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Easy to manufacture and functional in use tester made by the author homemade.
For the tester you need: a syringe for five cubes, a wire with a clamp, two LEDs (different emission spectrum), 4 batteries, a steel wire.
The tester circuit is as follows.
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First, the author of the homemade solder on the other hand two LEDs, i.e. solder the small leg of one to the large leg of the other.
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A resistor is soldered to one of the legs of the LED, a piece of steel wire is connected to the resistor.
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The place of soldering, LEDs, the resistor fills with hot glue. Bends the second end of the LED to form a battery contact. Fills a few drops of hot-melt adhesive into the syringe and inserts the soldered block into it, the wire sticks into the hole of the syringe. A hole is made in the piston of the syringe and, having inserted the end of the wire there (with a clip), it bends to form the second contact of the batteries. Inserts batteries into the syringe, inserts a piston with contact on top.
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A piece of tube from a dropper is put on a piece of wire. This tester has two functions. With it, you can check the voltage of 12 V or short circuit, and the indication will shine with a different light.
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