EL EEE DEEZ Resistor and Circuts

Moar on Different types of circuts for LEDS and where to get the shit you need for cheap.

 So, im gonna give a quick rundown on an led circut and how certain types of LEDS have different energy needs and how that results in needing resistors. 


First off, lets say I want to make a small circut. For examples sake, lets say I want to use 3 leds. I bought mine last semester from an online store, called Super Bright LEDS, obviously enough. There are alot of different suppliers but most require you to buy in bulk, at least $99 worth, and are from China and India. The LEDS are cheaper in theory, but unless you want your own version of the room from Invisible Man, I see no purpose in this.




Back to LEDs: so I'm going to make a parallel circut, because thats what im comfortable with. You can wire LEDS in parallel or in series. This website, The LED Calculator, helps out greatly with finding out the configurations. Note: if you want to use different colored LEDS you have to wire in series, because each different LED has dif energy requirements. Or, you have to have a resistor for each LED to make all of the forward voltages low enough in a parallel circut. The specs for each LED are on the manufacturers website.
For example, if I am hooking up my blue LED to a 9 volt battery in a simple parallel circut I would have to stay between 4.0 and 3.5 volts of forward voltage, or the electricity going into the LED. Then, The LED Calculator wants to know the forward current, which is alot more flexible. The specs on my LED say that the best would be 30 milliamps (mA), but the chart below shows that the LED shouldn't blow out before hitting 45 mA. The chart also shows that I can send as little as 5 mA through my LED and that it will still light up, but only barely. A typical spec page


The results: I need one 220 Ohm resistor that is 1/4 watts! 

Now, you may not be able to find the resistor that the page asks for. If thats the case, you can tweak the forward voltage and current until it spits out a resistor that is easier to find, or cheaper. Really, if you pay more than around two dollars or so for it you should try some other combinations. Most resistors cost cents.  The place where I got mine from is called Parts Express. I recommend getting the recommended resistor and one the next ohm caliber down that the store has, so if one turns out too strong in practice you can just switch it out with a weaker one.

Ok, so on to our 3 LED circut: 

Supply Voltage: 9 volts

LED Forward Voltage: 3.5 volts

LED Forward Current: 35 milliamps

Resistor: 56 Ohm 1 watt resistor

Okay, this is how much the supplies for the circut will cost you:

Batteries: $3

LEDs: 72 cents each, $2.16 total

Resistor: 69 cents 

Thats $5.85 total. Fun!