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, the charge-discharge cycles of the 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.
21.09.2014
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One of the simplest circuits in amateur radio electronics is an LED flasher on a single transistor. Its production can be done by any beginner who has a minimum soldering kit and half an hour of time.
Although the circuit under consideration is simple, it allows you to clearly see the avalanche breakdown of the transistor, as well as the operation of the electrolytic capacitor. Including, by selecting the capacitance, you can easily change the blinking frequency of the LED. You can also experiment with the input voltage (in small ranges), which also affects the operation of the product.
There are situations when you need a beacon circuit that would create really bright and noticeable flashes, for example, on a company car or a camping lantern.
Above is a diagram of such a beacon that flashes, creating a strobe effect.
The circuit is powered from a power source of at least 10 volts. To reduce the operating voltage, you can replace transistors VT1 and VT2 with transistors with the lowest voltage FE transition. And also by adjusting the values of resistors R1 and R2.
Resistors R3 and R4 regulate flashes; if you increase the resistor values to 100 Ohms, the LEDs will light up smoothly. Thanks to 1 Ohm resistors, the LEDs flash quickly, which creates a strobe effect.
Capacitors C1 and C2 regulate the flash frequency of LEDs VD1 and VD2. By reducing the capacitance of the capacitors you can increase the flash speed.
It is advisable to install brighter LEDs with greater luminous intensity.
As can be seen from the diagram, the device consists of two similar blocks, the first block consists of resistors R1 and R3, capacitor C1, transistor VT1 and LED VD1. The remaining details belong to the second block. By composing additional blocks you can increase the number of beacons.
Pay attention to the bases of transistors VT1 and VT2, they are not connected, this is not an error, and indeed the bases of the transistors in the device are not connected!
The device was mounted on a printed circuit board, the board was inserted into the relay housing, then it was tested and installed on a Niva company car in place of the standard dimensions, three LEDs were installed in each headlight. The device has been operating successfully for the second year, the components do not heat up, and no malfunctions have been recorded.
The device was developed more than a year ago, at the request of a friend, based on data taken on the Internet from open sources.
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad |
|---|---|---|---|---|---|---|
| VT1, VT2 | Bipolar transistor | KT315B | 2 | With any letter index | To notepad | |
| C1, C2 | Electrolytic capacitor | 1000 µF 16 V | 2 | To notepad | ||
| R1, R2 | Resistor | 1 kOhm | 2 | To notepad | ||
| R3, R4 | Resistor | 1 ohm | 2 | To notepad | ||
| VD1, VD2 | Light-emitting diode | 2 |
Flashing beacons are used in electronic security systems and on vehicles as indication, signaling and warning devices. Moreover, their appearance and “filling” are often not at all different from the flashing lights of emergency and operational services (special signals) - see fig. 3.9.
The internal “filling” of classic lamps is striking in its anachronism: here and there, beacons based on powerful lamps with a rotating cartridge (a classic of the genre) or lamps such as IFK-120, IFKM-120 with a stroboscopic device that provides flashes at regular intervals regularly appear on sale time (pulse beacons). Meanwhile, this is the 21st century, in which the triumphant march of super-bright (and powerful in terms of luminous flux) LEDs continues.
One of the fundamental points in favor of replacing incandescent and halogen lamps with LEDs, in particular in flashing lights, is the resource and cost of the LED.
By resource, as a rule, we mean failure-free service life.
The resource of an LED is determined by two components: the resource of the crystal itself and the resource of the optical system. The vast majority of LED manufacturers use various combinations of epoxy resins for the optical system, of course, with varying degrees of purification. In particular, because of this, LEDs have a limited resource in this part of the parameters, after which they “go cloudy”.
Various manufacturing companies (we won’t advertise them for free) claim a lifespan of their products in terms of LEDs from 20 to 100 thousand (!) hours. I categorically disagree with the last figure, since I have little faith that a separately selected LED will work continuously for 12 years. During this time, even the paper on which my book is printed will turn yellow.
However, it is quite obvious that the key to a long resource is ensuring the thermal conditions and power conditions of the LEDs.
In any case, compared to the life of traditional incandescent lamps (less than 1000 hours) and gas-discharge lamps (up to 5000 hours), LEDs are several orders of magnitude more durable.
The predominance of LEDs with a powerful luminous flux of 20-100 lm (lumens) in the latest industrial electronic devices, where they even replace incandescent lamps, gives radio amateurs a reason to use such LEDs in their designs.
Figure 3.9. Appearance of flashing lights
Thus, I am talking about replacing lamps for various purposes with powerful LEDs in emergency and special beacons. Moreover, with such a replacement, the main current consumption from the power source will decrease and will depend mainly on the current consumption of the LED used. For use in conjunction with a car (as a special signal, emergency light indicator and even a “warning triangle” on the roads), current consumption is not important, since the car battery has a fairly large energy capacity (55 A/h or more). If the beacon is powered by another power source (autonomous or stationary), then the dependence of the current consumption on the equipment installed inside is direct. By the way, the car battery can also discharge if the beacon is used for a long time without recharging the battery.
So, for example, a “classic” beacon for operational and emergency services (blue, red, orange, respectively) with a 12 V power supply consumes a current of more than 2.2 A. This current consists of taking into account the consumption of the electric motor of the rotating socket and the current consumption of the lamp itself. When a flashing pulse beacon is operating, the current consumption is reduced to 0.9 A. If, instead of a pulse circuit, you assemble an LED circuit (more on this below), the consumption current will be reduced to 300 mA (depending on the powerful LEDs used). The savings in detail are obvious.
The above data was established by practical experiments conducted by the author in May 2009 in St. Petersburg (a total of 6 different classic flashing lights were tested).
Of course, the question of the strength or, better yet, intensity of light from certain flashing devices has not been studied, since the author does not have special equipment (lux meter) for such a test. But due to the innovative solutions proposed below, this issue remains of secondary importance. After all, even relatively weak light pulses (in particular, from powerful LEDs) at night and in the dark are more than sufficient for the beacon to be noticed several hundred meters away. That's the point of long-range warning, isn't it?
Now let’s look at the electrical circuit of the “lamp substitute” of the flashing light (Fig. 3.10).
This multivibrator electrical circuit can rightfully be called simple and accessible. The device is developed on the basis of the popular integrated timer KR1006VI1, containing 2 precision comparators that provide an error in voltage comparison no worse than ±1%. The timer has been repeatedly used by radio amateurs to build such popular circuits and devices as time relays, multivibrators, converters, alarms, voltage comparison devices, etc.
The device includes, in addition to the integrated timer DA1 (multifunctional microcircuit KR1006VI1), a timing oxide capacitor C1, and a voltage divider R1R2. From the output of the DA1 chip (current up to 250 mA), control pulses are sent to the HL1-HL3 LEDs.
The beacon is turned on using switch SB1. The operating principle of a multivibrator is described in detail in the literature.
At the first moment of time, there is a high voltage level at pin 3 of the DA1 chip and the LEDs are lit. The oxide capacitor C1 begins to charge through the circuit R1R2.
After about 1 sec. (the time depends on the resistance of the voltage divider R1R2 and the capacitance of the capacitor C1) the voltage on the plates of this capacitor reaches the value necessary to trigger one of the comparators in the single housing of the DA1 microcircuit. In this case, the voltage at pin 3 of the DA1 chip is set equal to zero, and the LEDs go out. This continues cyclically as long as the supply voltage is applied to the device.
Rice. 3.10. Simple electrical circuit of an LED beacon
In addition to those indicated in the diagram, I recommend using high-power LEDs HPWS-TH00 or similar ones with a current consumption of up to 80 mA as HL1-HL3. Only one LED from the LXHL-DL-01, LXHL-FL1C, LXYL-PL-01, LXHL-ML1D, LXHL-PH01, LXHL-MH1D series manufactured by Lumileds Lighting can be used (all orange and red-orange).
The device supply voltage can be adjusted to 12 V.
The board with the elements of the device is installed in the housing of the flashing light instead of the “heavy” standard design with a lamp and a rotating socket with an electric motor. A view of the installed board with 3 LEDs is shown in Fig. 3.11.
In order for the output stage to have even more power, you will need to install a current amplifier on transistor VT1 at point A (Fig. 3.10), as shown in Fig. 3.12.
After this modification, you can use three parallel-connected LEDs of the types LXHL-PL09, LXHL-LL3C (1400 mA), UE-lf R803RQ (700 mL), LY-W57B (400 mA) - all orange.
If there is no power, the device does not consume any current at all.
Rice. 3 11 View of the LED beacon board installed in the standard flashing beacon housing
Those who still have parts of cameras with a built-in flash can go the other way. To do this, the old flash lamp is dismantled and connected to the circuit as shown in Fig. 3.13.
Using the presented converter, which is also connected to point A (Fig. 3.10), pulses with an amplitude of 200 V are received at the output of the device with a low supply voltage. The supply voltage in this case is increased to 12 V.
The output pulse voltage can be increased by connecting several zener diodes into the circuit, following the example of VD1, VD2 (Fig. 3.13). These are silicon planar zener diodes designed to stabilize voltage in DC circuits with a minimum current of 1 mA and a power of up to 1 W. Instead of those indicated in the diagram, you can use KS591A zener diodes.
Elements C1, R3 form a damping RC circuit that dampens high-frequency vibrations.
Now, with the appearance (in time) of pulses at point A (Fig. 3.10), the ELI flash lamp will turn on. Built into the body of the flashing light, this design will allow it to continue to be used if the standard beacon fails.
Fig 3.12 Connection diagram for additional amplifier stage
Option with flash lamp
Figure 3 13. Flash lamp connection diagram
Unfortunately, the life of a flash lamp from a portable camera is limited and is unlikely to exceed 50 hours. continuous operation in pulse mode. Battery charging and discharging control device for a miner's flashlight
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