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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING LED garland. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting The proposed LED garland is extremely simple (its diagram is shown in Fig. 1, a) and is designed to be installed on a small desktop artificial Christmas tree or on spruce branches placed in a vase of water. The peculiarity of the garland is in its manufacturing technology: in order to reduce the risk of mechanical destruction of the LEDs under the action of a tensile force created by the connecting wires soldered to their relatively long terminals, the terminals in this garland are shortened to 3 mm before installation. And in order not to damage the LED when soldering at such a close distance from the crystal, solder with a low melting point (96 оC) - Rose's alloy, containing, in addition to tin and lead (25% each), also bismuth (the rest).
I recommend cutting the LED leads for the garland not with wire cutters, but with scissors so that sharp edges do not form, and after soldering three layers of nail polish, it was enough for safe electrical insulation. To connect the LEDs to each other and to the mains plug, use an MGTF wire with a cross section (for copper) of 0,1 or 0,12 mm2 in fluoroplastic insulation (preferable because its insulation does not deform when heated). The ends of the wires soldered to the LEDs are pre-tinned with ordinary tin-lead solder. This is necessary so that when soldering them to the LEDs with Rose alloy, the twisted ends of the wires do not unwind with the formation of sharp protrusions (which will then be difficult to isolate well with varnish), but remain round. When tinning wires, it is better to use not rosin (it will not melt when soldering with Rose alloy), but the so-called soldering acid, which is a solution of zinc chloride, that is, a product of the chemical reaction of zinc with hydrochloric acid. The wires that make up the core of the wire must be twisted before tinning, and in order for the twist to remain round, do not put pressure on it during tinning. Before soldering the wires, the cut leads of the LEDs should be carefully cleaned with a sharp razor from all sides, and then tinned with a Rose alloy with soldering acid, otherwise the soldering will be fragile and the wires may then come off. After completing the installation, all soldering points and adjacent areas of wires and LED leads free from insulation must be covered with at least three layers of nail polish. In the author's garland, the LEDs are connected to each other by pieces of wire about 150 mm long, from the extreme LEDs to the mains plug - about 1,7 m. At a distance of about 150 mm from the plug on the wires there is a plastic box measuring 65x40x20 mm, in which there is a VD1 diode and a resistor R1 (MLT-2). Two holes for M3 screws are drilled in one of its walls for fastening the wires. Inside the box, each end of the wire, in which the diode and resistor are connected, is made one turn around its screw, after which the wires are firmly clamped between the wall of the box and cardboard washers, over which metal washers are put on the screws and nuts are screwed on. The diode and resistor hang on wires, they are reliably isolated from screws and nuts with insulating tubes and varnish. Instead of D226, you can use any silicon diode with a forward current of at least 50 mA and a reverse voltage of at least 400 V (for example, KD209A-KD209V, 1N4004-1N4007, etc.). To work with low-melting solder, a conventional 30watt electric soldering iron connected to the network through a power regulator. The device (its diagram is shown in Fig. 2) is based on the regulator described in the article by Ivanov B. "Where to start. Soldering iron stand" ("Radio", 1997, No. 9, p. 33). Unlike the original, it uses a more powerful trinistor VS1, a switch (SA1) for power control limits is introduced, a diode VD1 is added (to protect the control electrode of the trinistor from reverse voltage) and an LED HL1, which indicates that a load is connected to the device that consumes a small (but not less than 0,4 W) power, and also introduced an LC filter L1C1, which prevents interference from entering the power grid that occurs when the trinistor is turned off.
The device is mounted on a fiberglass board 60x65 mm in size, placed in a plastic case 100x70x40 mm in size. Possible replacement of trinistor KU202N (VS1) - KU202M, diodes D229B (VD1, VD2) - D226, D237B. Switch SA1 - toggle switch TV-1. Variable resistor R3 - SP-1, capacitor c2 - oxide K50-12, C1 - MBM with a rated voltage of 750 V or imported film, designed to operate at an alternating voltage of at least 250 V. Choke L1 contains 150 turns of winding wire of any type with a diameter of 0,2 ,0,3 ... 400 mm, wound in two layers on a ferrite (700НН, 8НМ) core magnetic core with a diameter of 38 and a length of XNUMX mm, interlayer insulation - PVC electrical tape. On the control knob of the variable resistor R3, a radial mark is made indicating its position relative to the scale. The latter is located on the body of the device and consists of 50 strokes with a step of approximately 1 mm. Every fifth stroke is elongated, every tenth is digitized (which corresponds to 0, 10, 20, 30, 40 and 50 conventional power units). This conditional scale is intended only for orientation (it allows you to fix and remember the position of the handle corresponding to different temperatures of the soldering iron - working with Rose alloy, with other solders, etc.). In the "100%" switch position, it is convenient to perceive the scale as a continuation of the scale of the previous interval: for example, setting the knob to 10 is like 50 + 10 = 60, to 20 is like 50 + 20 = 70, etc. The power regulator can also be useful when using a soldering iron to work with polymer hot melt adhesive in the form of rods (without a regulator, hot melt adhesive burns on the soldering iron tip). You can adjust the regulator (find out which scale mark to set the knob of the variable resistor R3 when soldering with Rose alloy, other solders or when working with hot melt adhesive) by measuring the temperature of the soldering iron tip with a thermocouple from the DT838 digital multimeter kit. The surface temperature of the tip near the stripped tip for soldering with Rose alloy should be (8 minutes after plugging in) within 150 ... 160 оC (this is approximately 17,5 divisions). If there is nothing to measure the temperature with, then, having determined the scale mark when the Rose alloy begins to melt, add three or four more divisions to this (so that the solder does not clump and is liquid enough), this will be the position of the handle corresponding to work with Rose alloy. Author: E. Pankov
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