resistor question

[roughwater71]

tuxedocartman,
you should stick with elvis inpersonations,LOL

[TuxedoCartman]

tuxedocartman,
you should stick with elvis inpersonations,LOL

Fine, but when I build my next saber out of nothing but cheap Rolexes and free iPads, I don't want to hear how jealous you are! ^_^

[cshaley]

Rather than starting a new thread (since this one is pretty recent), I thought I'd tack on my question here...

I've been reading through the PC 2.0 manual, trying to calculate the resistor value to use for a green accent LED (from TCSS). The supply from the board to the accent pads is 3.3V, and the LED is rated at 2.2V with 25mA. So if I'm doing the math right, (3.3V-2.2V)/.025A = 44ohm. Or, if I wanted to run the LED with less current (the manual advices nothing above 18mA), 1.1V/.018A = 61ohm.

Does that sound right? I ask because I can't find a resistor with anything close to those values listed in the shop. They jump from about 18 to 82 ohms, with nothing in between. I'd be fine making a trip to Radio shack, I just wanna make sure I'm picking up the correct resistors.

[Ari-Jaq Xulden]

44 is correct. The closest you will be able to find will be a 47 ohm. Which is what you need.

[cshaley]

Sounds good... A quick search on radioshack reveals a number of 47ohm resistors, which vary by wattage rating. Am i trying to match that as close as possible to the LED? (for example, would a 47ohm 1/4w resistor be preferable to a 47ohm 1w resistor, or am i looking for something else entirely?)

Thanks again, in advance. I'm trying to be as self-reliant a noob as possible, but some of the finer points in electronics escape my comprehension.

[Ari-Jaq Xulden]

Actually a 1/8w rated is the recommended for that particular led. However the 1/4 watt will be fine, If your just planning on bridging the resistor pads on the PC.You will not be able to use that resistor on the pads of the PC as they were so designed, that would require an smd resistor. Please refer to the manual.

[cshaley]

So, to be clear, if I want to install it on the board I would need a 47 ohm 1/8w SMD resistor?

And, unless I'm missing something, none of this information can be found in the manual. I've been reading it extensively, but cannot find the answers to any of these questions about resistors. How to install them, yes. How to calculate ohm value, yes (which I did in the above post). But nothing about the Amp rating or what types of resistors to use. I'm not asking anyone to do my work for me, just politely looking for additional clarification.

[Xanatos1986]

If you want the resistor on the board use a smd resistor... if not use the resistor either on the negative wire or positive wire. I prefer positive wire.

[cshaley]

I had no idea they were interchangeable. I thought resistors could only be used on the positive wire. Is your preference one of convenience, or does it somehow change the intensity of the light to use on one or the other?

Also, where does one find SMD resistors? These are the only two I could find on RadioShack's website that said anything about "surface mount..." option 1 option2

EDIT: I realize now that my search for SMD resistors is redundant, as the pads come "pre-bridged" on the PC2.0, and I'd be forced to use an external resistor anyway. So, disregard that portion of my query...

[Silver Serpent]

Yep, you can put the resistor on either wire. It makes no difference to the circuit. Most people just pick one side and stick with it for consistency.

You're not going to find SMD resistors at Radio Shack. There are electronics sites out there if you Google for them. (I can't provide links here, since they sell products that compete with TCSS)

Really excellent electronics people (i.e. people who aren't me) will consider un-bridging the pads on the PC, and adding SMD resistors. I'd just stick with putting them on the neg or pos line.