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9v low battery indicator circuit11/24/2023 ![]() It's possible that many of the components you'll use in the beginning won't be so sensitive to this, like resistors or capacitors. Touching the LED when you're statically charged to a few kilovolt will also kill the LED. LEDs are sensitive to ESD, ElectroStatic Discharge. There's still another possible explanation why it doesn't work. Note that, due to the high input voltage, the power dissipated will be a bit more than 300mW, so a 1/4W resistor won't do. The closest value you'll find will probably be 820\$\Omega\$. Then you use Ohm's Law to calculate the series resistor: The same datasheet says 40mcd at 20mA, and the voltage is 2V typical. You want to know the LED's nominal current, which is often around 20mA for an indicator LED, but also its voltage drop. Nine out of ten it's too high, though you should still see the LED light faintly. One LED will be correctly polarized and that will light, the other one will be reverse polarized, but the first one's forward voltage (around 2V for a red LED, 3.5V for a white one) will limit the reverse voltage to a safe level.Īnother thing mentioned is your resistor. Place a resistor in series and connect to a 9V battery (or your new power supply!). Place two of your LEDs in anti-parallel: the anode of one LED to the other's cathode, and vice versa. If you wouldn't have a datasheet there's still a safe way to try it. That's your anode, which goes to the plus. Use whatever the manufacturer indicates as the anode. Usually! Don't try it if you're not sure, remember you don't get a second chance. One pin is longer than the other, the LED's rim isn't complete on one side, and if you look into the LED you may see a thin wire going from the chip to one of the pins. ![]() ![]() There are a few differences between the pins. Here's the drawing from the datasheet for a random LED: No design engineer would use a part if he can't get the datasheet for it. Try to make it a habit to use components you've got information on. What did you do? Just try it one way and reverse it if you saw it was wrong? OK, now you know that you can't afford this with LEDs. You'll need one for everything you want to do.ĪndrejaKo and the others already told you what's probably wrong: you installed it the wrong way, which killed it, because while most diodes can stand the 18V reverse, LEDs can't. Since you're new to electronics the power supply is a good way to start.
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