4013 pairs of D-type flip-flop in the astable multivibrator is used as a binary divider output, will produce the output frequency of the multivibrator frequency symmetrical hal

As shown, the circuit consists of a dual time base circuit 556 consisting of two synchronized multivibrator, two output clock

This self-build project can simulate a telephone call / connection between any two local telephone devices. This for a fraction of the outlay of some commercial units, many with cost-increasing features that usually are not required. The circuit is centred on two cascaded binary counters clocked by a 555 astable multivibrator. Several of the counters` outputs provide the frequencies, tones and time delays required. A pair of operational amplifiers detect on / off hook conditions at both ends of the simulated line. To detect call answering, a third op-amp monitors the ringing current. R/S latches and logic gates provide event storage and signal control. Discrete circuits provide the voltage multiplication and DC to AC conversion required for the ringing signal. A pair of miniature relays, switch each end of the simulated line between connection and ringing.

The schematic for a monostable multivibrator is shown in figure 3-11. Like the astable multivibrator, one transistor conducts and the other cuts off when the circuit is energized.

This simple CPO is for those who want to practice Morse Code in a different way, ie with out the morse key. It can be also used as a touch operated door bell. The popular timer IC555 is wired as astable multivibrator. The frequency (tone) can be changed by varying the 100 K variable resistor between pin 7 and 6 of timer IC555. The volume can be changed by varying the 10 K variable resistor and the sensitivity of touch plate can be controlled by adjusting the 1 K Ohms preset at pin 4 of IC555. The touch plate is connected to the base of transistor BC147B.

The Astable Multivibrator, which is generally used as a signal generator, is once again used here to generate the desired frequencies. It is an excellent example of the fact, how versatile simple basic electronic circuit can be. It seems quite obvious then, that by creating these insects frequencies electronically, we should be able to repel these insects! The most important point to remember here is that, unfortunately, this method has so far not been completely sucessfull. Whereas one group of insects can be made to run away at frequencies around 5 KHz, other types may desert only at higher frequencies, about 10 to 20 KHz. For some types, all the frequencies may fall on deaf ears! Yet other theories propose that in fact some frequencies may even attract them instead of repelling.

This circuit provides a digital square wave that can be viewed directly or used to drive other circuits. It used the CMOS 4047 Low-Power Monostable/Astable Multivibrator. As used in Tom Duncan's Adventures with Digital Electronic's Book, to drive CMOS Decade of 4-bit binary counters.

This circuit is basically simple and easy to build, it uses two transistors as active components and a few passive components like resistors, capacitors and two LEDs. The circuit makes use of the MPS2222 transistor. You can use any NPN type transistor as the basis of your circuit provided that, the transistors Emitter-Base Voltage is less than 12V and has a maximum value of 5V.

The MC74HC04 IC is a low cost CMOS Hex Inverter. I used this type mainly because, it is what I have, although you can use LS type but, with a little modification or exemptions..

This is a variation on the astable multivibrator. Circuit was recently developed to test for N-mosfets(the power kind e.g irf830). I don?t claim circuit can test all bad mosfets or all fault mosfet conditions. If mosfet is working it will operate in the astable multivibrator circuit causing the Led to flash. A bad mosfet will not cause the LED to flash. Below is the circuit diagram, the other half of the astable utilizes an npn transistor to make the circuit cheap. Almost any npn transistor will work in this circuit. The npn transistor to the right is used as a common emitter buffer that also drives the led as it receives pulses from the mosfet drain.

The tool is based on a NE555 (or LM555) timer i.c., wired as an astable multivibrator. The frequency of the multivibrator is determined by the value of the unknown capacitor Cx. The circuit can be fed by a small battery. I use myself a 9 V block battery which is connected to pins 4 and 8 of the i.c. via an on/off switch. The output of the multivibrator is connected to the digital frequency counter. The counter should assess the cycle length of the square wave, not the frequency (on most frequency counters, one can select either frequency measurement or measurement of the cycle length). A wave with a frequency of 1 kHz (i.e. 1000 Hz) has a cycle length of 1 millisecond.

Here is the circuit diagram of simple but highly effective TV remote jammer circuit. Most of the TV remotes have 38KHz operating frequency. A flood of IR beams in the same frequency can easily confuse the TV receiver and this is the operating principle of our jammer. The circuit is nothing but an astable multivibrator based on NE555 IC. The output of NE555 is amplified using a PNP transistor SK100 to drive the IR LEDs. Not only TV remotes, but any IR remotes operating in the 38KHz frequency region can be also jammed by using this circuit.

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.

One of the unusual features of the out-of-production Programmable Drum Set was its use of touch switches for control. Like most touch switches, these detect the difference in the capacitance of a plate when it is being touched by a finger versus the parasitic capacitance of the plate alone. The capacitance added by touching the plate is detected using a square wave oscillator. In the diagram below IC1:A and IC1:B, two gates from a 4001 CMOS Quad NOR IC, form an astable multivibrator with a 50kHz frequency as determined by the time constant of R2 and C2. The square wave output is buffered by IC1:C and used to drive a group of touch switches. Only two switch plates - TS1 and TS2 - are shown in the illustration, but in the PDS, 16 touch switches were excited by this one clock.

This is a simple LED flasher using two 2N3904 transistors. Classic astable multivibrator using 2 transistors. Transistor is not critical. Try these: 2N4401, 2N2222, NTE123A, NTE123AP, NTE159, TUP/TUN and those in your junk box, you may find that most of them will work. Obviously, the 470 ohm resistor determines the LED's brightness and limits the current flow to about 20mA. 390 ohm can also be used as a save value. If you decide to go with a green or yellow led, which draw more current, you may want to replace the 470 ohm with 270 or 330 ohm values.

This is basically a flasher circuit modified to turn on and off a bulb instead of a LED. It uses a 555 timer IC working as an astable multivibrator. The flashing rate can be varied from very fast to a maximum of once in 1.5 sec by varying the preset VR1.

The circuit presented here wakes you up with a loud alarm at the break of the daylight. Once again the 555 timer is used here. It is working as an astable multivibrator at a frequency of about 1kHz. The circuit's operation can be explained as follows: When no light falls on the LDR, the transistor is pulled high by the variable resistor. Hence the transistor is OFF and the reset pin of the 555 is pulled low. Due the this the 555 is reset.

This circuit produces a sound similar to a factory siren. It makes use of a 555 timer Ic used as an astable multivibrator of a center frequency of about 300Hz. The frequency is controlled by the pin 5 of the IC. When the supply is switched ON, the capacitor charges slowly and this alters the voltage at pin 5 of the IC hence the frequenct gradually increases. After the capacitor is fully charged, the frequency no longer increases.

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.

This circuit utilising a 555 timer IC can be used as an alarm system to prevent the theft of your luggage, burglars breaking into your house etc. The alarms goes ON when a thin wire, usually as thin as a hair is broken. The circuit is straightforward. It uses a 555 IC wired as an astable multivibrator to produce a tone of frequency of about 1kHz which gives out a shrill noise to scare away the burglar. The wire used to set off the alarm can be made of a thin copper wire like SWG 36 or higher. You can even use single strands of copper form a power cable.