Flashing LED with RF generator. Do-it-yourself pulse generator. High voltage pulse generator. Dual frequency oscillator with flashing LED

Electronic devices

S. RYUMIK, Chernihiv, Ukraine
Radio, 2000, No. 2

In the catalogs of foreign companies producing semiconductor devices and trading them, the so-called Blinking LED Lamps"- LEDs that look ordinary, but when connected to a constant voltage source, they flash and go out about twice a second. These devices can often be purchased on radio markets. This article describes several simple devices in which a "blinking" LED serves as a generator not only light and electrical impulses.

First of all, let's answer the question why is this LED blinking? Inside it, as shown in the diagram (Fig. 1), in addition to the actual light-emitting semiconductor structure HL1, there are a pulse generator and an electronic key. Sometimes a quenching resistor R1 is provided, in other cases, its functions are performed by the internal resistance of the key. Diode VD1 protects the device from supply voltage of reverse polarity.

By the way, it is this diode that causes the device to fail. It often happens that when checking an LED, a relatively powerful 9 V battery is connected to it with the polarity reversed. As a result, a current of hundreds of milliamps heats up the protective diode to a temperature that is dangerous not only for itself, but also for other components of the device. Therefore, when checking the LED in series with it, it is necessary to include a resistor with a resistance of 100 ... 200 Ohms. During operation, when the voltage applied to the LED has the correct polarity and is within acceptable limits, an additional resistor is not needed.

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The most common are "flashing" LEDs of the V621, V622, V623 series (Diverse); LTL 4213, LTL 4223, LTL 4233 (Lite On Opto); TLBG5410, TLBR5410, TLBY5410 (Temic Telefunken); L-36, L-56, L-616, L-796, L-816 (Kingbright Reinhold). In appearance, they resemble the usual AL307BM, they have a body with a diameter of 3 ... 10 mm, a viewing angle of 40 ... 1400, the color of the glow is red, orange, yellow or green. Their typical parameters are as follows: operating voltage - 3.5 ... 13 V, maximum forward current - 60 ... 70 mA, maximum power dissipation - 200 mW, flash frequency - 1.5 ... 2.5 (sometimes up to 5 Hz), brightness - 1.3 ... 1000 mcd.

In the luminous state, the properties of a "blinking" LED are similar to those of an ordinary LED. The experimentally taken initial segment of its current-voltage characteristic is shown in Fig. 2 (curve 1). In the intervals between flashes, the "LED" circuit is broken and, at the same voltage, the current flowing through the device is much less, since only the internal generator consumes it. Curve 2 corresponds to this state.

If a resistor is connected in series with the "blinking" LED, the voltage drop across it will change in time with the flashes. Using an oscilloscope, you can make sure that the generation continues even when the resistance of the resistor increases to a value at which flashes of light are no longer visible. Carried out in fig. 2 load line (3) corresponds to a resistor with a resistance of 33 kΩ and a supply voltage of 5 V. The difference in voltage drops across the resistor during flash and pause AU exceeds 2 V. This is enough, for example, to trigger a logic element.

Devices, the schemes of which are shown in fig. 3 and 4, by analogy with RC oscillators, one could call RHL oscillators. The types of LEDs and logic elements are not indicated in the diagrams, since a variety of combinations of them have been tested and work stably. The duration of the high logic level at the output is 280...320, low - 340...370 ms. These values within a small range depend on the resistance of the resistor R1 and the type of logic element used. In the device according to the scheme in Fig. 3, the interval of possible resistances of the resistor R1 in kiloohms when using microcircuits of the series indicated in brackets is 0.1 ... 1.8 (K155). 0.1...5.6 (K555). 0.15...30 (KR1533) or 0.15...91 (K561). When the resistance approaches one of the boundary values, the complete breakdown of the oscillations is often preceded by a "bounce" - the generation of bursts of short pulses at the fronts of the main ones. In the generator according to the scheme of Fig. 4, only microcircuits of the CMOS structure (K561 series and the like) can work, and the resistance R1 must be in the range of 0.8 ... 300 kOhm.

On fig. 5 shows a diagram of an economical burst generator containing only one logic element - a Schmitt trigger. During the flash of the "flashing" LED HL1, the voltage level at input 1 of the DD1.1 element corresponds to logic 0. In the pause between flashes, this voltage increases to the level of logic 1 and the RC generator starts to work. formed by the elements R2, C1, DD1.1. At the output, you can observe bursts of pulses following with the frequency of LED flashes. The signal can be heard by connecting a BF1 acoustic transducer to the output of the generator, for example, a piezo emitter ZP - 1, ZP - 19 or ZP - 22. The values \u200b\u200bof the elements indicated in the diagram correspond to a pulse frequency in a pack of 2 kHz. the repetition period of the bursts is 500. and the duration of each of them is 230 ms. With an increase in the resistance of the resistor R1 from 620 Ohm to 150 kOhm, the burst repetition period increases from 450 to 600 ms, and their filling frequency decreases from 2.2 to 1.5 kHz. You can pick up such a resistance (approximately 135 kOhm). at which a sequential melodic triad is generated. By swapping R1 and HL1, by selecting the same resistor, they achieve such an interesting effect as "glissando" - a smooth change in pitch.

It should be borne in mind that for all the generators considered here, with large values of the load resistor, the brightness of the light pulses decreases so much that they become invisible. However, the generation of electrical impulses continues.

Perfection is not achieved when there is nothing to add,
and when there is nothing to remove.
Antoine de Saint-Exupery

Many radio amateurs, of course, have come across SMT (Surface mount technology) printed circuit board surface mount technology, met SMD (Surface mount device) elements mounted on the surface and heard about the advantages of surface mounting, which is rightfully called the fourth revolution in electronic technology after the invention lamp, transistor and integrated circuit.

Some find surface mounting difficult to implement at home due to the small size of the SMD elements and ... the lack of holes for the leads of the parts.
This is partly true, but upon closer examination, it turns out that the small dimensions of the elements simply require accuracy during installation, of course, provided that we are talking about simple SMD components that do not require special equipment for installation. The absence of reference points, which are holes for the leads of parts, only create the illusion of difficulty in making a printed circuit board drawing.

You need practice in creating simple designs on SMD elements in order to gain skills, self-confidence, and make sure that surface mount is promising for yourself. After all, the process of manufacturing a printed circuit board is simplified (no need to drill holes, form the leads of parts), and the resulting gain in mounting density is noticeable to the naked eye.

The basis of our designs is an asymmetric multivibrator circuit based on transistors of various structures.

We will assemble a flasher on an LED, which will serve as a talisman, and also create a reserve for future designs by making a prototype of a chip popular with radio amateurs, but not quite accessible.

Asymmetric multivibrator on transistors of different structures

(Fig. 1) is a real "bestseller" in amateur radio literature.

Rice. 1. Scheme of an asymmetric multivibrator

By connecting certain external circuits to the circuit, you can assemble more than a dozen structures. For example, a sound probe, a Morse code generator, a mosquito repellent, the basis of a monophonic musical instrument. And the use of external sensors or control devices in the base circuit of the VT1 transistor allows you to get a watchdog, an indicator of humidity, light, temperature, and many other designs.

--
Thank you for your attention!
Igor Kotov, editor-in-chief of Datagor magazine

List of sources

1. Mosyagin V.V. Secrets of amateur radio skill. – M.: SOLON-Press. – 2005, 216 p. (pp. 47 - 64).
2. Shustov M.A. Practical circuitry. 450 useful schemes for radio amateurs. Book 1. - M .: Alteks-A, 2001. - 352 p.
3. Shustov M.A. Practical circuitry. Control and protection of power supplies. Book 4. - M .: Alteks-A, 2002. - 176 p.
4. Low-voltage flasher. (Abroad) // Radio, 1998, No. 6, p. 64.
5.
6.
7.
8. Shoemaker C. Amateur control and signaling circuits on the IS. - M: Mir, 1989 (scheme 46. Simple battery discharge indicator, p. 104; scheme 47. Drawer marker (flashing), p. 105).
9. Generator on LM3909 // Radio scheme, 2008, No. 2. Diploma specialty - radio engineer, Ph.D.

The author of the books “To a young radio amateur for reading with a soldering iron”, “Secrets of amateur radio skill”, co-author of a series of books “For reading with a soldering iron” in the publishing house “SOLON-Press”, I have publications in the journals “Radio”, “Instruments and Experimental Techniques”, etc. .

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Pulse generators with flashing LED

So-called "Blinking LED Lamps" appeared in the catalogs of foreign firms manufacturing and selling semiconductor devices - light-emitting diodes that look ordinary, but when connected to a constant voltage source, flash and go out about twice a second. These devices can often be purchased at radio markets. This article describes several simple devices in which a "flashing" LED serves as a generator of not only light, but also electrical impulses.

First of all, let's answer the question, why does such an LED blink? Inside it, as shown in the diagram (Fig. 1), in addition to the actual light-emitting semiconductor structure HL1, there are a pulse generator and an electronic key. Sometimes a quenching resistor R1 is provided, in other cases, its functions are performed by the internal resistance of the key. Diode VD1 protects the device from supply voltage of reverse polarity.

To open the world of radio electronics full of mysteries without having a specialized education, it is recommended to start with the assembly of simple electronic circuits. The level of satisfaction will be higher if the positive result is accompanied by a pleasant visual effect. The ideal option is circuits with one or two blinking LEDs in the load. Below is information that will help in the implementation of the most simple do-it-yourself schemes.

Ready flashing LEDs and circuits using them

Among the variety of ready-made flashing LEDs, products in a 5 mm case are the most common. In addition to ready-made single-color flashing LEDs, there are two-pin instances with two or three crystals of different colors. They have a built-in generator in the same case with crystals, which operates at a certain frequency. It gives out single alternating pulses to each crystal according to a given program. The blinking speed (frequency) depends on the set program. When two crystals are lit at the same time, the blinking LED produces an intermediate color. The second most popular are flashing light emitting diodes controlled by current (potential level). That is, to make an LED of this type blink, you need to change the power at the corresponding pins. For example, the color of the emission of a two-color red-green LED with two leads depends on the direction of current flow.

The three-color (RGB) flashing LED with four pins has a common anode (cathode) and three pins for controlling each color separately. The flashing effect is achieved by connecting to an appropriate control system.

Making a flasher based on a ready-made flashing LED is quite easy. This will require a CR2032 or CR2025 battery and a 150-240 ohm resistor, which should be soldered to either pin. Observing the polarity of the LED, the contacts are connected to the battery. The LED flasher is ready, you can enjoy the visual effect. If you use a krone battery, based on Ohm's law, you should choose a resistor of greater resistance.

Ordinary LEDs and flashing lights based on them

A novice radio amateur can assemble a flasher on a simple single-color light-emitting diode, having a minimal set of radio elements. To do this, consider several practical schemes that differ in the minimum set of radio components used, simplicity, durability and reliability.

The first circuit consists of a low-power transistor Q1 (KT315, KT3102 or a similar imported analogue), a 16V polar capacitor C1 with a capacity of 470 uF, a 820-1000 Ohm resistor R1 and an L1 LED like AL307. The entire circuit is powered by a 12V voltage source.

The above circuit works on the principle of avalanche breakdown, so the base of the transistor remains “hanging in the air”, and a positive potential is applied to the emitter. When turned on, the capacitor is charged, up to about 10V, after which the transistor opens for a moment with the return of the accumulated energy to the load, which manifests itself in the form of a blinking LED. The disadvantage of the circuit is the need for a 12V voltage source.

The second circuit is assembled on the principle of a transistor multivibrator and is considered more reliable. To implement it, you will need:

two transistors KT3102 (or their equivalent);
two polar capacitors for 16V with a capacity of 10 microfarads;
two resistors (R1 and R4) of 300 ohms to limit the load current;
two resistors (R2 and R3) of 27 kΩ each to set the base current of the transistor;
two LEDs of any color.

In this case, a constant voltage of 5V is applied to the elements. The circuit works on the principle of alternate charge-discharge of capacitors C1 and C2, which leads to the opening of the corresponding transistor. While VT1 dumps the accumulated energy C1 through an open collector-emitter junction, the first LED is lit. At this time, a smooth charge of C2 occurs, which helps to reduce the base current VT1. At a certain moment, VT1 closes, and VT2 opens and the second LED lights up.

The second scheme has several advantages at once:

It can operate in a wide voltage range starting from 3V. When applying more than 5V to the input, you will have to recalculate the resistor values so as not to break through the LED and not exceed the maximum current of the transistor base.
2-3 LEDs can be connected to the load in parallel or in series by recalculating the resistor values.
An equal increase in the capacitance of the capacitors leads to an increase in the duration of the glow.
By changing the capacitance of one capacitor, we get an asymmetric multivibrator, in which the glow time will be different.

In both cases, it is possible to use pnp conduction transistors, but with correction of the wiring diagram.

Sometimes, instead of blinking LEDs, a radio amateur observes a normal glow, that is, both transistors are partially open. In this case, you need to either replace the transistors, or solder resistors R2 and R3 with a lower rating, thereby increasing the base current.

Keep in mind that 3V power will not be enough to light an LED with a high forward voltage value. For example, a white, blue, or green LED will require more voltage.

In addition to the considered circuit diagrams, there are a great many other simple solutions that cause the LED to flash. Novice radio amateurs should pay attention to the inexpensive and widespread NE555 chip, which can also implement this effect. Its versatility will help to collect other interesting schemes.

Application area

Flashing LEDs with a built-in generator have found application in the construction of New Year's garlands. By assembling them in a series circuit and installing resistors with a slight difference in value, they achieve a shift in the blinking of each individual element of the circuit. The result is a beautiful lighting effect that does not require a complex control unit. It is enough just to connect the garland through the diode bridge.

Current-controlled flashing light-emitting diodes are used as indicators in electronic engineering, when each color corresponds to a certain state (on / off charge level, etc.). Also, electronic displays, advertising signs, children's toys and other goods are collected from them, in which multi-colored flashing is of interest to people.

The ability to assemble simple flashing lights will be an incentive to build circuits on more powerful transistors. With a little effort, you can create many interesting effects with the help of flashing LEDs, for example, a traveling wave.

Read also

Having supplemented the previous generator with several details, it will be possible to obtain an LED “flasher” (Fig. 2.3).

The generator works as follows. When the power supply is turned on, capacitors C1 and C2 begin to charge.

Rice. 2.2. Printed circuit board and placement of sound probe elements

Rice. 2.3. Transistor Light Pulse Generator

each in his own chain. Capacitor C1 in the circuit R1, C1, R2, and capacitor C2 in the circuit R3, C2, R2. Since the time constant of the second circuit is much less than the first, capacitor C2 will first charge to the power supply voltage. As the capacitor C1 charges, the transistor VT1 starts to open and opens the transistor VT2. Further, the process of tearing off both transistors occurs like an avalanche. The resistance of the emitter-collector section of the transistor VT2 becomes very small, and the supply voltage of the battery GB1 is applied to the resistor R2. Thanks to the elements R3, C2, called the “voltage boost” circuit, the capacitor C2, charged to the power supply voltage, is connected in series with the galvanic cell and the voltage applied to the LED almost doubles. In the process of discharging capacitor C2, the LED glows for some time, since a voltage above the threshold is applied to it. Capacitor C1 also begins to discharge, which leads to the closing of the transistor VT1, followed by VT2. This process again occurs like an avalanche, until both transistors are reliably closed. Next, the capacitors C1 and C2 begin to charge again and the operation of the device is repeated, as described above.

The generation frequency depends on the resistance of the resistors R1, R2, the capacitance of the capacitor C1 and the voltage of the power supply GB1. With the values of the indicated elements indicated on the diagram, it is about 1.3 Hz. The current consumed by the device from the battery is 0.12 mA. When powered by an AA cell, this device is like a “Pink Floydich light bulb” (Pink Floyd once released a CD with the Pulse album, in which a flashing LED was built in) - capable of continuously working for more than one year.

The light emitting diode HL1 must have an operating voltage of less than 2 V. You can use AL112, AL307A, AL310, AL316 (red glow), AL360 (green glow).

The printed circuit board and the placement of elements of the light pulse generator on transistors are shown in fig. 2.4. You can use transistors KT315, KT361 with any letter indices. Capacitor C1 type K10-17, K10-47, oxide C2 - K50-16, K50-35. In simple designs like this, printed circuit wiring can be omitted by making it with a pre-tinned copper wire 0.4 ... 0.6 mm thick. The leads of the parts are cut off at a distance of 3 ... 4 mm from the board and 1-2 turns of the mounting wire are made around each lead. Then the coils are soldered with a soldering iron. On the conclusions of the elements that are raised above the board (transistors VT1, VT2, LED HL1), put on pieces of polyvinyl chloride tubes, preferably multi-colored. You can enter your own “standard” for marking elements, for example, always use blue tubes to output the emitter, red tubes for the collector, and white tubes for the base. By the way, during installation, place the elements on the board so that the inscriptions on them can always be read. Even better, all the inscriptions should be facing the same direction, for example, from left to right.

Another generator of light pulses is a shaper of rectangular pulses on the OS (Fig. 2.5). Resistors R1, R2 form an artificial midpoint. The negative feedback circuit is formed by elements R5, C1, and the positive feedback circuit is formed by the divider R3, R4. The output voltage of the generator is supplied to a non-inverted

%is. 2.4. Printed circuit board and placement of elements of the light pulse generator

Rice. 2.5. Op-amp light pulse generator

^exmax r ^n, A =

tying input through the divider R3, R4 with a division factor K = -. Suppose that the output of the op-amp has -

This is the maximum voltage (with respect to the artificial midpoint of the connection of resistors R1, R2), which we denote + Ubwx max - From this moment in time, the capacitor C1 begins to charge through the resistor R5. The op-amp operates in the comparator mode (comparison device), compares the voltage across the capacitor C1 with part of the output voltage DZ

main entrance. Until the time when the voltage at the inverting input is less than at the non-inverting one, the output voltage of the op-amp does not change. As soon as the switching threshold of the op-amp is exceeded, the output voltage begins to decrease, and the positive feedback through the divider R3, R4 gives this process an avalanche-like character. The voltage at the output of the op-amp quickly reaches its maximum negative value -Pout max- The process of recharging capacitor C1 will go the other way. As soon as the voltage across the capacitor C1 becomes more negative than the voltage across the resistor R3 of the divider R3, R4, the op-amp again

Rice. 2.6. Printed circuit board of the generator of light pulses on the OS with the placement of elements

will go into a state in which the output voltage becomes positive + Ubwx max- Then the process will be repeated. Thus, when generating oscillations, the capacitor C1 is periodically recharged in the voltage range from +Ubwx maxK TO -Pout maxK. The oscillation period of the multivibrator is T = = 2D5S11p. At R3-= R4, the oscillation period is T = 2.2R5 C1.

The printed circuit board and placement of elements are shown in fig. 2.6. In addition to the K553UD2 op-amp, you can use K153UD2, as well as many other op-amps, for example, KR140UD608, KR140UD708. The place of installation of these types of OS is shown in fig. 2.6 dashed lines. Since these op-amps have internal frequency correction circuits, there is no need for capacitor C2 in this case. Resistors MLT, S1-4, S2-10, S2-33 with a power of 0.125 or 0.25 W, capacitors KM, KLS, K10.

Considering that almost any type of op-amp works in the light pulse generator, it is possible to make a kind of “tester” for checking the op-amp. An interesting design of such a device is proposed in.

The third circuit of the light pulse generator is based on a digital CMOS microchip. It can be used as a simulator of a security system, in toys, in signaling schemes for operating modes. The scheme of the light pulse generator is shown in fig. 2.7. It consists of a generator on the elements DD1.1, DDI.2 and buffer elements connected in series DD1.3, DDI.4. Due to the low load

the ability of the CMOS elements in the generator, power amplifiers are installed on transistors VT1, VT2 and VT3, VT4. At the outputs of power amplifiers, pulses of opposite polarity are observed with a repetition rate determined by the frequency-setting elements R2, C1 of the generator. The oscillator frequency is approximately equal to Fr= 1.4 R2C1. With the elements indicated in the diagram, it is about 1 Hz.

Capacitor C2 is a blocking capacitor in the power supply circuit of the device. Resistor R1 protects the input of the microcircuit from overloads, resistors R3, R4 determine the current through the LEDs. As an example, in fig. 2.7 shows four options for connecting light diodes to a light pulse generator, which can be used in specific designs of a radio amateur. To improve the understanding of the principle of operation of the device, capacitors C3, C4 are shown where they are used in operation.

For the first and second options, it is not required to install transistors VT2, VT4 and capacitors C3, C4. In the first option, separate LEDs of any glow color are used, connected by the anode to outputs 1 and 2 of the generator (or only to one of the outputs). The most widely used LEDs of the AL307 series have the following glow colors depending on the indices: K - red, R - orange, M, E - yellow, G - green.

In the second version, a two-color ALS331AM LED with separate leads from the crystals is used, which alternately lights up in green and red.

The third and fourth connection options are designed for the use of two-color LEDs with back-to-back connection. Here you can use KIPD41A-KIPD41M LEDs or any of the KIPD45 series.

In the third option, capacitors C3, C4 are not installed, resistor R4 can be replaced with a jumper, and resistor R3 has a rating of 470 ohms.

In the fourth connection option, the resistance of resistors R3 and R4 is about 120 ohms. By selecting the resistances of these resistors and selecting the capacitances of the capacitors C3, C4, you can set different flash durations for the LEDs HL5, HL6. With an increase in capacity, the color of the glow will change abruptly; when indicated in the diagram, short flashes are observed with an alternate change in the color of the glow.

The printed circuit board of the light pulse generator and the placement of parts on it are shown in fig. 2.8. In the generator, in addition to that indicated in the diagram, you can use a similar chip of the K1561 series. When changing the pattern of the printed circuit board, other microcircuits of the K176, K561, K1561 series can also be used. Capacitor C1 type K10-17, K73, K78, the rest [e - K50-6, K50-16, K50-35. Resistors MLT, S2-33, S1-4. Transistors VT1, VT3 - any of the KT315, KT3102 series, and VT2, VT4 - from the KT361, KT3107 series.

Rice. 2.8. Printed circuit board and placement of elements of the light pulse generator on a digital microcircuit

Establishing a light pulse generator comes down to setting the required switching frequency of the LEDs, which can be roughly selected by selecting the capacitor C1, or rather, the resistor R2. At the time of frequency tuning, R2 can be made up of two resistors - variable (1 ... 2 mOhm) and constant 100 kOhm. After setting the required frequency of the generator, the resistance of the chain of the indicated resistors is measured and replaced with a constant. Sometimes it is required to change the brightness of the LEDs, which is selected by selecting resistors R3, R4. Care must be taken not to exceed the maximum current through the LEDs.