You could buy a power supply from minispotlight, that way you aren't draining batteries. It seems to me they were like $15.00 or so. That just covers your source though, you still need them resistors.
BTW: technically you could power your 8 LEDs with fewer resistors, but this way you can have as few or as many LED/resistor pairs as you want without having to recalculate anything.
Okay, so here's what we know about your LEDs:
Forward Current - 20mA
Forward Voltage - 2.2
If you use a 9v power supply or battery and the LEDs are dropping 2.2v of that, then it means we need the resistor to drop 6.8v (9-2.2). We now know the voltage across the resistor and the current going through it (20ma or .02 amps, same as the LEDs), so we can use Ohm's law.
6.8v / .02A = 340 ohms
The next-highest standard value resistor is 390 ohms, so that's what you'd want to use (get 1/4 watt; 1/8 watt isn't big enough).
Ideally you would have a separate resistor for each LED. 9v will drive them all just fine, just make sure to choose the appropriate value resistors (if you post the voltage rating of your LEDs I can help you with that).
Ideally you would have a separate resistor for each LED. 9v will drive them all just fine, just make sure to choose the appropriate value resistors (if you post the voltage rating of your LEDs I can help you with that).
Also note that since you are drawing 160ma total you will probably get just shy of 2 hours out of a 9v battery. You may want to use a wall-wart instead.
Anyway, here's a quick schematic I drew of how you can hook up your 8 LEDs:
Young man, I suggest you take some basic night classes in electricity and electronics. Otherwise, you are going to be dangerous around components and circuits.
( In parallel, 18 volts is going to burn out a lot of LEDs)
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