s speaker output to MT8870 and for achieving this we will use aux cable which has 3.5mm male audio jack at both its ends as shown in below image. 3.5mm audio jack is a TRS connector which is Tip Ring Sleeve (ground) as shown in below image. Now we will use 3.5mm female audio jack to get mobile phone’s speaker output and connect it with MT8870. Go through the following images to get clear understanding.

Fig. 23: Pin Description of 3.5 MM Audio Jack used with DTMF Decoder

SOFTWARE IMPLIMENTATION

COMPILER & IDE

Fig. 24: Block Represeentation of C Program Compilation

We are writing the program in embedded C .The compiler that we used is KIEL and the IDE is AVR Studio

PROGRAM ALGORITHM

1) Start.

2) Initialize the input port & output port.

3) Read data from port C.

4) Check the input conditions, if the all conditions where cheked.

5) Corresponding output will print.

FLOW CHART

Fig. 25: Flow Diagram of C Code used for detection of DTMF Frequencies

PCB DESIGN AND FABRICATION

Printed circuit board fabrication is one of the essential and the prominent step in the formation of one electronic device .In this section we are explaining about the formation of PCB. The design of a PCB can be considered as the last step in electronic circuit designing .In the electronic circuit performances and reliability depends on the productivity of the PCB. Assembling and service ability also on the design .A proper ensure that various components are interconnected as there the circuit diagram. Once they have been placed on the PCB in their proper position and subsequently soldered. PCB design and fabrication techniques have undergone so much of development that it has become a subject in itself. Double sided PCBs with plated through holes (PTH) flexible PCBs etc. are only some of the developments .The single sided PCBs are usually using the print and etch method and double –sided plates through hole boards are made by print ,plate and etch method. The production of multilayer boards used both the techniques.

PREPARING LAY-OUT

The track layout of the electronic circuit must be drawn on a white paper .The layout should be made in such way that paths are in easy rotes. This enables the PCB to be more compact and economical. For making the PCB layout we are using the software ORCAD.

First open ORCAD, from there select the option ‘capture’. To draw a new design follow steps, file → new → project path→ file name. To get the circuit components select the second icon from top right and to get the wire for interconnection take 3rd icon from the top right.

After completing the circuit drawing next is the error correction. For error correction take schematic → page1.To give numbers to the components follow the steps, Annotate→ Reset path reference Annotate→ increment reference→ OK.

The next step is the design rule checking. For DRC perform following steps. DRC→ Create net list→ layout→ Run ECD to

layout→ save.

To make the layout the procedure is ORCAD→ layout+ → file → new → load →

Template files→ Program file→ ORCAD→ layout+ → data → default

The next step describes rooting, for that: system settings →display units → change unit

Auto root → global spacing→ select bottom→ Right click → properties →

Spacing (set all values to one) for the selection of the layer: view→ data base spread sheet→ layers→ bottom→Used. Select

all others to unused.

The next is the selection of width, for which the steps are: view→ database spread sheet

Select all→ right click → properties → set as 1mm→ auto → auto root → board.

TRANSFERRING THE LAY OUT TO COPPER

The layout made on the white paper should be redrawn on the copper clad using paint or nail polish.

Fig. 26: PCB Layout of DTMF based Home Automation Circuit

CONCLUSION

This project was completed within constraints of time, availability of resources and the scopes of the subject covered in the curriculum till the present semester. Here we have made an attempt to reduce human effort by Automation. Our automation could perform various tasks like industrial applications. We hope our project will be beneficial to various fields.