Astable or free-running multivibrators have been used in home-built amateur radio equipment for many years. The basic circuit is a two stage amplifier with AC-coupled feedback from output to input. One transistor stage is on ( conducting current ) while the other is off ( not conducting current ) until the stages switch conducting states repeatedly at a specific frequency. The oscillation frequency is set by the resistor and capacitor values connected to the base terminal of each stage. This RC network determines how long the transistor stays in the off position. Presented are two projects which utilize astable multivibrators built using the ubiquitous 2N3904 BJT. The first project is a code practice audio-frequency oscillator while the second is a simple , no-frills electronic keyer for keying a transmitter. Either circuit would be a great first project to learn how to build circuits using Ugly Construction.

This circuit produces a sound similar to the police siren. It makes use of two 555 timer ICs used as astable multivibrators. The frequency is controlled by the pin 5 of the IC. The first IC (left) is wired to work around 1Hz. The 47uF capacitor is charged and discharged periodically and the voltage across it gradually increases and decreases periodically. This varying voltage modulates the frequency of the 2nd IC. This process repeats and what you hear is the sound remarkably similar to the police siren.

Here is a simple circuit which can be used for decoration purposes or as an indicator. Flashing or dancing speed of LEDs can be adjusted and various dancing patterns of lights can be formed. The circuit consists of two astable multivibrators. One multivibrator is formed by transistors T1 and T2 while the other astable multivibrator is formed by T3 and T4. Duty cycle of each multivibrator can be varied by changing RC time constant. This can be done through potentiometers VR1 and VR2 to produce different dancing pattern of LEDs.

This circuit uses three easily available 555 timer ICs. All three work as astable multivibrators. The first 555 has an on period and off period equal to 1 sec. This IC controls the on/ off periods of the other 2 555s which are used to flash two bulbs through the relay contacts. The flashing occurs at a rate of 4 flashes per second. The diodes are used to protect the 555 ICs from peaks. The relays should have an impedance greater than 50ohms i.e, they should not draw a current more than 200mA.

Using modulated rectangular waves of different time periods, The circuit presented here produces ringing tones similar to those produced by a telephone. The circuit requires four astable multivibrators for its working. Therefore two 556 ICs are used here. The IC 556 contains two timers (similar to 555 ICs) in a single package. One can also assemble this circuit using four separate 555 ICs. The first multivibrator produces a rectangular waveform with 1-second low duration and 2-second high duration. This waveform is used to control the next multivibrator that produces another rectangular waveform. A resistor R7 is used at the collector of transistor T2 to prevent capacitor C3 from fully discharging when transistor T2 is conducting.

What exactly is a multivibrator? I suppose one definition would be 'a circuit which has several states'. This will do for now, it's quite loose so leaves plenty to the imagination! Conventional multivibrators have only two stages and come in three flavours: astable (where neither state is stable and the circuit oscillates between the two states); monostable (where one state is stable, the other transient). And bistable, where the circuit can be flipped from state one to state two. The fact that it can be 'flopped' back again leads to another term 'flip-flop' - but you can call an astable an astable flip-flop! Then you can get tristables - and one circuit I shall introduce is a 'donkey simulator' where 3 transistors are combined to make 3 separate astable mulivibrators!

This window comparator generates an output pulse for each event that occurs within a specified window. That is, each output pulse signifies an input voltage pulse or level change that exceeds VREFLOW. but not VREFHIGH· The monostable multivibrators, IC2A and IC2B, produce a 10-l"s pulse at their Q output in response to a rising edge at their A input. Comparator IC1B produces a rising edge when the input exceeds VREF Low and comparator IC2A produces a rising edge when the in])ut exceeds VREFHIGH.·

You can obtain well over 360° of phase delay by cascading two monostable multivibrators. In a typical configuration, a single monostable multivibrator is used to introduce delay in a pulse train; the multivibrator triggers on each incoming pulse, provided it resets in time for the next pulse. Yet even when it resets in time, the single monostable multivibrator provides a maximum phase delay of less than 360°. However, with the cascaded-multivibrator approach, you can achieve 650° of phase delay by using an input-pulse spacing of 200 p.s for example, with the component values shown. Every input pulse will trigger the circuit while you adjust the phase delay throughout its available range.

For a lower parts count than the 2 transistor multivibrators, 2 LEDs can be alternately flashed with a 555 integrated circuit configured as shown in Schematic 2. I chose the combination of a 2K2 and a 47K resistor to determine the oscillation frequency along with the 10 uF capacitor connected to pins 2 and 6. You can practically change the (R Spee

Here is a simple circuit which can be used for decoration purposes or as an indicator. Flashing or dancing speed of LEDs can be adjusted and various dancing patterns of lights can be formed. The circuit consists of two astable multivibrators. One multivibrator is formed by transistors T1 and T2 while the other astable multivibrator is formed by T3

As we know its on chip multivibrator means with IC555 one can design astable, monostable, bistable multivibrators. Its main applications are to generate timings, clock waveform, generate synchronizing signals, square wave oscillator and many more. So here we are going to discuss some of the applications of IC555. But before that I will start with the basic theory. Here I shall

A lot of electronic circuits using NE555 timer IC Here is the circuit diagram of a police siren based on NE55 timer IC. The circuit uses two NE555 timers ICs and every of them are wired as astable multivibrators. The circuit will be powered from something between 6 to 15V DC and is fairly loud. By connecting an extra power amplifier at the output

Multivibrators, like the familiar sinusoidal oscillators, are circuits with regenerative feedback, with the difference that they produce pulsed output. There are three basic types of multivibrator, namely the Bistable Multivibrator, the Monostable Multivibrator and the Astable Multivibrator. A bistable multivibrator circuit is one in which both LOW and HIGH output states are stable.

This circuit produces a sound similar to the police siren. It makes use of two 555 timer ICs used as astable multivibrators. The frequency is controlled by the pin 5 of the IC. The first IC (left) is wired to work around 1Hz. The 47uF capacitor is charged and discharged periodically and the voltage across it gradually increases and decreases perio

Using modulated rectangular waves of different time periods, the circuit presented here produces ringing tones similar to those produced by a telephone. The circuit requires four astable multivibrators for its working. Therefore two 556 ICs are used here. The IC 556 contains two timers (similar to 555 ICs) in a single package. One can also assembl

Here is a simple circuit diagram of a simple musical horn using two NE555 ICs. Two ICs are wired as astable mutivibrators. The output of first multivibrator is given to the discharge (pin 7) of the second astable multivibrator. The combined effect of the astable multivibrators produces a musical tone at the output.

A lot of electronic circuits using NE555 timer IC are already published here and this is just another one. Here is the circuit diagram of a police siren based on NE55 timer IC. The circuit uses two NE555 timers ICs and each of them are wired as astable multivibrators. The circuit can be powered from anything between 6 to 15V DC and is fairly loud. By

Two multivibrators with different frequencies can be built using the NAND gates of a 4011 IC. If the output of IC1. B is positive with respect to IC1. C, LED D1 is on. As the levels of IC1. A and IC1. D are exactly opposite, D2 is always on when D1 is off, and the other way around. The two oscillators have different frequencies, which are determined by the values

On astable multivibrators, the duty cycle is usually fixed unless there`s a potentiometer in place, but even still with a diode in parallel with R2, you will only get a duty cycle less than 50%. Also, to ask a question in a new thread, youcan click here. I`ve only been dealing with electronics for about 2 years now. The other people on this forum are much more helpful. it becomes necessary to insert a diode in parallel with

Here is a simple circuit which can be used for decoration purposes or as an indicator. Flashing or dancing speed of LEDs can be adjusted and various dancing patterns of lights can be formed. The circuit consists of two astable multivibrators. One multivibrator is formed by transistors T1 and T2 while the other astable multivibrator is formed by T3