MULTIVIBRATOR

Individual Sequential Logic circuits can be used to build more complex circuits such as Multivibrators, Counters, Shift Registers, Latches and Memories etc, but for these types of circuits to operate in a "sequential" way, they require the addition of a clock pulse or timing signal to cause them to change their state. Clock pulses are generally continuous square or rectangular shaped waveform that is produced by a single pulse generator circuit such as a Multivibrator

MULTIVIBRATOR

Sequential logic circuits that use the clock signal for synchronization are dependen upon the frequency and clock pulse width to activate there switching action. Sequential circuits may also change their state on either the rising or falling edge, or both of the actual clock signal as we have seen previously with the basic flip-flop circuits. The following list are terms associated with a timing pulse or waveform.

Active HIGH  -  if the state changes occur at the clock's rising edge or during the clock width

Active LOW  -  if the state changes occur at the clock's falling edge

Clock Width  -  this is the time during which the value of the clock signal is equal to one.

Clock Period  -  this is the time between successive transitions in the same direction, i.e., between two rising or two falling edges.

Clock Frequency  -  the clock frequency is the reciprocal of the clock period, frequency = 1/clock period

MULTIVIBRATOR

There are basically three types of clock pulse generation circuits:

Astable - A free-running multivibrator that has NO stable states but switches continuously between two states this action produces a train of square wave pulses at a fixed frequency. Monostable - A one-shot multivibrator that has only ONE stable state and is triggered externally with it returning back to its first stable state. Bistable - A flip-flop that has TWO stable states that produces a single pulse either positive or negative in value.

12_ClockMonostb555.lvw12_MultiV.lvwhttp://www.electronics-tutorials.ws/sequential/seq_3.html

Clock - Detak

A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency to provide a stable clock signal for digital integrated circuits.

In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronome to coordinate actions of circuits. (sinyal berbentuk pulsa)

MULTIVIBRATOR

Clock - Detak

Pin Name Purpose

1 GND Ground, low level (0 V)

2 TRIG OUT rises, and interval starts, when this input falls below 1/2 of CTRL voltage.

3 OUT This output is driven to approximately 1.7V below +VCC or GND.

4 RESETA timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. Overrides TRIG which overrides THR.

5 CTRL "Control" access to the internal voltage divider (by default, 2/3 VCC).

6 THR The interval ends when the voltage at THR is greater than at CTRL.

7 DIS Open collector output; may discharge a capacitor between intervals. In phase with output.

8 VCC Positive supply voltage is usually between 3 and 15 V.

MULTIVIBRATOR

Free Running Multifibrator untuk membangkitkan pulsa digital

5 V

M ultifib rator ja lan bebas(free running m ultifibra tor)

+ 5

0gnd

astabil

Pew aktu(tim m er)

555

4 8

7

6

2

3

1K

470K

1uF

+ 5

0gnd

5 V

MULTIVIBRATOR

Switch menggunakan saklar tekan…T ekan = tinggi

5 V

K eluaran

L epas = rendah

Saklarnorm aly off Perangkat disamping sebagai pembangkit

sinyal digital juga tidak diperkenanka, karena menyebabkan rangkaian terbuka pada saat saklar dilepas ( 0 V ≠ gnd )

Solusi

Tekanan saklar membangkitkan pulsa tembakan seperti pada gambar

5 V

M ultifib rator satu tem bakan(one shoot m ultifibra tor)

+ 5

0gnd

m onostabil

MULTIVIBRATOR

MULTIVIBRATOR

Bistabil - FF

Mode

operasi

Masukan Keluaran Pengaruh pada

keluaran QS R Q Q

Larangan 0 0 1 1 Larangan (don’t use)

Set 0 1 1 0 Me-set Q menjadi 1

Reset 1 0 0 1 Me-reset Q menjadi 0

Tetap 1 1 Q Q Tgt keadaan sebelumnya

S

R

Q

S

R

Q

set reset set reset