TEXT DATA TRANSMISSION THROUGH OPTICAL FIBRE USING CDMA TECHNLOGY
In this project data is send through IR LED’s. and received by photo diode. Then this diode is receive the data and display it on LED. LED works as a display device.
In this project we show that how we communicate between two microcontroller . In this project we transfer the data between two microcontroller using serial communication. We use LCD in both the transmitter and receiver circuit and display it on the lcd. In cdma transmission we always transmit a data with code. In this project we select a code with the DIP switches. After selecting a code we transfer the data using send switch. Data it converted into light with the help of the op-amp amplifier circuit. Output of the amplifier is connected to the light and this light is connected to the input of the optical fibre. Data through optical fibre is connected to the receiver end. In the receiver end we receive the data on the photodiode and then connected to the receiver microcontroller and then display it on the lcd receiver. In this project we use two receiver circuit . We use two receiver circuit because we want to show multiple Rx circuit. Receiver circuit receive the message when only code is match. Then buzzer is on and lcd display data received and then lcd display a same ASCII data of transmiiter end. .
Pin no 40 of the ic is connected to the positive supply. In this project we use ic 7805 as regulator to stablize the voltage to 5 volt DC. In this project we use 9 volt DC as a main power source. With the help of the regulator we stablize the voltage to the 5 volt DC. Pin o 31 is also connected to the positive supply. Pin no 18 and 19 is connected to the crystal with two capacitor. In this project we use 12 Mhz crystal for outer frequency. All the input switches are connected to the port P1. All the switches are for alphanumeric data generation. We used mirco switches for keys purpose. One point of each key is connected with microcontroller and other point of each key is connected with ground .ie. each time when we press key then we provide ground that pin of microcontroller. To generate multifunction from each key i.e. a,b and c, we will give delay to keys. If switch will pressed for delay then mcu will change the ‘a’ to ‘b’ and then after more delay it will move ‘b’ to ‘c’. Similarly we can different characters from same key by adding delay. We will use 16*2 LCD ( universally called 44780 standard LCD) .
for amplification purpose we will use voltage and power amplifier. First of all we will use voltage amplifier. For that purpose we will use op amp 741 ic.first pin and 5pin of this ic will not be connected . we will give output from microcontrollers 11th pin to 2nd pin of iC741.3rd pin of mcu will be connected with null resistors. One 10k ohm resistance w.r.t ground and one 10k ohm resistance w,r,t vcc will be connected with 3rd pin IC741. IC 741 will connected with mcu at pin 2 of 741 using a coupling cap .1µf and resistance. Then 7 pin of 741 will be connected with vCC and 4 th pin will be grounded. Output of voltage amplifier will be rom 6th pin . Output of 741 will be connected with emitters of transistors 548 and 558. Tr 548 is npn transistors and tr558 is pnp transistors.we will connect AGC 10k pot from o’p of emitters of tr to 2pin of IC741. then we will convert the electric signal to ir will ir led. On rxer end we wil get the signalat pin no 10 of mcu after rxing from photo diode. We will use 4bit cod switches so that we can show that each time we will change code it will be transmitted only if code it mactches with the rxer code. If code matches only then it wil display “ data rxed” if not it will not play anything on LCD display. Then we will press enter switch . after preesing it will display “ eneter the password’ on rxer LCD display. Then we wil enter three no password from micro switches connected with rxer mcu. Then iif code matches it will display data on rxer side. In this way we are entering security for owner of rxer. So that only owner can read data rexed.
This project include
serial communication- sbuf
alphanumeric keyboard interfacing
Chip to chip data communication
In this connected to ground pin for providing a low voltage signal to microcontroller.
In this project we will generate multi character from same key using microcontroller assembly programming. We will give delay for that purpose. If key will be pressed for some time then mcu will move one character to other. If still key pressed for moiré delay then mcu will change the character to third option. In this way 1st key will change char from ‘a’ to ‘b’ to ‘c’. so its very important according to advanced keyboard interfacing point of view.
Our program sense this pins and then acknowledge this and call a lcd write function on every switch
IN this program we monitor the switch with the help of the JNB command and then jump to the switch location of JNB command offer
Here Txdata is Port P1 , we monitor this pin by JNB command if the pin is low, when we press a switch then pin gets low then our program jump to the cho function. So by this way we monitor the different switches one by one
In this project we assigne each switch for different letter. Like switch p1.0 is for a A character. So we move the ASCII code of A into a Accumulator and then call a write_m function.
Each switch is for the different letter. In this project we use total 6 switches from A, b,c,d,f,g.
In this project we use only 6 switches, but in future it is possible to use 26 switches for keyboard . then we use multipal switches with the help of row and matrix logic.
‘a’ with semicolon is ASCII code data assembler automatic comvert it in to a hex code automatically. Whenever we want to write something in the lcd then we use Accumulator to receive a data.
After sensing all the switches for different codes we jump to MAIN program for further procedding. Whenever we press a switch then after putting a value in the A then we call a LCD write message.
Whenever we want to write a message in the in the LCD then set the RS bit of LCD by set b command and clr the R/W pin. Enable pin is also very important for the enable firstly we clr the E and then Set the e pinAfter write in the lcd then we monitor the send switch when send switch is pressed then we call a transmit switch
MOV A,CODE ;SEND ADDRESS
;TRANSMIT DATA SERIALLY
LCD is connected to the port p0 of the microcontroller. Port p0 is open collector mode port so to get a data from this pin we connect a pull resistor on each pin. So we connect a 10 k ohm resistor to all the eight pins of port p0. Control pins of the lcd is connected to the p2.5,p2.6, p2.7 . Output is available from the pin p3.1. which is transmit pin of the microcontroller. Output from the microcontroller is connected to the op-amp amplifier circuit, Here in this project we use ic 741 as a amplifier. Pin no 7 is connected to the positive line and pin no 4 is connected to the negative pin. Pin no 2 is input pin data from the microcontroller is connected to the pin no 2of the ic 741. Pin no 3 is act as a reference pin, so we connect a two 10 k ohm resisitor to this pin. With the help of these two resistor we provide a zero voltage to this pin.
P2.0, P2.1,p2.2,p2.3 is connected to the four bit code.
Send switch is connected to the p3.2
Data with code is transmit through a optical fibre and then connected to the photodiode fo the receiver circuit. Photodiode receive the signal on p3.0 and display on the lcd on the receiver end if the code is match. In the receiver circuit Pin no 40 and 31 is again connected to the positive pin. Pin no 20 is connected to the ground pin. Port 0 with 10k pull up resistor is connected to the data lines of the lcd. Three control pins are connected to the p2.5, p2.6, p2.7 of the microcontroller..Receiving buzzer is connected to the p3.2 of the microcontrollerWhenever controller receive the message and code is match then circuit gives a buzzer sound . lcd display a message received.