Garland on the blinking light-emitting diodes. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Among the variety of flashing Christmas tree garlands, "simple ultra-modern" ones, consisting ... only of LEDs, are becoming increasingly popular. Instead of the usual pile of circuit solutions (with electronic keys that are periodically opened and closed by low-frequency RC-, RL- or LC generators), there are small-sized semiconductor light emitters. True, the LEDs, acting as a kind of microswitches, are not simple (Fig. 1a-1c). The name of this class of optoelectronic devices, developed at the intersection of integrated microelectronics and optics, is Blinking LED lamps (blinking LEDs, or MSVs).

The flashing LED is based on a frameless CMOS generator A1 (Fig. 1c). It is he who periodically opens and closes the electronic key A2. The HL1 LED located here, respectively, flashes at a frequency of 1,5-2,5 Hz. Moreover, the design itself is such that the MCB can be connected (thanks to the built-in resistor R2) to a direct voltage source directly, without an external current limiter.

Strictly speaking, in this semiconductor optoelectronic device there is also a low-resistance resistor R1 with a value of 5-8 Ohms, but it can be ignored when considering the general principle of operation. Typical characteristics of the MCB are such that when the supply changes from 3,5 to 13 V, the forward current is in the range from 6 to 60 mA.

Diode VD1 performs a protective function (in case of reverse voltage). Well, a long flow of a large current through it (150-200 mA) threatens to disable the MCB.

As can be seen from the generalized functional diagram of a blinking LED, it has its own frequency-setting capacitor C1, like the previous devices with electronic keys. Only it has a low capacity, since it is implemented as a distributed integrated structure on a common substrate. The low generation frequency (2 Hz) is primarily due to internal ultra-high-resistance CMOS resistors. The inevitable technological spread in production leads to the fact that it is very rare to meet two absolutely identical (in terms of generation frequency) MSWs.

Flashing LEDs (Fig. 1a) outwardly differ little from typical AL307, well known to many radio amateurs. Even with the naked eye, in each of the optoelectronic "newcomers" one can see a "chip" (in this case, it is a substrate with integrated elements), a monolithic light guide made of super-dispersive plastic, as well as a cathode and an anode.

On circuit diagrams, MCBs are depicted in the same way as conventional LEDs. The only graphical difference is that instead of a pair of solid "light emitter" arrows, two dotted ones are drawn.

Rice. 1. Flashing LED (a), its symbol (b) and generalized functional diagram (c): 1 - anode; 2 - cathode; 3 - substrate (semiconductor, with integrated elements); 4 - monolithic light guide (made of super-diffusing plastic).

Rice. 2. New Year's souvenir with flashing LEDs (a) and its circuit diagram (b)

HL1, HL8, HL15 L-56 BHD (L-56 BGD, L-56 BYD)

НL2-НL7, НL9-НL14, НL16-НL21 AL307BM (AL307GM)

Х2.ХЗ Dendy - connectors (СГ5, СШ 5)

Rice. Fig. 3. The recommended variant of connecting LEDs in the form of a stylized Christmas tree (a) and its modification using the example of one of the sections of a flashing electronic garland (b)

Next to the blinking LED icon are the letters HL with the corresponding serial (according to the scheme) number, as well as a code name, based on which you can determine the color of the radiation and other characteristics of this MSV. Among the most common are relatively inexpensive L-56BHD (red), L-56BGD (green), L-56BYD (yellow) from King-bright or their analogues. The outer diameter of these devices is about 5 mm, which allows MCBs to be successfully placed on panels with conventional LEDs of the types AL307BM and KIPD40A1 - K (red), AL307GM and KIPD40A1-L (green), AL307ZhM and KIPD40A1-Zh (yellow).

Now, after a brief acquaintance with a new class of available optoelectronic devices, it is proposed to make an original New Year's souvenir using flashing and ordinary LEDs (Fig. 2a). In fact, this is a garland shimmering with multi-colored lights (Fig. 2b) of three light-emitting sections of seven semiconductor devices each, which is made in the form of a stylized Christmas tree.

A ready-made power supply is suitable as a source of energy. For example, from the DENDY game console or the more powerful SEGA MEGA DRIVE-2. But a self-made device (with a constant voltage of 14-16 V and a current of 0,1-0,2 A at the output) is also quite acceptable, made in the form of an adapter plug and including a step-down transformer T1, a rectifier bridge VD1 -VD4, a filter capacitor C1, input X1 and output X2 electrical connectors.

When power is applied, the LED chains start flashing at a short interval (about 2 times per second). Each of the three MSVs has its own flare frequency, slightly different from the indicated one; therefore, the garland shimmers with lights, forming a variety of combinations of light geometric shapes. In addition to everything, the absence of hard synchronization between the CMOS generators, which, as emphasized above, are part of the flashing LEDs, also affects here. There is an element of chance in the operation of the scheme, and the resulting illumination does not bother the audience.

The design of the Christmas tree base itself can be different, depending on the tastes and experience of the manufacturer. For example, in the standard version for mounting, a front textolite panel 200x150x0,5 mm is used with 3 mm holes drilled in it according to the plan (Fig. 5a) for 21 LEDs. The case of each of the future New Year's lights is inserted and glued to such a board with a compound or a quick-drying "Moment", and the electrical connection of the elements of the garland into a single whole is carried out with a wire of the MGPV-0,2 type using a small-sized soldering iron, rosin and low-melting solder (the soldering time of the leads should not exceed 1-2 s). The rear and side walls of the Christmas tree base can be made of one-sided foil fiberglass, fastened along the ribs by soldering.

To make an equally attractive version of a New Year's souvenir, they take foam rubber 200x150 mm in size and 10-20 mm thick, into which LEDs are stuck so that a Christmas tree pattern is formed from them. The conclusions of each of these semiconductor devices on the back of the foam rubber are carefully unbent and connected with thin wires according to the wiring diagram (Fig. XNUMXa).

As practice shows, the establishment of a homemade product, assembled in strict accordance with the electrical circuit diagram from known good radio components, does not cause difficulties even for inexperienced beginners.

The most common mistake is the wrong polarity of turning on one or more LEDs. For safety, it is recommended to solder into the structure (before the first test of the Christmas tree-garland) a current-limiting resistor R1, highlighted in the circuit diagram (Fig. 2b) by a dotted line. Then the souvenir is included in the network. By measuring the voltage drop across R1 with a voltmeter (preferably digital), they are convinced that, although the controlled value is constantly changing, the readings of the device, even with the simultaneous flash of all LEDs, do not exceed 3 V. Otherwise, you need to look for errors in the installation.

If it suddenly turns out: the circuit is assembled flawlessly, and for some reason the controlled value is less than 1,5 V, then they go to replace the resistor indicated above with a simple jumper. The optimal option can be considered in which the current limiter remains in the circuit. In this case, the value of R1 is selected so that the ratio of U in volts to R1 in ohms does not exceed 0,06 (that is, the maximum current flowing through the limiting resistor was not more than 60 mA).

Fans of experiments, of course, have the right to arrange semiconductor light emitters in their own way in order to achieve the most expressive lighting effects from an already debugged circuit. It is important to observe the rules of symmetry, including the color and types of LEDs for each of the daisy chains. And if the power reserve of the power supply allows, then, apparently, it makes sense to increase the number of New Year's lights in a souvenir to 27 pieces, using, for example, a modification (Fig. 3b) of the electrical circuit diagram of the device.

The reliability of such a technical solution is guaranteed if the maximum current through the resistor R1 when debugging the garland does not exceed 120 mA.

Author: S.Ryumik

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