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This circuit using a dual-timer NE556 can produce 1Hz pulses spaced 5 seconds apart, either manually or automatically. IC NE556 comprises two independent NE555 timers in a single package. It is used to produce two separate pulses of different pulse widths, where one pulse initiates the activation of the second pulse. The first half of the NE556 is wired for 5-second pulse output. When slide switch S2 is in position ‘a’, the first timer is set for manual operation, i.e. by pressing switch S1 momentarily you can generate a single pulse of 5-second duration. When switch S2 is kept in ‘b’ position, i.e. pins 6 and 2 are shorted, timer 1 in NE556 triggers by itself. The output of the first timer is connected to trigger pin 8 of second timer, which, in turn, is connected to a potential divider comprising resistors R4 and R5. Resistor R1, preset VR1, resistor R2, preset VR2, and capacitors C2 and C5 are the components determining time period. Presets VR1 and VR2 permit trimming of the 5-secon...

Introduction  Purpose of a communication system: convey information through a medium or communication channel. ◊    The information is often represented as a baseband signal, i.e. a signal whose spectrum extends           from 0 to some maximum frequency. ◊     Proper utilization of the communication channel often requires a shift of the range of baseband         frequencies into other frequency ranges suitable for transmission, and a corresponding shift back to     the original frequency range after reception. ◊    A shift of the range of frequencies in a signal is accomplished by using modulation, which is             defined as the process by which some characteristic of a carrier is varied in accordance with                 modulating (signal) ◊      A common form of the carrier is a sinusoidal wave, in which c...