ASK based Device Control

  

1.    INTRODUCTION

               The project titled “ASK based Device Control” is designed to help the user to control the devices at his home remotely. The system introduced here is configured to control 4 different devices by means of a portable hand set from distance up to 150 meters. Various electrical equipments in home or office can be controlled using this system

Through this system we can switch ON three devices by pressing 3 different push-buttons. But pressing the fourth button will switch off the whole devices simultaneously. This system makes use of an RF transmitter and receiver module to transmit and receive codes to control different appliances remotely from distant places.

The system is designed such that the user is relieve of walking un necessary to control his appliances Though this system is designed for home automation, It can be used for many other applications such as

1.   Dish antenna positioning

2.   Camera control

3.   Search light control

4.   Robotic arm control

      5.   Motor speed control etc

           

2.                 BLOCK diagram

The block diagram of ASK based device control system is shown in fig above. This system essentially consist two units as control unit and switching unit

3.    BLOCK explanation

3.1 Control unit

This unit consist an encoder and an RF transmitter.The function of the encoder section in this system is to set a code format for switching of each device at home .Each bit of code can be set to one of the two logic states(0 or 1 In this section H-12E encoder IC is used. It is capable of encoding 12 bit of information with N address bit and 12-N code bit. The required bit format to be transmitted can be formed by setting the position of switches assigned to each device in either ON or OFF position, the format bits from encoder are serially fed to the RF transmitter module.

The bit format from the encoder section are transmitted together with the Address bits via an RF transmission medium.. The transmitter module used here is a 433MHZ ASK transmitter which does not requires any external components and no tuning. These transmitted signals are receive by the RF receiver located at switching unit

The control unit is powered by a 9V portable cell

3.2 Switching unit

            The various sections in the switching unit of this system are as follows

1. RF receiver module

2. Decoder

3. Relay driver

4. Power supply

           

           The  RF receiver module is a  433MHZ ASK receiver tuned to receive 433MHZ signal from the transmitter .On receiving the signal from the transmitter it feeds the out put code to the decoder section

            The decoder section decodes the exact format of code bits from the received signal and provides output as 4bits the de coder H-12D Ic is used in this section. This IC is capable of decoding information of 12 bits. The output bits from the decoder is fed to the relay driver

             There are 4 electromagnetic relays in this circuit. They are used to control 4 devices. The function of the relay driver stage is to provide sufficient current to activate these relays. In this circuit four NPN transistors are arranged to drive these relays.

            This system requires A supply of regulated +5V for the operation RF receiver and decoder circuit. It also requires a 9v supply for the operation relay driver section. The power supply section consists of step-down transformer; a bridge rectifier and a 5v regulator with filter circuit

4. CIRCUIT DIAGRAM

Fig (a)

 Fig (b)

5. CIRCUIT Explanation

The circuit diagram of home automation system is given as two parts in fig (a) and (b). Fig (a) shows the circuit for control unit of the system and fig (b) shows the switching unit. Description on different sections of the circuit are given below

5.1 Control unit

           The control unit of the system consists of three sections as control switches. Encoder and RF transmitter.

5.1.1 Control switches

            Control switches are simple ON/OFF switches. These switches are connected to 4 data input pins of he encoder IC with other end grounded so as to keep the status of these pins high in its ON position and low in its OFF position. In this system four such switches are used so as   to control four different devices.

5.1.2 Encoder

   In this circuit HT-12E IC is used as encoder. The Holtek HT-12E IC encodes 12-bits of information and serially transmits this data on receipt of a Transmit Enable, or a LOW signal on pin-14 /TE.  Pin-17 the D_OUT pin of the HT-12E serially transmits whatever data is available on pins 10, 11,12 and 13, or D0,D1,D2 and D3 along with address bits set at pin-1 through pin 8.. Using the address pins of the HT-12E, we can select different addresses for up to 256 receivers. In this system address is set as 11111111 by keeping all address pins at high status.(connected to Vcc) Data is transmitted at a frequency selected by the external oscillator resistor. (See the encoder/decoder datasheets for details). In this circuit the TE pin is grounded permanently and the 4 control switches are connected to the pins D0-D3.  T

he bit format required to switch ON/OFF each device can be set by keeping the position of the concerned switch in ON/OFF position. This bit pattern is fed serially to the Din pin of the RF transmitter module.

5.1.3 RF transmitter

The RF transmitter used in this system is TWS-434 ASK module. It is excellent for applications requiring short-range RF remote controls. .  The transmitter module is only 1/3 the size of a standard postage stamp, and can easily be placed inside a small plastic enclosure.

The transmitter output is up to 8mW at 433.92MHz with a range of approximately 400 foot (open area) outdoors.  In doors, the range is approximately 200 foot, and will go through most walls.

The TWS-434 transmitter accepts both linear and digital inputs can operate from 1.5 to 12 Volts-DC, and makes building a miniature hand-held RF transmitter very easy. The bit pattern received from the encoder IC will be transmitter from this module in amplitude shift key modulated form

5.2 Switching section

The complete circuit diagram switching section of the system is shown in fig (b). This part of the system consist different section. As RF receiver, Decoder, Relay driver, Relays and Power supply. Description on various sections is as explained below

5.2.1 RF receiver

The RF receiver module used in this circuit is RWS-434 module, which is designed to receive the signal transmitted from TWS-434 transmitter module without any tuning circuitry .The RWS-434RF receiver module receives the incoming RF signals from the TWS-434 transmitter. The TWS-434 outputs this incoming data stream to the DIN pin of the decoder IC.

5.2.2 Decoder

The decoder IC used in this circuit is HT-12D. It receives the 12-bit word and interprets the first 8-bits as address and the last 4-bits as data. The address selected on the HT-12E circuit must match the address selected on the HT-12D (pin1 through 8), or the information will be ignored by the receiving circuit. When the received addresses from the encoder matches the decoders, the Valid Transmission pin-17 of the HT-12D will go HIGH to indicate that a valid transmission has been received and the 4-bits of data are latched to the data output pins, 10-13. The HT-12D data output pins will LATCH and remain in this state until another valid transmission is received. In this circuit data output from pins (D0-D3) is connected to the input of 4 Darlington amplifiers

5.2.3 Relay drivers

            The output current from the output pins of the decoder IC is not sufficient to drive an electromagnetic relay used to control a device. Hence a driver stage is to be used between decoder and relay circuits. In this system a single NPN transistor BC548 is used to drive each relay. The relay coil is connected in series

to the collector of the circuit. The transistor Q1 saturates as soon as its base voltage exceeds the 0.7V. Thus the Q1 acts as a closed switch and supplies sufficient current to energies the relay. The relay will be switched OFF as soon as the input voltage falls below the 0.7V

                  Relays can generate a very high voltage across the coil when switched off. This can damage other components in the circuit. To prevent this diode is connected across the coil. This diode will act as the surge protection device. This diode will goes to the forward biased condition whenever a surge voltage appears across it. Thus the surge voltage gets a shorts circuit through the diode and the rest of the circuit will not be affected by the surge.

                

5.2.4 Relays

           Since this system is meant to control four different devices. Four electromagnetic relays are used in the switching section. The electromagnetic relay consists of a multi-turn coil, wound on an iron core, to form an electromagnet.  When the coil is energized, by passing current through it, the core becomes temporarily magnetized. The magnetized core attracts the iron armature. The armature is pivoted which causes it to operate one or more sets of contacts. When the coil is de-energized the armature and contacts are released.

    The coil can be energized from a low power source such as a transistor while the contacts can switch high powers such as the mains supply.       

 5.2.5 Power supply

             This system requires two power sources of regulated 5V and                          unregulated 12V the regulated 5V used for the operation of RF receiver and decoder circuit where as 12V is required for the operation of relay drivers

The 5V supply section consists of a step-down transformer (230V/12V500MA), bridge rectifier diodes D1 through D4 (each IN4007), filter capacitor (1000MFD,25v) and regulator IC7805.

This circuit provides a regulated voltage of 5V.  The un regulated 12V is tapped from the input of the regulator IC

6. COMPONENT LIST

COMPONENTS	SPECIFICATION	QTY
ASK TRANSMITTER MODULE	PCR 2A ,433 MHz	1
ASK RECEIVER MODULE	PS 1000A,433MHz	1
ENCODER	IC (HT 12E)	1
DECODER	IC(HT 12 D)	1
RESISTER	470 OHM 1 K 1.8 K 100K 1 M 10 K	1 4 4 1 1 4
SWITCHES	TOGGLE TYPE	4
RELAY	SPDT	4
TRANSISTER	BC 549	4
LED		5
VOLTAGE REGULATOR	LM 7800 (TO 220)	1

7. HARDWARE DISCRIPTION

7.1 ASK TRANSMITTER MODULE

             The ST-TX01-ASK in an ASK Hybrid transmitted module. ST-TX01-ASK is designed by the saw resonator with an affective low cost , small size and simple to use for designing. The freq. Range is 315/433.92 MHz. the supply voltage is 3-12 volt. It’s widely used in wireless security system, car alarm system, remote controls, sensor reporting and automation systems.

7.2 ASK RECEIVER MODULE.

       

The ST-RXO2-ASK is an ASK Hybrid receiver module. The frequency range is 315/433.92 MHz. the main features low power consumption, easy for application. The operating temp. Ranges from -20 to +70^o C. the operating voltage is +5V. It’s widely used in wireless security system, car alarm system, remote controls, sensor reporting automation system and remote keyless entry etc.

7.3 ENCODER

 

            The 2¹² encoders are a receiver of CMOS LSIS for remote ctrl system applications. They are capable of encoding information which consist of N address bits and 12-N data bits. Each address/data inputs can be set to one of the two logic state. The programmed address/data are transmitted together with the headers bit via. RF or an IR transmission medium upon receipt of trigger signal. The capability to select a trigger on the HT-12E or a data trigger on the HT 12A further enhance the application. Flexibility of the 2¹² receiver of encoders. The HT12A additionally provides a 38 KHz career for IR systems.

They are mainly used in Burglar alarm systems, smoke and fire alarm systems, garage door ctrls, car door ctrls, Codeless telephones etc

7.4 DECODERS

 

The 2¹² decoders are a receiver of CMOS LSIS for applications.  Remote control system. They are paired with Holtek’s 2¹² receivers of encoders. For proper operation of pair of encoders or decoders with the same number of addresses and data format should be chosen.

The decoders receive serial addresses and data from a programmed 2¹² receiver of encoders that are transmitted by a carrier having an RF or an IR transmission medium. They compare the serial input data these times continuously with their local address. If no error or unmatched codes are found, the input data are codes decoder and then transferred to the pins the VT pins also goes high to indicate a valid transmission.

   

The 2¹² receiver of decoders are capable of decoding information that consists of N Bits of address and 12 N bits of data of these receiver the HT 12D is arranged to provide 8 address bits and 4 data bits and HT 12F is used to decode 12 bits of address information.

7.5 VOLTAGE REGULATOR

TO 220

            The LM 78XX receivers of 3 terminal positive regulators are available in the TO 220 /D-PAK package and with several fixed output voltages making them useful in a wide range of applications. Each type employs internal current limiting, thermal shut down and safe operating area protection making it essentially indestinctible.

     

 If adequate heat sinking is provided, they can deliver over IA output current . Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltages and components. The main features are short circuit protection and thermal overload protection.

 

8. PCB LAYOUT

 

9. PCB DESIGN

The various steps involves in PCB fabrication are listed below;

·         Prepare the components layout into PCB layout.

·         Convert the copper-clad sheet into desired size.

·         Clean the copper –clad sheet.

·         Trace the PCB layout on the copper side.

·         Prepare etching solution by mixing ferric chloride with water.

·         Etch the PCB for the desired time.

·         Clean the PCB and drill the pads.

·         Solder the components according to the circuit diagram.

                                                                              

 PCB FABRICATION

The printed circuit board (PCB) provides the electrical interconnections between various components and as well as provides mechanical support to the components. The components are soldered to the PCB. The quality of soldering directly affects the reliability of the circuit.

The printed circuit board consist the following steps.

1.      Lay out preparation

2.      Artwork Preparation

3.      Film Master Production

4.      Pattern transfer

5.      Etching

6.      Drilling

9.1 LAYOUT PREPARATION     

The layout is commonly prepared in the scale of 2:1. It offered a reasonable compromise below accuracy gained and handling convenience 2:1 artwork as the actual PCB area. Grid systems are commonly used for preparing the layout. The use of the grid sheet gives more convenience in placement of components and conductors. The grid system based on 0.1 is found to be too coursing, a grid equidistant of 0.025 or even 0.1 mm is recommended.    

 Procedure        

Each and every PCB layout is viewed from component side.

1.      The designing of the layout is started with an absolutely clear component list and circuit diagram is available.

2.      The larger component are placed first and the space in between is filled with area

3.       In the designing of the PCB layout, It is very importance to divide the circuit in to functional sub units

4.      The components are placed in the grid sheet tanning the standard length and width.

5.      The punched lay out is circled to taking the standard size of the land pads

6.       These pads are entering connected as the circuit diagram.

7.      The mirror image of these gives the solder side of the PCB.

9.2 PATTERN TRANSFER

          After the film is processed the film master are obtained. The transfer of the conductor which on film master on to the copper clad base material is done by two methods mainly photo printing and screen printing. Photo printing is extremely accurate process which is also applied to the fabrication of semi-conductors.

Screen printing is comparatively cheap and simple method for transfer although less precise then photo printing.

9.3 SCREEN PRINTING

In screen printing, the process is very simply. A screen fabric with uniform meshes and opening is stretched and fixed on a solid frame of metal or wood. The circuit pattern is photographically transferred on to screen, leaving the meshes in the rest of area as closed. In the actual printing step ink is forced by moving queue through the open master on to the surface of the material to be printed. The light sensitive material is coated on to the screen and using film master the pattern is transferred to the screen. The using ink and the pattern is transferred to the copper clad sheet.

Two methods are used for screen printing into screen

1.     Direct method

2.     Indirect method.

            In direct method than photographically sensitive emulsions are used for transferring patterns. The Wet material is uniformly coated to the screen and then exposed. In indirect method, the photographically sensitive film is transferred to screen. The film is exposed and ten it sticker in to the screen. The pattern is then transferred to the screen using the links and squeegee.

9.4 ETCHING

The removal of unwanted copper from the copper clad sheet is known as etching. For this 4 types of tanks are used.

1.     Ferric chloride

2.     Cupric chloride

3.     Chromic acid

4.     Alkaline ammonia

            Among these ferric chloride is cheap and popular etchant is ferric chloride and also suited for home and industrial applications.

9.5 DRILLING

          Drilling of component mounting holes in to PCBs is by the most important mechanical machining operation PCB production process. The importance of the whole drilling on PCB has further group with electronic component miniaturization and its need for smaller whole Diameters and higher package density where whole purchasing is practically routed out. Four types of drilling are commonly used

1.      Drilling by direct sight.

2.      Drilling by optical slight.

3.      Jig drilling.

4.      NC drilling.

9.6 COMPONENT MOUNTING

Components are basically mounted on one side of the board. On polarized two lead components are mounted to give the marking or orientation throughout the board. The component orientation can be both Horizontal as well as vertical but uniformly, directions are placed.

10. SOLDERING

            Soldering is the process of joining two or more similar or dissimilar metals by melting another metal having lower melting point.

.

10 .1 SOLDERING FLUXES

            In order to make accept the solder readily; the components terminals should be free from oxides and other obstructing films. Soldering flux cleans the oxides from the surface of the metal Zinc Chloride, ammonium Chloride and Rosin are the commonly used fluxes.

10.2 SOLDER 

            Solder is used for joining two or metals at temperature below their melting point. The popularly used solders are alloy of Tin (60%) and Lead (40%) that metals at 375f and solidifies when it cools.

10.3 SOLDERING IRON

            It is used to melt the solder and apply at the joints in the circuit.

11. ADVANTAGES

Ø             The circuit is simple

Ø             Low cost circuit

Ø             It’s easy to use

Ø             It’s more suitable for  physically unable persons

Ø             Can operate anywhere within its range

12. DISADVANTAGES

Ø            Devices can control only up to 150 meters

Ø           The number of devices it can handle is limited

13. APPLICATIONS

1. The system can be used for home automation
2. It can be used in Auditoriums
3. Dish antenna positioning
4.  Robotic arm control
5.  Motor speed control
6. Camera control

14. CONCLUTION

             Our projects entitled ASK Based Device Control is concluded with the desired output. The   desired output was   obtained by receiving the signal from the remote and controlling the output device.

      15. FUTURE scope

Ø  We can extend the range from 150 mtrs by using software techniques

Ø  We can extend the number of devices to be controlled

Internal Block diagram of LMXX

Negative output voltage ckt

Pin description of :

ASK Receiver

ASK Transmitter