LED beacon. LED flashing beacon Green and white/moon

The figure shows a diagram of an LED beacon, the circuit is simple and does not contain expensive elements, and is assembled according to the classical circuit (multivibrator).

The circuit consists of two transistors, two capacitors, four resistors, and two LEDs. The blinking frequency of the LEDs depends on the resistance of the 100K resistors and 10uF capacitors. Accordingly, by increasing the capacitance of the capacitors, the blinking frequency of the LEDs will decrease.

The LED beacon can be used as a Christmas decoration or just as an interesting toy.

Reference

The multivibrator is a relaxation signal generator of electrical rectangular oscillations with short fronts. The term was proposed by the Dutch physicist van der Pol, since there are many harmonics in the oscillation spectrum of a multivibrator - in contrast to a generator of sinusoidal oscillations ("monovibrator").

The multivibrator is one of the most common rectangular pulse generators, which is a two-stage resistive amplifier with deep positive feedback. In electronic engineering, a wide variety of multivibrator circuits are used, which differ in the type of elements used (tube, transistor, thyristor, microelectronic, and so on), mode of operation (self-oscillating, waiting for synchronization), types of connection between amplifying elements, methods for adjusting the duration and the frequency of the generated pulses, and so on.

The assignment of a multivibrator to the class of self-oscillators is justified only in the self-oscillatory mode of its operation. In standby mode, the multivibrator generates pulses only when synchronizing signals are received at its input. The synchronization mode differs from the self-oscillating one in that in this mode, with the help of an external control (synchronizing) oscillation, it is possible to adjust the multivibrator oscillation frequency to the frequency of the synchronizing voltage or make it a multiple of it (frequency capture) for self-oscillating multivibrators.

A symmetrical multivibrator is called when the resistances of resistors R1 and R4, R2 and R3 are equal in pairs, the capacitances of capacitors C1 and C2, as well as the parameters of transistors VT1 and VT2.

The circuit can be in one of two unstable states and periodically switches from one to the other and back. The transition phase is very short due to the positive feedback between the gain stages.

Operating principle

State 1: VT1 is closed, VT2 is open and saturated, C1 is quickly charged by the base current of VT2 through R1 and VT2, after which, when C1 is fully charged (the charge polarity is indicated in the diagram), no current flows through R1, the voltage at C1 is (VT2 base current) * R2, and on the VT1 collector - power.

The voltage at the collector VT2 is low (drop across a saturated transistor).

C2, charged earlier in the previous state 2 (polarity according to the scheme), begins to slowly discharge through the open VT2 and R3. Until it is discharged, the voltage at the base VT1 \u003d (small voltage on the VT2 collector) - (high voltage on C2) - that is, a negative voltage that tightly locks the transistor.

State 2: the same in mirror image (VT1 open and saturated, VT2 closed).

Transition from state to state: in state 1 C2 is discharged, the negative voltage on it decreases, and the voltage at the base of VT1 grows. After a fairly long time, it will reach zero. Having completely discharged, C2 begins to charge in the opposite direction until the voltage at the base of VT1 reaches approximately 0.6 V.

This will cause the opening of VT1, the appearance of a collector current through R1 and VT1, and a voltage drop across the collector of VT1 (a drop across R1). Since C1 is charged and cannot be discharged quickly, this leads to a voltage drop at the base of VT2 and the start of VT2 closing.

Closing VT2 leads to a decrease in the collector current and an increase in the voltage on the collector (a decrease in the drop across R4). In combination with a recharged C2, this further increases the voltage at the base of VT1. This positive feedback leads to saturation of VT1 and complete closure of VT2.

This state (state 2) is maintained during the discharge time of C1 through the open VT1 and R2.

Thus, the time constant of one arm is C1 * R2, the second - C2 * R3. This gives the duration of the pulses and pauses.

Also, these pairs are selected so that the voltage drop across the resistor under conditions of base current flowing through it would be large, comparable to power supply.

R1 and R4 are chosen to be much smaller than R3 and R2 so that charging the capacitors through R1 and R4 is faster than discharging through R3 and R2. The longer the charging time of the capacitors, the more flat the pulse fronts will be. But the ratios R3/R1 and R2/R4 must not be greater than the gains of the respective transistors, otherwise the transistors will not open fully.

It will become easier to find various objects and objects at night, including moving ones (for example, pets), if you attach an economical beacon to them, the description of which is given below: when it gets dark, it automatically turns on and starts to give light signals.

The beacon diagram is shown in fig. 1. In fact, this is an asymmetric multivibrator based on transistors of different structures VT2, VT3, which generates short pulses with an interval of several seconds. The light source is the emitting diode HL1, the light sensor is the phototransistor VT1.

The device works as follows. As can be seen from the diagram, the emitter-collector section of the phototransistor VT1, together with the resistors R1, R2, forms a voltage divider in the base circuit of the transistor VT2. During daylight hours, the resistance of this section is small, so the voltage at the emitter junction of the transistor VT2 is small, and it is closed. The transistor VT3 is also closed, since the bias voltage at its base, which depends on the collector current VT2, is zero. In other words, the multivibrator does not work and the current consumed by it does not exceed 2 ... 3 μA.

With the onset of darkness, when, due to a decrease in illumination, the resistance of the emitter-collector section of the phototransistor VT1 increases so much that the voltage drop across it reaches approximately 0.6 V, the transistor VT2 begins to open. An increase in the voltage drop across the resistor R4 created by its collector current leads to the fact that the transistor VT3 also starts to open. As a result, the voltage on its collector decreases and the capacitor C1 begins to charge. The charging current flows through the resistor R1, the emitter-collector section VT1 and the emitter junction of the transistor VT2, so the latter opens even more and its collector current grows, which leads to an even greater opening of the transistor VT3, etc. The process proceeds like an avalanche, and the HL1 LED is bright flashes.

As the capacitor C1 charges, the charging current decreases, and at some point the transistor VT2, followed by VT3, begins to close. This happens quickly, so the LED goes out abruptly. Next, the capacitor is discharged through the HL1 LED, resistor R5 and high-resistance resistor R2, and as soon as the voltage across it drops to a certain value, transistor VT2 will start to open again and the whole process will repeat. Due to the high resistance of the discharge circuit, the duration of discharging the capacitor is much longer than charging, so the interval between LED flashes reaches several seconds.

To make the flashes more visible, the device uses a super-bright LED. To minimize the supply voltage, the TLWR9622 LED (red glow) of the Y group was selected (forward voltage - 1.83.-.2.07 V). This allows you to keep the beacon working when the supply voltage drops to about 2.3 V.

All parts of the device are placed on a printed circuit board made of one-sided foil fiberglass, a sketch of which is shown in Fig. 2.

In addition to the transistors indicated in the diagram, KT361V, KT361G and KT315V, KT315G, as well as KT3107 (VT2) and KT3102 (VT3) series transistors with any letter index can be used in the beacon. LED HL1 - any super-bright red glow with the lowest possible forward voltage and, preferably, with a large radiation angle. You can use a super-bright LED and a white glow, but then you will have to increase the supply voltage (it must be at least 3.5 V). Capacitors C1, C2 - any oxide in a cylindrical case with a diameter of 5 mm (for example, the TK series from Jamicon), resistors - MLT, C2-33, P1-4. Switch SA1 - any small-sized.

To expand the angle of emission of the LED, you can attach a light-diffusing plastic cap (opaque or transparent with a corrugated surface) to it.

The beacon power battery can be made up of various galvanic or rechargeable cells. For example, if it is intended for installation on small moving objects, then it is convenient to use small-sized and lightweight disk elements of size 357A, in other cases it is advisable to use AAA finger-type elements with a larger capacity.

If all the parts are in good order and there are no installation errors, the beacon starts working immediately after the power is turned on - it is enough to close the phototransistor window with an opaque curtain. The required brightness of the flashes is achieved by selecting the resistor R5. The duration of the flashes depends on the resistance of the resistor R1 and the capacitance of the capacitor C1, and the pauses between them depend on the capacitance of the same capacitor and the resistance of the resistor R2.

To increase the detection range of the beacon, the number of LEDs can be increased, for example, up to four, by connecting them in series and placing them in the structure in such a way that they emit light in different directions. In this case, of course, the supply voltage must be increased to 12 V and the resistance of the resistors R1, R2 must be proportionally increased, and the resistor R5 must be selected according to the required brightness of the flashes.

Also often viewed with this scheme:

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Flashing beacons are divided into halogen and LED. In the first variant, a light pulse appears when voltage is applied to a halogen bulb, in the second case, a light pulse is generated by an LED. Recently, LED beacons using ultra-bright LEDs have become more widespread. Such beacons are more durable, highly reliable, provide a guaranteed bright light pulse and, at the same time, consume less energy. Flashing beacons for special equipment and LED beacons differ in the type of attachment, they are on a mechanical and magnetic base. In the first case, the automotive LED lamp is mounted on a platform and bolts, and in the second case, on a magnetic base that securely fastens the flashing LED beacon on the vehicle roof or other metal surface. The flashing beacon with a halogen lamp can work continuously for 4000 hours at a temperature difference from -50 °C to +50 °C. Flashing beacons of the FP series are made for operation in difficult conditions - for special and emergency equipment. Beacon shades are made of impact-resistant polycarbonate, and sealing is provided with a silicone gasket. In addition to this, rubber rings are included for attaching to the base of the beacon. An orange flashing beacon is used in special vehicles. You can buy lighting equipment at a wholesale price from us in Moscow.
You can see the full catalog of special signals and flashing beacons on the Okata website in the "" section.

Flashing beacons are used in electronic house security systems and on cars as indication, signaling and warning devices. Moreover, their appearance and “stuffing” often do not differ at all from flashing beacons (special signals) of emergency and operational services.

There are classic beacons on sale, but their internal “stuffing” is striking in its anachronism: they are made on the basis of powerful lamps with a rotating cartridge (a classic of the genre) or lamps of the IFK-120, IFKM-120 type with a stroboscopic device that provides flashes at regular intervals ( pulse beacons). Meanwhile, in the courtyard of the XXI century, when there is a triumphal procession of very bright (powerful in terms of luminous flux) LEDs.

One of the fundamental points in favor of replacing incandescent and halogen lamps with LEDs, in particular in flashing beacons, is a longer resource (uptime) and lower cost of the latter.

The LED crystal is practically “indestructible”, therefore the resource of the device determines mainly the durability of the optical element. The vast majority of manufacturers use various combinations of epoxy resins for its manufacture, of course, with varying degrees of purification. In particular, because of this, LEDs have a limited resource, after which they become cloudy.

Different manufacturers (we won't advertise them for free) claim the resource of their LEDs from 20 to 100 thousand (!) Hours. I hardly believe in the last figure, because the LED must work continuously for 12 years. During this time, even the paper on which the article is printed will turn yellow.

However, in any case, compared to traditional incandescent lamps (less than 1000 hours) and discharge lamps (up to 5000 hours), LEDs are several orders of magnitude more durable. It is quite obvious that the guarantee of a long resource is to ensure a favorable thermal regime and stable power supply to the LEDs.

The predominance of LEDs with a powerful luminous flux of 20 - 100 lm (lumens) in the latest industrial electronic devices, in which they work instead of incandescent lamps, gives reason for radio amateurs to use such LEDs in their designs. Thus, I bring the reader to the idea of the possibility of replacing various lamps in emergency and special beacons with powerful LEDs. In this case, the current consumption by the device from the power source will decrease and will depend mainly on the LED used. For use in a car (as a special signal, an emergency light indicator, and even an “emergency stop sign” on the roads), the current consumption is unimportant, since the car’s battery (battery) has a fairly large energy capacity (55 or more Ah or more). If the beacon is powered by an independent source, then the current consumption of the equipment installed inside will be of no small importance. By the way, the battery of a car without recharging can be discharged during prolonged operation of the beacon.

So, for example, the “classic” beacon of operational and emergency services (blue, red, orange, respectively) when powered from a 12 V DC source consumes a current of more than 2.2 A, which consists of the consumption of the electric motor (rotating the cartridge) and the lamp itself. During the operation of a flashing pulse beacon, the current consumption decreases to 0.9 A. If, instead of a pulse circuit, an LED is assembled (more on this below), the current consumption will be reduced to 300 mA (depending on the power of the LEDs used). The cost savings are also significant.

Of course, the question of the strength of light (or, better, its intensity) from various flashing devices has not been studied, since the author did not have and does not have special equipment (luxmeter) for such a test. But due to the innovative solutions proposed below, this issue becomes secondary. After all, even relatively weak light pulses (in particular from LEDs) passed through the prism of the inhomogeneous glass of the beacon cap at night are more than sufficient for the beacon to be noticed several hundred meters away. That's the point of early warning, isn't it?

Now consider the electrical circuit of the "lamp substitute" flashing beacon (Fig. 1).

This electrical circuit of the multivibrator can rightly be called simple and affordable. The device was developed on the basis of the popular integrated timer KR1006VI1, which contains two precision comparators, providing a voltage comparison error of 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, signaling devices, voltage comparison devices, and others.

The device, in addition to the integral timer DA1 (multifunctional microcircuit KR1006VI1), also includes a time-setting oxide capacitor C1, a voltage divider R1R2. C3 output chip DA1 (current up to 250 mA) control pulses are sent to the LEDs HL1-HL3.

The principle of operation of the device

The beacon is switched on using the switch SB1. The principle of operation of the multivibrator is described in detail in the literature.

At the first moment, there is a high voltage level at pin 3 of the DA1 chip - and the LEDs are on. The oxide capacitor C1 begins to charge through the circuit R1R2.

After about one second (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 operate one of the comparators in a single package of the DA1 microcircuit. In this case, the voltage at pin 3 of the DA1 microcircuit is set to zero - and the LEDs This continues cyclically as long as the supply voltage is applied to the device.

In addition to those indicated in the diagram, I recommend using powerful HPWS-T400 LEDs 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 by Lumileds Lighting (all in orange and red-orange glow).

The supply voltage of the device can be increased to 14.5 V, then it can be connected to the on-board car network even when the engine (or rather, the generator) is running.

Design features

The board with three LEDs is installed in the housing of the flashing beacon instead of the "heavy" standard design (lamps with a rotating cartridge and an electric motor).

In order for the output stage to have even more power, it will be necessary to install a current amplifier on the VT1 transistor at point A (Fig. 1), as shown in Fig. 2.

After such refinement, it is possible to use three parallel-connected LEDs of the types LXHL-PL09, LXHL-LL3C (1400 mA),

UE-HR803RO (700 mA), LY-W57B (400 mA) are all orange. In this case, the total current consumption will increase accordingly.

Flash lamp option

Those who have preserved the details of cameras with 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 Figure 3. Using the presented converter, which is also connected to point A (Figure 1), pulses with an amplitude of 200 V are obtained at the output of the device with a low supply voltage. Supply voltage in this case, unequivocally increase to 12 V.