# Bistable Multivibrator using 555 Timer

Individual Sequential Logic circuits can be used to make complex circuits like Counters, Latches, Shift Registers, or Memories etc, but for these kinds of circuits to function in a “Sequential” way, they need the count of a clock pulse to cause them to modify their state. Generally, Clock (CLK) pulses are square formed waves that are generated by a single pulse generator circuit like a Multivibrator which fluctuates between two states namely a “HIGH” and a “LOW”. There are basically three types of pulse generation circuits based on the number of stable states namely astable, monostable and bistable multivibrator.

Bistable Multivibrator using 555 timers IC is the simplest mode, where Monostable multivibrator mode has two states namely stable and unstable state, Astable multivibrator mode has two states namely both the states are unstable. Here in Bistable mode also has two states but both the states are stable. Means it remains in the equal state that means either HIGH or LOW until an exterior trigger is applied; otherwise it waits in one of the two states until further notice. In bistable mode there is no RC network like the other two modes of 555, hence there are no equations and waveform. Bistable mode simply works as an FF (Flip-flop).

## Bistable Multivibrator using 555 Timer

A bistable multivibrator can be built with the most popular and also low-cost IC i.e, 555 Timer. Before going through the complete explanation of 555 timer IC bistable multivibrator circuit you should know about this IC. For that please refer these links to know more about this IC: 555 Timer – Pin Description & Applications.

### What is a Bistable Multivibrator?

Bistable Multivibrators are one kind of multivibrators which depend upon the exterior triggers so as to switch between their two acceptable stable states. These circuits are also called as Trigger Circuits or more popularly as FFs (Flip-Flops), shaping the fundamental building blocks of sequential digital systems. These circuits can be intended in different ways, say, for instance, they can make of transistors or 555 timers Ics or Op-Amps or along with passive components, the resistors. The following circuit designed using two NPN bipolar junction transistors (BJTs) namely Q1 and Q2 and four resistors such as RC1, RC2, R1, and R2.

### Bistable Multivibrator using 555 Timer Circuit

The required components of bistable multivibrator using 555 timer IC include IC 555, Resistors, Potentiometer, Capacitors, Diodes 1N 4148, D.C. Power supply, Function Generators, Oscilloscope, Connecting wires and Breadboard.

• Connect the circuit as per the given circuit diagram.
• Use resistors RA, RB, RL and capacitors C1, C2. Using the power supply place VCC.
• Connect the pin 3 (output terminal) to the oscilloscope in dc coupling mode.
• Give the power supply to the circuit.
• Connect the end F (SET) to ground temporarily. This will situate the Q output in the oscilloscope to a HIGH level. This state will be lastingly stable state and the process is called “SET”.
• Now connect the end G (RESET) to VCC temporarily. This will locate the Q output in the oscilloscope to a LOW level. This is called “RESET” operation.
• When you are done, turn-off the power to your new circuit.

#### Working of Bistable Multivibrator using 555 Timer

In these circuits, the output is stable in both the states. The states are activated using an exterior trigger but not like the monostable multivibrator, it does not come back to its unique state. Another trigger is required for this to occur. This process is related to a flip-flop. There is no RC timing network and therefore no intend parameters. This circuit can be used to design a bistable multivibrator.

The Pin2 and pin4 are a trigger and reset input pins that are held high through pull-up resistors while the pin6 (threshold input) is simply grounded. Thus configured, pulling the trigger for a moment to ground performs as a ‘SET’ and changes the pin3 (output pin) to Vcc (high state). Pulling the threshold i/p to supply performs as a ‘RESET’ and changes the output pin to GND (low state). No capacitors are necessary for a bistable configuration.

#### Applications of Bistable Multivibrator

Bistable Multivibrators have several applications like frequency dividers, as a storage device in computer memories or counters but they are most excellent used in circuits like Latches and Counter.

The bistable multivibrator is used in digital communications.It is also used for reversing to the supply to a given circuit at regular intervals.

Thus, multivibrators are very significant electronic devices, used in an ample range of applications. As seen above, they’re basically building blocks of electronics and began from simpler vacuum tubes.After all, we all have to found somewhere, and for accepting electronics, this is one of the best places you can start! Do let us know if you’d like to know more about these topics and feel free to ask us anything via the comments below! Here is a question for you, What is the function of a bistable multivibrator?