PRESENTED BY ARUN KUMAR .M BALA VINAYAGAM.
K ELANTAMILAN
What is modulation?
Modulation is the varying one or more properties of a high-frequency periodic waveform, called the carrier signal, 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.
TYPES OF MODULATION
In ANALOG modulation, the modulation is applied continuously in response to the analog information signal. In DIGITAL MODULATION, an analog carrier signal is modulated by a discrete signal.
IC555 TIMER
The
LM555 is a highly stable device for generating accurate time delays or oscillation. . In the time delay mode of operation, the time is controlled by one external resistor and capacitor. The circuit may be triggered and reset on falling waveforms, and the output circuit can source or sink up to 200mA or drive TTL circuits.
For astable operation as an oscillator, the free running frequency and duty cycle are controlled with two external resistors and one capacitor.
INTERNAL BLOCK DIAGRAM OF IC555
Timing
from microseconds through
hours. Operates in both astable and monostable modes. Adjustable duty cycle. Output can source or sink 200 mA. Output and supply TTL compatible. Temperature stability better than 0.005% per C. Normally on and normally off output Available in 8-pin MSOP package.
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.e.when the input binary data is of logic 1, the PNP transistor Q is off and IC 555 Timer works in the normal astable mode of operation.
FSK MODULATION AND DEMODULATION USING IC555
GENERATION OF FSK
Digital
information is transmitted through discrete frequency changes of a carrier wave. With BFSK scheme, the "1" is called the mark frequency and the "0" is called the space frequency. The time domain of an FSK modulated carrier is illustrated in the figures to the right.
SOFTWARE IMPLEMENTATION OF THE CIRCUIT
the
process of demodulation is achieved using Phase Locked Loop (PLL) IC 565. The demodulator receives a signal at one of the two distinct carrier frequencies 1,270 Hz or 1,070 Hz. The comparator prevents the amplitude changes occurring at the output stage. An input at frequency 1,070 Hz drives the demodulator output voltage to a more positive voltage level.
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 channels 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))
ADVANTAGES OF FSK MODULATION
It
rejects unwanted signals (noise) Automatic volume control methods may be used to minimize the effects of signal fading. 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.
APPLICATIONS OF FSK MODULATION
Telephone-line Caller
modems
ID Micro computers Audio cassettes Radio control Emergency Alert System shortwave radio station
