Flashing LEDs are often used in various signal circuits. Light emitting diodes (LEDs) of various colors have been on sale for quite a long time, which blink periodically when connected to a power source. No additional parts are needed to make them blink. A miniature integrated circuit that controls its operation is mounted inside such an LED. However, for a novice radio amateur it is much more interesting to make a flashing LED with your own hands, and at the same time study the principle of operation of an electronic circuit, in particular flashers, and master the skills of working with a soldering iron.
There are many schemes that can be used to make an LED blink. Flashing devices can be made either from individual radio components or based on various microcircuits. First, we will look at the multivibrator flasher circuit using two transistors. The most common parts are suitable for its assembly. They can be purchased at a radio parts store or “obtained” from obsolete televisions, radios and other radio equipment. Also in many online stores you can buy kits of parts for assembling similar circuits of LED flashers.
The figure shows a multivibrator flasher circuit consisting of only nine parts. To assemble it you will need:
It is not necessary that paired parts, for example resistors R2 and R3, have the same value. A small spread in values has virtually no effect on the operation of the multivibrator. Also, this LED flasher circuit is not critical to the supply voltage. It works confidently in the voltage range from 3 to 12 volts.
The multivibrator flasher circuit works as follows. At the moment of supplying power to the circuit, one of the transistors will always be open a little more than the other. The reason could be, for example, a slightly higher current transfer coefficient. Let transistor T2 initially open more. Then the charging current of capacitor C1 will flow through its base and resistor R1. Transistor T2 will be in the open state and its collector current will flow through R4. There will be a low voltage on the positive plate of capacitor C2, connected to the collector T2, and it will not charge. As C1 charges, the base current T2 will decrease and the collector voltage will increase. At some point, this voltage will become such that the charging current of capacitor C2 will flow and transistor T3 will begin to open. C1 will begin to discharge through transistor T3 and resistor R2. The voltage drop across R2 will reliably close T2. At this time, current will flow through the open transistor T3 and resistor R1 and LED1 will light up. In the future, charge-discharge cycles of capacitors will be repeated alternately.
If you look at the oscillograms on the collectors of the transistors, they will look like rectangular pulses.
When the width (duration) of rectangular pulses is equal to the distance between them, then the signal is said to have a meander shape. By taking oscillograms from the collectors of both transistors at the same time, you can see that they are always in antiphase. The duration of the pulses and the time between their repetitions directly depend on the products R2C2 and R3C1. By changing the ratio of products, you can change the duration and frequency of LED flashes.
To assemble the blinking LED circuit, you will need a soldering iron, solder and flux. As a flux, you can use rosin or liquid soldering flux, sold in stores. Before assembling the structure, it is necessary to thoroughly clean and tin the terminals of the radio components. The terminals of the transistors and the LED must be connected in accordance with their purpose. It is also necessary to observe the polarity of connection of electrolytic capacitors. The markings and pin assignments of KT315 transistors are shown in the photo.
Most LEDs operate at voltages above 1.5 volts. Therefore, they cannot be lit in a simple way from one AA battery. However, there are LED flasher circuits that allow you to overcome this difficulty. One of these is shown below.
In the LED flasher circuit there are two chains of capacitor charging: R1C1R2 and R3C2R2. The charging time of capacitor C1 is much longer than the charging time of capacitor C2. After charging C1, both transistors open and capacitor C2 is connected in series with the battery. Through transistor T2, the total voltage of the battery and capacitor is applied to the LED. The LED lights up. After the discharge of capacitors C1 and C2, the transistors close and a new cycle of charging the capacitors begins. This LED flasher circuit is called a voltage boost circuit.
We looked at several LED flashing light circuits. By assembling these and other devices, you can not only learn how to solder and read electronic circuits. As a result, you can get fully functional devices useful in everyday life. The matter is limited only by the imagination of the creator. With some ingenuity, you can, for example, make an LED flasher into a refrigerator door open alarm or a bicycle turn signal. Make the eyes of a soft toy blink.
Hello everyone, today we will look at a flasher using a single transistor. You can say these are the first steps in radio electronics, because the first thing I decided to assemble was a transistor flasher. The circuit is very simple and consists of four parts: an n-p-n conductivity transistor (if you don’t know, search on Google, read what kind of thing it is) in my case it was bc547, an electrolytic capacitor of 470 uF (microfarads), a 1.8 kilo-ohm resistor and a green LED .
It is not so easy to assemble - you need to know where the plus and minus are at the LED and capacitor. The polarity of the LED is checked by connecting it to a 5-10 volt power source through a 100 Ohm resistor.
The capacitor is simpler, since on the body there is a white, yellow, blue line - on that side it has a minus, and on the other side it has a plus.
It’s better to look up the pinout of the transistor you are using on the Internet, in my case it’s like this:
We learned something about radio components, now let’s look at the circuit. There is nothing complicated about it. Let's start soldering. We clean the soldering iron tip from dirt and oxide.
Now let's look at the parts that I desoldered from the boards. To identify the resistance value, use .
Then we solder the capacitor, carefully look at the pinout of the transistor and the polarity of the LED and capacitor. The resistor has no polarity - it can be soldered on either side.
Our device is assembled. We solder the wiring and test it, the operating voltage is 8-18 volts.
If you don’t have the opportunity to buy a ready-made flashing LED, where the necessary elements are built into the bulb to perform the desired function (all you have to do is connect the battery), try assembling your own circuit. You will need little: calculate the LED resistor, which together with the capacitor sets the oscillation period in the circuit, limit the current, select the type of switch. For some reason, the country's economy is driven by the mining industry; electronics are buried deep in the ground. I'm tense with the element base.
When connecting an LED, learn a minimum of theory - the VashTechnic portal is ready to help. The region of the pn junction, due to the existence of hole and electronic conductivity, forms a zone of energy levels unusual for the thickness of the main crystal. By recombining, charge carriers release energy; if the value is equal to a quantum of light, the junction of the two materials begins to radiate. The hue is determined by certain quantities, the relationship looks like this:
E = h c / λ; h = 6.6 x 10-34 is Planck’s constant, c = 3 x 108 is the speed of light, the Greek letter lambda denotes wavelength (m).
From the statement it follows: a diode can be created where the difference in energy levels is present. This is how LEDs are made. Depending on the difference in levels, the color is blue, red, green. Rare LEDs have the same efficiency. The blue ones, which historically appeared last, are considered weak. The efficiency of LEDs is relatively low (for semiconductor technology), rarely reaching 45%. The specific conversion of electrical energy into useful light energy is simply amazing. Each W of energy produces 6-7 times more photons than an incandescent filament under equivalent consumption conditions. Explains why LEDs have a strong position in lighting technology today.
Creating a flasher based on semiconductor elements is incomparably simpler. Relatively low voltages are enough, the circuit will start working. The rest comes down to the correct selection of key and passive elements to create a sawtooth or pulse voltage of the desired configuration:
Obviously, connecting an LED to a 230 volt network seems like a bad idea. There are similar circuits, but it is difficult to make it blink, the element base is missing. LEDs operate from much lower supply voltages. The most accessible are:
The design of the LED is clear, the combustion conditions are known, let's start implementing the idea. Let's make the element blink.
A computer power supply is an ideal option for testing SMD0603 LEDs. You just need to install a resistive divider. According to the technical documentation diagram, the resistance of p-n junctions in the forward direction is assessed, with the help of a tester. Direct measurement is not possible here. Let's put together the diagram shown below:
The +3.3 V wire of the computer power supply is orange insulated, we take the circuit ground from the black one. Please note: it is dangerous to turn on the module without load. Ideal to connect a DVD drive or other device. If you have the ability to handle live devices, it is permissible to remove the side cover, remove the necessary contacts from there, and do not remove the power supply. The connection of LEDs is illustrated by the diagram. Have you measured the resistance on the parallel connection of LEDs and stopped?
Let us explain: in working condition, you will need to turn on several LEDs; let’s do a similar setup. The supply voltage on the chip will be 2.5 volts. Please note that the LEDs are flashing and the readings are inaccurate. The maximum does not exceed 2.5 volts. Indication of successful operation of the circuit is expressed by blinking LEDs. To make the part flicker, remove the power from unnecessary ones. It is possible to assemble a debugging circuit with three variable resistors - one in a branch of each color.
You need to take significant values, and don’t forget: we will significantly limit the current flowing through the LEDs. In fact, you will need to think through the question according to the situation.
Flashing LED circuit
The circuit shown in the figure uses avalanche breakdown of the transistor to operate. KT315B, used as a key, has a maximum reverse voltage between the collector and base of 20 volts. There is little danger in such inclusion. For the KT315Zh modification, the parameter is 15 volts, much closer to the selected supply voltage of +12 volts. A transistor should not be used.
Avalanche breakdown abnormal mode of p-n junction. Due to the excess of the reverse voltage between the collector and the base, atoms are ionized by impacts of accelerated charge carriers. A mass of free charged particles is formed, carried away by the field. Eyewitnesses claim: for the breakdown of the KT315 transistor, a reverse voltage applied between the collector and emitter with an amplitude of 8-9 V is required.
A few words about the operation of the circuit. At the initial moment of time, the capacitor begins to charge. Connected to +12 volts, the rest of the circuit is broken - the transistor switch is closed. Gradually, the potential difference increases and reaches the avalanche breakdown voltage of the transistor. The capacitor voltage drops sharply, two open p-n junctions are connected in parallel:
In total, the voltage will be about 1 volt, the capacitor begins to discharge through the open p-n junctions, only the voltage drops below 7-8 volts, and your luck runs out. The transistor switch is closed, the process is repeated again. The circuit is inherent in hysteresis. The transistor opens at a higher voltage than it closes. Due to the inertia of processes. We see how the LED works.
The values of the resistor and capacitance determine the oscillation period. The capacitor can be taken much smaller by connecting a small resistance between the transistor collector and the LED. For example, 50 Ohm. The discharge constant will increase sharply, and it will be easier to check the LED visually (the burning time will increase). It is clear that the current should not be too large; the maximum values are taken from reference books. It is not recommended to connect LED lamps due to the low thermal stability of the system and the presence of abnormal transistor mode. We hope the review turned out to be interesting, the pictures are intelligible, and the explanations are clear.
Light-emitting diodes are widely used in a variety of fields.
Before you make a flashing LED yourself, you should take into account all the nuances of manufacturing such a lighting structure, as well as purchase high-quality materials and prepare a competent assembly diagram.
Such lighting devices are absolutely no different in size from the dimensions of a standard indicator LED, and the design of the device includes a semiconductor generator chip and several additional elements.
In addition to compactness, the advantages of ready-made illuminators are represented by a very wide range of supply voltages, a variety of emission colors and various flash frequencies, as well as high efficiency.
At the moment, there are several practical circuits that are quite accessible for independent implementation, which differ in the number and type of radio components.
The first circuit is characterized by the presence of a low-power, polar capacitor 16V - 470 μF, a resistor and an LED. Sufficient power supply for the device is provided by a standard 12V source. The principle of operation resembles an “avalanche breakdown,” and a noticeable disadvantage of such a circuit is represented by the need to use a special voltage source.
Schematic diagram of LED flashes
The second circuit is characterized by an assembly similar to a transistor multivibrator. This is what determines the high reliability of the device. The operating principle is based on the use of a pair of polar capacitors 16 V - 10 μF, a pair of limiting resistors (R1) and (R4), a pair of resistors (R2) and (R3), as well as a pair of light diodes.
The second circuit operates under conditions of a wide voltage range with serial and parallel connection of light diodes, and changing the capacitor capacitance allows you to obtain a multivibrator with different luminescence.
Modern LEDs can become a full-fledged replacement for incandescent lamps, which is due to the different characteristics of such light sources made on the basis of an artificial semiconductor crystal.
The main parameters of the LEDs are presented:
certain rules must be followed. Depending on the characteristics and type of power source, there are a couple of options for connecting the device to a 220V network: using a driver with a standard current limiter or using a special power supply that well stabilizes the voltage.
The assembly of structures based on several LED illuminators involves the use of series or parallel connection schemes.
On all radio components, the lead-out parts of the elements are cleaned and tinned. It is very important to consider polarity when connecting capacitors. The blinking of the light diode is ensured by the cyclic flow of current.
When all elements are correctly assembled, the manufactured lighting device has a blinking frequency of about one and a half Hz, or approximately fifteen flashes every ten seconds.
Simple sequential flashes are produced using a pair of C945 transistors or analog elements. In the first case, the collector is located in the central part, and in the second, the center is allocated for the placement of the base.
A pair of flashing LEDs and a circuit with one diode are assembled in accordance with the standard circuit. The blinking frequency is ensured by the presence of capacitors (C1) and (C2) in the circuit.
pn junction resistance diagram
If it is necessary to connect several LED elements at once, a PNP transistor of sufficient power is installed.
Flashing LEDs are obtained by connecting the leads to multi-colored elements, alternating pulses are provided by the built-in generator, and the blinking frequency directly depends on the installed program.
Flashing LED light sources, equipped with a standard built-in generator, are widely used in New Year's garlands.
It is the sequential assembly of such products, supplemented by an installed resistor that has a slight difference in nominal values, that makes it possible to achieve a shift in the blinking process of individual elements of the electronic circuit.
The result of this assembly is an original lighting effect, which does not require the addition of an overly complex control unit. Most often, the New Year's garland is connected using a conventional diode bridge.
Flashing diode current-controlled light emitters are in demand in a wide variety of modern household appliances and electrical equipment, where they play the role of standard indicators. At the same time, such indicator lights signal a certain state of the device or charge level. Based on blinking diodes, electronic displays, various advertising signs, all kinds of children's toys and many other products are assembled.
Flashing diodes are great for creating a huge number of interesting and unusual lighting effects, including a “traveling wave”.
Flashlights made using an LED light source are brighter and more economical. The power source is a 12 V battery. To make such a flashlight with your own hands, you need to purchase:
Homemade flashlight
Assembly work is carried out using a soldering iron, solder, a hacksaw and a needle file, sandpaper and side cutters.
After placing all the elements in the PVC pipe housing, the LED light source is installed, and fittings and a plug are installed to protect the lantern from moisture getting inside.
A flashlight assembled according to the circuit can be represented not only as a one-piece model, but also by connecting several AA or AAA batteries in series at once, which provides an optimal total voltage of 12 V.
One of the options for using solid-state light sources for decorative purposes is the assembly of so-called “running lights” on diodes, which includes a rectangular pulse generator, a counter, a decoder and display devices.
The assembly of all elements according to the proposed circuit is carried out on a prototype solderless board, and the installed capacitors and resistors at nominal values may have some spread, but strictly within ±20%.
with a thin tip, solder and rosin;
Step-by-step technology for self-assembly of a diode garland:
At the final stage, the 8-12V power supply and a standard resistor are connected.
When assembling a luminous garland yourself, you must remember that only the serial connection of all LEDs in the circuit according to the standard circuit allows you to obtain the traditional flickering effect.
The scope of application of flashing LEDs is currently quite wide. If you wish and have some knowledge in the field of electrical engineering, on the basis of such light sources it is quite possible to independently make various signal circuits, original children's toys, portable flashlights and even glowing New Year's garlands.
