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/diy/ - Do It Yourself

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392066 No.392066 [Reply] [Original]

So I'm trying to get into circuits, and I've tried all three of these setups (with a fresh LED every time.)

I haven't seen even a blink of light yet. Any advice on what I could be doing wrong?
Thanks in advance.

>> No.392077

Sure you have it wired with correct polarity? It is a diode after all. I've seen some LEDs where the shorter leg indicated the + side, which is not normal. Try flipping the LED around.

>> No.392083
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392083

28ma
2.6V pass
not sure, but I'm gonna assume that means
28mA max current with a forward voltage drop of 2.6V

The first one won't light because 1.5V does not overcome the 2.6 Volt LED voltage "barrier"

Second:
3 Volts applied
2.6 Volts "dropped" by the LED
This leaves 0.4 Volts to be dropped by the resister. (.4+ 2.6 = 3)

The current through the resister can be found using the formula
I = V/R = 0.4V/200ohms = .002 = 2mA
The current through the LED will be the same.
I don't think this will be enough to see the light. maybe in a dark room.

The 3rd one should light but is not a good design because of no current limiting resister.
Excessive current could result. I've seen people say that it worked fine like that but I wouldn't do it.(at least for long)

The polarity of the LED has to be right. If you look inside the LED you'll see one big and one small piece. the big one goes toward the -negative side of the battery. Some also have a flat part at the biggest round part of the LED but I don't remember if it goes to + or -

Also: Those are light bulbs in your schematic, not LED's