Hey everyone I have a hobby for making electronic things but have know education in the area.
I want to take on a more seriouse project soon which involves 2 really bright leds , a switch and a 9 volt battery.
Can you tell me what type of leds specs I need to look for when buying? I prefer the colours blue or green.....I need them to be bright because this circut will be on my bike and at night I want it to really stand out.
what is mcd?
viewing angle?
how do I make the led not burn out because of 9 volt battery , can leds handle 9 volt batteries?
Please help and explain in detail
not know, no*
From a 9V source, you can run just about any sort of LED. The blue ones are usually rated for about 3.5V-4.5V or so, while green, yellow, and red are typically more like 1.7-2.1V. White LEDs also exist... sort of. They're usually blue LEDs with a yellow filter, which simulates white.
The LED works like a voltage reference... when you put a current through it, it wants to go to a voltage specific to that LED. In order to prevent the LED from basically fighting against the voltage applied, you need to put a resistor in series with the LED. This will also effectively set the current for the system. More on that in a bit.
MCD = millicandelas... it's a rating of brightness. One candela is supposedly the brightness of one standardized candle, one MCD is 1/1000th the brightness of a candle. Viewing angle is basically indicating the spread of the LED. Most LEDs have lenses molded into their housings,,, the light can be tightly focused, or spread wide.
To ensure you don't damage the LED, you'll need to add a resistor, as mentioned. You'll need to do a little mathematics to calculate just what value, but it's pretty easy. Measure current in Amps or Milliamps (1/1000th of an amp), voltage in volts, and the resistor value in ohms. Ohms law states for any circuit, E = I * R (voltage (volts) = current (amps) * resistance (ohms)).
So, you have a 9V battery. Let's assume you got the 2600mcd blue LED from Radio Shack (p/n 276-316). That LEDs would like 3.7V to 4.5V to it, and it can take a maximum current of 20mA (0.02A). So worst case, you are dropping 5.3V at 20mA in the resistor, 5.3V / 0.02A = 265 ohms. Radio shack sells a 330 ohm resistor, 271-1315, which will work.
Keep in mind that an LED, being a diode, is a polarized device... it only turns on when the anode is connected to + and the cathode to -... this should be indicated on the package. The resistor can go on the anode or cathode, it doesn't matter.
If you want more than one LED, you can actually put two in series from the +9V battery, though you'll need a much smaller resistor. I found a web page that illustrates some of this: http://www.kpsec.freeuk.com/components/led.htm
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