Wireless Device control by pc RS 232 Interface
This kit use the RF transmitter receiver units as (as supplied separately) to control 8 relays. The transmitter unit has connected with pc rs 232 port and sending 8 data byte by pc. In the receiver section, receives valid data code once turns on one relay. A second time it’s off .RED LED’s indicate the state off the relay. So it can be viewed from a distance. 12v relay contacts 220V/3A.
With the rapid progress in computer technology many people now have a surplus 8088 or 286 computer just gathering dust somewhere .any thoughts that it could be given away magnamously to ' the kid ' are quickly when those some kids immediately recognize the offer for what it is , turn up their noses and bring out their on CD ROM games and Pentium 2 , 450MHz computer connected to the internet .thus these computers are free to be used as dedicated controllers for variety off uses ; turning on / off light or other devices around the home , office , laboratory or factory come to mind .all that is needed is the interface to connect it to real world . This kid provides in directly to the serial (rs232 port) of your computer .the kid is constructed on signal -sided printed circuit.
* Working voltage - 12v ac/ dc
* Operating c/n - 5ooma aprox
* Contact rating - 230 v ac/500w
* Pc serial port -rs232 interface
* Software for win 95 ,98.2000, xp
* Using 434/315mhz RF freq
* Using amplitude shift keying modulation
* Long range(>300 meters)
* Eight 12v relay
* For up to 8 device to be connected
* On board relay LED indicator
* On board power LED INDICATO
o HOME AUTOMATION
o ROAD LIGHT CONTROLLING
o IN HOSPITAL
o INDUSTRIAL CONTROL SYSTEM
o RAILWAY SIGNAL CONTROL SYSTEM
WHAT IS A MODULATION?
It is the process where the radio freq or light wave’s amplitude freq or phase is changed in order transmits intelligence the characteristics of the carrier wave are dust instantaneously varied by another “modulating” waveform.
There are many ways to modulate the signal
o AMPLITUDE SHIFT KEYING
o FREQUENCY SHIFT KEYING
o AMPLITUDE MODULATION
o FREQUENCY MODULATION
o phase MODULATION
o pulse MODULATION
Amplitude shift keying (ask) is the form of modulation that represents digital data as variations in the amplitude of carrier wave.
The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal), keeping frequency and constant. The level of amplitude can be used to represent binary logic 0s and 1s. We can think of a carrier signal as an ON or OFF switch. In the modulated signal, logic 0 is represented by the absence of a carrier, thus giving OFF/ ON keying operation and hence the name given.
Like AM, ASK is also linear and sensitive to atmospheric noise distortions propagation conditions on different routes in PSTN, etc. it requires excessive bandwidth and is therefore a waste of power. Both ask modulation and demodulation process are relatively inexpensive the ask technique is also commonly used to transmit digital data over RF transmitter data input low level pulse represent binary 0 while high level pulse represents binary 1.
HOW IT WORKS TRANMITTER SECTION
On the computer there is an application program. In that there are 8 buttons switch on or off different devices. When click anyone button the specific code is generated and this code will pass to the circuit using serial port. In the transmitter U1micro controller to use for convert the serial data into the BCD code is passed to RF encoder ic i.e. HT12E .it sends the data wirelessly with the help of Radio frequency transmitter.
RS -232 is simple, universal, well understood and supported but it has some serious shortcomings as a data interface. The standards to 256 kbps or less and line lengths of 15m (50ft) or less but today we see high speed ports on our home pc running very high speeds and with high quality cable maximum distance has increased greatly. The rule of thumb for the length a data cable depends on speed of the data, quality of the cable.
Electronic data communication between elements will generally fall into two broad, categories: single-ended and differential RS232 (single ended) was introduced in 1962, and despite rumors for its early demise, has remained widely through the industry. Independent channels are established for two way (full duplex) communications.
The RS232 signals are represented by voltage levels with respect to a system common (power/logic ground) the “idle” state (mark) has the signal level negative with respect to common , and the “active state (space) has the signal level positive with respect to common .rs 232has numerous handshaking lines (primarily used with modems ) , and also specifies a communication protocol.
The RS 232 interface presupposes a common ground between the DTE and DTC. This is a reasonable assumption when a short cable connects the DTE to the DCE, but with longer lines and connections between devices that may be on different electrical busses with different grounds this may not be true.
RS232 data is bipolar …. +3 to +2v indicates that” on or 0 state (space) condition” while a -3 to -12v indicates an “off “1 state (mark) condition……..Modern computer equipment ignores the negative level and accept a 0 v as the “off” state. Infect the “on” state may be achieve with lesser positive potential this means circuit powered by 5vdc are capable of driving RS232circuits directly , however the overall range that the RS232 signal may be transmitted/received may be dramatically reduced.
The output signal level usually swing between +12v and -12v. The “dead area” between +3v and -3v is designed to absorb line noise. In the various RS232 like definitions this dead area may vary. For instance, the definition for v.10 has a dead area from +0.3v to –o.3v. Many receivers designed for RS232 are sensitive to differentials of 1v or less.
RS232 is a voltage loop interface for two way (full duplex) communication represented by voltage levels with respect to system ground (common) . A common ground between the pc and the associated device is necessary. Maximum serial cable length is defined: 75 feet at 9,600 bps, but today cables up to 1,000 feet are used successfully. The interface is single ended (connecting only two devices with each other), the data rate is less than 20 kbps.
* MICRO CONTROLLER (TX)
The full circuit of the projects is shown in schematic diagram the brain of the switcher is the pre programmed micro controller use as serial to parallel converter. It’s used to encode the pc data, and fed to the RF encoder chip HT12E.
The function of the micro controller is to receive commands (eight data) (through portr3) from the PC via serial port (RS232). Send the BCD code to the RF Encoder as per the commands.
o The 18 Pin micro controller PIC 16F628 Port
RBO-RB3 is used for sending BCD data to the RF encoder chip
o Port A (RA2,RA3,&RA4)is pulled up via 10K resistor & used for manual key control.
RA3 receives the commands from PC serial Port, via the current limit resistor.
SPECIAL MICRO CONTROLLER FEATURES
Power on Reset(POR)
o Its own on chip RC oscillator for reliable operation
o Internal EEPROM
o Multiplexed MCLR-pin
o Programmable weak pull-ups on PCRTB
o Programmable code protection
o Low voltage programming
o Power saving SLEEP mode
o Selectable oscillator options
o FLASH configuration bts for oscillator options- ER (External Resistor) oscillator
o Reduced part count
o Dual speed INTRC
o Lower current consumption
o 16 I/O pins with individual direction control
o High current sink/source for direct LED drive
PIN OUT DIAGRAM OF IC 16F62X
RF Encoder (HT12E)
The 12bit encoders are a series of CMOS remote control systems applications. They are capable of encoding information that consists of eight address bits and four data bits. Each address / data input can be set to one of the two logic states. The programmed address / data are transmitted together with the header bits via and RF transmission medium.
This is low coast A.S.K SAW transmitter module. It makes RF remote techniques easily. Just input that data code and output with a high stability RF signal.
* SAW chip on board technology
* Low power consumption
* Wide range of operation voltage: 1.5 15 volts
* Easy for application
* RF output – 10 + 16dBm at 3V DC operation voltage.
* Available frequency at follows: 315/433.92 MHz
1] RF ASK Receiver Module
This an ASK Hybrid receiver module. It an effective low cost solution to receiving data
at 315 / 433 MHz.
2] RF Data Decoder (HT12D)
The decoders receive serial addresses and data from a programmed 12 bit encoders that are transmitted by a carrier using an RF transmission medium. They compare the serial input data three times contiounsly with their local addresses. If no error or unmatched
3] Micro Controller Interface (BCD Decoder)
The full circuit of the projects is shown in schematic diagram the brain of the receiver is the Pre programmed micro controller use as BCD Decoder.
The function of the micro controller is to receive commands (four bit BCD data) (through port RA0 to RA3) from the RF decoder IC HT 12D and control eight relays via relay driver IC ULN2803. RA0 to RA3 as BCD input, it connect with the RF encoder with 10K pull – ups resistor. A 4 MHz Resonator Connect with OSC1 and OSC2 PIN (15 and 16). Its generates the clock pulse, which fixes the operation speed. Putting the capacitors the crystal (or ceramic) oscillator outside does the oscillation operation. When having the oscillation with the high stability, it uses the crystal. Generally, the circuit becomes simple when using the resonator, which incorporated the ceramic and the capacitor into the one .
RELAY DRIVER (ULN2803)
A single pole dabble throw (SPDT) relay is connected to pin 6 to 13 (RB0 to RB7) of the micro controller through a driver IC ULN2803. The relay requires 12 volts at a current of around 50 ma, which can not provided by micro controller. So the driver IC or transistor is added. The relay is used to operate the external electrical device. Normally the relay remains off. As soon as pin of the micro controller goes high, the relay operates. The connected LED will glow to show that this replay is on. When the relay is switch on it is cut off and signals are directly provided to the connected device through AC power supply.
Two supplies are required for circuit. A DC or AC 12V mains adaptor is connected to bridge rectifier (D1 – 4) via CN5 connecter. U1, U2 AND U3 are supplied with regulated 5V from a 7805(U4) fixed voltage Regulator. The unregulated voltage of approximately 12V is required for relay driving circuit (U3) and eight – 12V SPDT relay.
R1, 2, 4, 6 -1k [4nos]
C1,3 -100n [2 nos]
Y1 -4MHZ OR 8 MHZ RESONATORS
D1 -1N4007 DIODE
L1 -5MM OR 3MM RED LED
L2 -5MM OR 3MM GREEN LED TRANSMITTER
U1 -434/315MHZ ASK RF
U2 -PIC 16F628 PRE PROGRAMMED MICRO
U3 -HT 12ERF ENCODER
U4 -LM7805 5V VOLTAGE REGULATOR
CN1 -9PIN D CONNECTOR
2NOS -18 PIN IC SOCKET
1NOS -RS232 DATA CABEL
R1-5 -10K (5NOS)
C1,3,4 -100N [3NOS]
C2 -100UF /16V
Y1 -4MHZ RESONATOR
D1-4 -1N4007 DIODE (4NOS)
L1 -5MM OR 3MM GREEN LED
U1 434/315MHZ ASK
U2 PIC16F628 PRE PROGRAMED MICRO
U3 HT12E RF DCODER
U4 LM805 5V VOLTAGEREGULATOR
2NOS 18 PIN IC SOCKET
RELAY DRIVERS (PCB3)
R1 -8 1K (8NOS)
L1-8 5MM/3MMLED (8NOS)
U1 ULN2803 RELAY DRIVERS
RL1-8 12V SPDT RELAY (PCB MOUNT)
1NOS 18 PIN C SOCKET