Christmas garlands with flashing LEDs. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur
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In the presence of flashing LEDs, you can assemble garlands from ordinary LEDs and small-sized incandescent lamps that will flash randomly.
The first device (Fig. 5) consists of ten groups, in each of which the garland is made of sequentially connected flashing LEDs (EL1, EL11, EL21, etc.) and ordinary ones. Therefore, when the garlands are connected to a power source, the LEDs will flash and go out simultaneously with their blinking LED. This happens because when you turn on, for example, the EL1 LED, a current of about 10 mA will flow through it and the rest of the LEDs of the group - it is determined by the supply voltage, the number of LEDs in the group and the resistance of the resistor R1. All LEDs in the group will be lit.
When the flashing LED turns off, the rest of the LEDs will turn off. And this will happen in every group.
In the manufacture of this garland, it is better to use flashing LEDs of different colors of glow and different types, so that the frequency of flashing of each group in the garland is different. Then the effect of pseudo-chaoticity will be created. The number of conventional LEDs must be defined - depending on their type and supply voltage. For example, at 12 V, the number of LEDs can be from 9 to 12. To more accurately determine the maximum allowable number of LEDs, you should measure the operating voltage of each LED used. And for this you will have to assemble a kind of probe (Fig. 6). By connecting the EL1 LED to it, the current is set to 1 mA with a variable resistor R10 in the circuit and the voltage drop across the LED is measured.
Having thus measured the luminous voltage of the LEDs of all applied series and colors (one from each series), it is possible to determine the number of LEDs in each group. The total voltage of the LEDs should be approximately 5 V (flashing LED voltage) less than the supply voltage. Finally, the current through the LEDs of each group is set within 9 ... 12mA by selecting the appropriate limiting resistor (R1 - R10). It should be noted that the difference between the supply voltage and the voltage drop across all ordinary LEDs of the group must not exceed the maximum allowable voltage of the blinking LED (usually 9...12 V).
As flashing LEDs, you can use V621-V623, L-36BHD, L-56, L-616, L-796, L-819, etc. The rest of the LEDs are any domestic or imported, with different glow colors, but preferably the brightest.
The following design (Fig. 7) also uses the properties of flashing LEDs, but they control groups of garlands made up of small incandescent lamps. For example, five groups are shown, although there may be more or less.
Consider the principle of operation of one of the groups, say, the top one according to the scheme. When the blinking LED HL1 is working, rectangular pulses are formed on its anode. Through the resistor R2 and trimmer R3, they enter the base of a powerful composite transistor VT1. When the LED flashes, the transistor opens, the lamps EL1 - EL10 connected in series are lit. When the LED goes out, the transistor closes, the lamps go out. The rest of the groups work similarly.
As in the previous design, the LEDs can be of different colors from the types indicated. Power supply - any, designed for the specified voltage and total current through the lamp chains. With the specified supply voltage, it is permissible to use lamps for a voltage of 2,5 V and a current of 0,15 - 0,25 A in each chain. LEDs can be placed on the front panel of the case for a visual demonstration of the operation of the switch. Transistors - any of the series indicated on the diagram.
Establishing the machine comes down to setting clear thresholds for opening and closing transistors with appropriate tuning resistors.
Author: I.Potachin, Fokino, Bryansk region
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