Help a newbie buy resistors

Hi there, I'm creating a simple circuit project for my students, though I don't know the first thing about electronics, so I foolishly bought tons of LEDS and 9V clips without the resistors - Doh!

But now that I know I needs resistors, I'm not sure which type of resistors I need. A list like this is quite daunting to choose from. The LEDs I'm using need 1w resistors (I think...). Please feel free to ask my any questions or hand out other advice. Thanks!


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blkhawk5 years ago
A LED Calculator wizard could help you find the right resistor for your project. If your circuit has more than one LED, there is another wizard that could help you also.
doncrush5 years ago
Maybe take a look at whats in some of the kits? Makershed or Radio Shack have some getting started kits for Arduino and they have resistors in there.
quatch5 years ago
I suppose I can answer what you asked as well.

use a site like this: to figure out what value resistor you want. Buy enough.

9v is probably a little high to drive most LEDs, esp normal red ones with a low forward voltage (~2, although some white or NIR may be up around 4), so you'll have a larger dissipation in the resistor, and might need more than 1/4W resistors.
LanceMakes (author)  quatch5 years ago
Yes, I think you're right - I'm going to use a smaller button cell battery instead
the caveat of those is low total capacity. A pair of AAs will last much longer.

I should mention that 9V are really irritating batteries, I spent a few days trying to figure out why I couldn't run my project on one, even though the voltage was right. A 9V can give a peak current of ~24mA (As I recall. Check the docs), and only has ~250mAh capacity.
Dr. D5 years ago
Wikiversity has a nice little guide that'll teach you to read the code of colored stripes resistors, if you don't know how:
LanceMakes (author)  Dr. D5 years ago
Thanks! That helps considerably
quatch5 years ago
I've done it two ways so far. in a pinch, I grabbed a bag of mixed, unsorted resistors from radioshack. it had 2 of each value for a decently wide range, but it is a royal pain to find the one you want. I think it was about 7$

Then, I ordered 20 of each value of the E6 series (see (used the 20% values, but of 5% carbon film) from a random shop in china (tayada). They were cheap, and came in a few weeks. As a bonus they are in little baggies. That'll give me a close-enough resistor for just about any random project I go on, and I can order a specific one and wait if I need it. From them, a huge pile of LEDs (several hundred), transistors and resistors was ~30$.