Simple flasher for two LEDs

Virtually every novice radio amateur collected multivibrator transistors. This scheme does not require a large number of components and has a completely understandable principle for beginners. However, the work of the finished product, despite the simplicity, is quite interesting and fascinating. Especially if you include two different colored LEDs in the circuit.
Simple flasher for two LEDs
Similar flashers are used in many fields of human activity. The most striking example of the use of the scheme is electronic flashing beacons on a service vehicle (ambulance, police). Symmetric multivibrators based on the structure described below can also be found in other radio equipment, for example, in acoustic sirens and alarms. They are used in the simplest children's toys.

The device and the principle of operation

The scheme of the educational multivibrator, the stage-by-stage assembly of which is described below, consists of two transistors, capacitors and LEDs.Additionally, depending on the voltage of the used power source, current-limiting resistors are added to the design. The flashing light on two transistors works as follows. In the first phase, one of the transistors is in the open state, as the current from the symmetric arm of the multivibrator arrives at its base. Due to this, one LED is lit and the opposite capacitor is charging. At this point, the first phase of the cycle ends. Then, when the capacitor is fully charged, the current stops flowing through it. As a result, the transistor closes and the first LED goes out. Instead, the second flashes. This happens because the capacitor gives up the accumulated energy. This opens the second transistor and the LED lights up. At the same time, the opposite capacitor is charging. Then the cycle is repeated according to the algorithm described above.
Simple flasher for two LEDs

Required materials and radio components

To assemble a classic 12 V LED multivibrator with your own hands, you will need the following radio components:
  • KT361 transistors - 2 pieces (KT315 but you have to change the polarity of the power,capacitors and light-emitting diodes);
  • electrolytic capacitors with a capacity of 47-50 microfarads and a rating of 16 V - 2 pieces;
  • 3 V LEDs - 2 pieces (preferably multicolored);
  • 300 Ohm resistors - 2 pieces;
  • 27 kΩ resistors - 2 pieces;
  • wires for connecting parts.
  • Simple flasher for two LEDs
    To distinguish the KT361 transistors from the legendary KT315, just look at their marking. For those who need to build a multivibrator according to the above scheme, the letter is located in the middle of the case. At KT315 - in the corner. You can replace these parts with more modern analogs, for which it is enough to use special resources on the Internet. You can of course use KT315, but in this case the polarity of the power supply, capacitors, LEDs will need to be swapped. If there were no resistors with the indicated values ​​at hand, then you can take several pieces with less resistance. Combining them sequentially (as in the photos), we obtain the required parameters. Note that with a power source with a different voltage (9 V or 4.5 V) you will need parts with lessface value. Capacitors can be taken with a different capacity. This will directly affect the flashing frequency of the LEDs. The larger the capacitance, the lower the switching frequency. The value of the capacitors must necessarily be greater than the voltage of the power source used. Naturally, the successful assembly of the symmetric multivibrator circuit will also require a minimum set for soldering.

    Step-by-step assembly of the multivibrator

    First recommended collect all the necessary radio components and lay them on the table as shown in the diagram. If soldering is carried out on the board, then this step can be skipped. When assembling a multivibrator with a mounted installation, the sequence of actions will be as follows.
    Simple flasher for two LEDs
    Simple flasher for two LEDs
    Simple flasher for two LEDs
    Simple flasher for two LEDs
    First, the LEDs are connected to each other, and the main resistance of 27 kΩ is added to the circuit. This takes into account the polarity of the light sources.In classical light emitting diodes, a negative output can be seen by visual inspection of the element - inside it is significantly wider than positive. Between themselves soldered exactly "minus" legs. Resistors are mounted between the LEDs as shown in the photo. Next, the resistance of 300 Ohms is soldered to the positive leads of the LEDs. They are needed in order to limit the current and save the elements from burning. Next turn for electrolytic capacitors. It is worth remembering that they also have positive and negative conclusions. "Minus" can usually be seen on the body - it is marked with a light bar and the corresponding symbols. At this stage of the assembly, we need positive conclusions - they are soldered to resistances of 300 Ohms, as shown in the photo. The most complex details in this circuit (for beginners in radio amateurs) are transistors. To simplify installation and do not confuse anything, the elements are recommended to immediately expand as shown in the photo. The transistor of the left shoulder of the multivibrator is reversed by the letter mark up, and of the right shoulder - down.
    Simple flasher for two LEDs
    Simple flasher for two LEDs
    With this arrangement, the lower legs directed towards each other will be emitters. They need to be interconnected. The same section will be supplied with a “plus” sign. Next, connect the collectors of the transistors to the positive terminals of the capacitors. For convenience, it is recommended to appropriately bend the middle legs of the parts (for KT361, these are collectors). The final step will be to connect the bases of transistors with negative capacitors from the opposite shoulders of the multivibrator. Resistances that were previously mounted in the circuit (at 27 kΩ) are also supplied to the soldering points of these nodes. The bases of both transistors with this positioning will be on top, which will also facilitate the work with them.
    Simple flasher for two LEDs
    Simple flasher for two LEDs
    Now it remains only to connect the wires from the power supply.The positive terminal is soldered to the line of connection of the emitters of the transistors, and the negative - between the LEDs. When the power supply is turned on, the multivibrator should immediately start working without any additional adjustment.
    Simple flasher for two LEDs
    If the LEDs in the off state do not go out completely, then you can add a small current-limiting resistor to the beginning of the circuit. If the power supply is adjustable, it is enough to reduce the voltage a little and it will work.


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