Hi,, Im new to this forum and electronics. i have a problem too... I connected two led bulbs (green and red) through usb cable to computer. but first led is only worked. 2nd one is not worked... 5v coming from the usb cable... y s that happend???
That doesn't always help, especially if the LEDs are used or have trimmed leads. In most cases, the side with the flat edge is the cathode (negative), but if you really can't tell, look inside the LED. The side connected to what looks like a bowl is the cathode. Unless you want to discuss multicolor LEDs, then it's a whole different matter.The longer wire is the positive electrode and the shorter wire is the negative electrode.
Hi,, I'm new to this forum and electronics. I have a problem too... I connected two led bulbs (green and red); through usb cable to computer. But first led is only worked. 2nd one is not worked... 5v coming from the usb cable... y s that happened???
Yes, this sometimes happens. I have a few 3mm LEDs that have the flat edge on the side (not above either of the pins), so I try to look at where the "bowl" is. You can test with a couple of volts though, and on some meters your diode test function will work as well. It will also tell you the forward voltage drop of the LED.Some of my LEDs don't have a flat, so I check polarity with 2-3 volts.
Excellent point. Assuming you're getting exactly 5v from your USB port and your LED has a voltage drop of 3v, and an operating current of 25mA, you'll need a resistor with a value of (5-3)/0.025 = 80 ohms. I'd just choose 100 ohms to be safe. You definitely may have blown the LED if you didn't limit the current with a resistor.5 Volts from the USB, may have blown one of the LEDs.
Not always! I buy LEDs from a number of different sources and some have the larger internal pin (the "bowl") as the anode.... The side connected to what looks like a bowl is the cathode.
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Really? I have never seen an LED with the "bowl" as the anode. The "bowl" contains the die, and there's a tiny, extremely fine wire connecting to the die from the anode. I don't see how it could work the other way around, I thought the anode always had to be connected to the fine wire....?Not always! I buy LEDs from a number of different sources and some have the larger internal pin (the "bowl") as the anode.
by Duane Benson
by Duane Benson
by Jake Hertz