PRESENTED BY ARUN KUMAR .M BALA VINAYAGAM.K ELANTAMILAN with a modulating signal which typically contains information to be transmitted. What is demodulation? Demodulation is the process of eliminating the Carrier signal and recovering the base band message signal from the modulated signal is termed as Demodulation. . called the carrier signal.What is modulation? Modulation is the varying one or more properties of a high-frequency periodic waveform. . the modulation is applied continuously in response to the analog information signal.TYPES OF MODULATION In ANALOG modulation. In DIGITAL MODULATION. an analog carrier signal is modulated by a discrete signal. . the time is controlled by one external resistor and capacitor. and the output circuit can source or sink up to 200mA or drive TTL circuits. In the time delay mode of operation. . The circuit may be triggered and reset on falling waveforms.IC555 TIMER The LM555 is a highly stable device for generating accurate time delays or oscillation. the free running frequency and duty cycle are controlled with two external resistors and one capacitor. For astable operation as an oscillator. INTERNAL BLOCK DIAGRAM OF IC555 . Normally on and normally off output Available in 8-pin MSOP package. Temperature stability better than 0. . Output and supply TTL compatible.005% per ˚C. Adjustable duty cycle. Operates in both astable and monostable modes. Timing from microseconds through hours. Output can source or sink 200 mA. APPLICATIONS OF IC555 Precision timing Pulse generation Sequential timing Time delay generation Pulse width modulation Pulse position modulation Linear ramp generator . FSK is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave Frequency Shift Keying Modulated signal is obtained using IC 555 Timer The standard digital data input frequency is usually 150Hz When the input is HIGH i.when the input binary data is of logic 1.e. . the PNP transistor Q is off and IC 555 Timer works in the normal astable mode of operation. FSK MODULATION AND DEMODULATION USING IC555 . the "1" is called the mark frequency and the "0" is called the space frequency. With BFSK scheme. .GENERATION OF FSK Digital information is transmitted through discrete frequency changes of a carrier wave. The time domain of an FSK modulated carrier is illustrated in the figures to the right. SOFTWARE IMPLEMENTATION OF THE CIRCUIT . The demodulator receives a signal at one of the two distinct carrier frequencies 1. . The comparator prevents the amplitude changes occurring at the output stage.270 Hz or 1.the process of demodulation is achieved using Phase Locked Loop (PLL) IC 565. An input at frequency 1.070 Hz drives the demodulator output voltage to a more positive voltage level.070 Hz. The most important parameter that defines the efficiency of the modem is the probability of error and bit error rate. BER means the amount of eror introduced in the transmited signal by the channel’s noise. The expression for probability of error for this wireless data modem which uses non coherent FSK demodulation is given as Pe=1/2*exp(-Eb/(2*N0)) . SNR improvement of FSK over AM is approximately 3 to 4 dB. . Noise is eliminated in fsk reception. FSK may be satisfactory at nominal power. The power ratio (fsk versus AM) would become infinite in such a case.ADVANTAGES OF FSK MODULATION It rejects unwanted signals (noise) Automatic volume control methods may be used to minimize the effects of signal fading. APPLICATIONS OF FSK MODULATION Telephone-line Caller modems ID Micro computers Audio cassettes Radio control Emergency Alert System shortwave radio station . 90 94 / P 480 8 023. 5407 P %0 5407 7.981.80 P 9 .90/ 3 18 70. . -0 :80/ 94 2320 90 0110.390/ 83.98 :3.98 41 83.8 3480 P :942.9 3423. .43974 2094/8 2.94 18 . -0 8.07 8 .55742.02039 41 $ 4. 1.947 ..078:8 4:/ -0.' % $ $ &% 700.9../3 P $ # 2574.05943 P $ 2.420 31390 3 8:. .4:20 . /489..07 ./4..425:9078 :/4.943 .07.74.43974 20703.8809908 #.!!% $ $ &% %005430 3024/028 .079$8902 8479.