ok so i used an online led calculator to workout what resister i would need to run a single blue smd led off a pc power supply using the 5v. iv read that these online led calculators can be wrong so thought i would ask.

will this resister work (100 ohms)
http://www.ebay.co.uk/itm/300778913069?var=600057335107&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

on one of these leds
http://www.ebay.co.uk/itm/261119055582?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

connected like this

any help will be much appreciated thanks

 

100Ω should give a nominal 18mA at 5V which should be fine for that LED.

 

thank you very much for your reply and help does it matter which side of the resister is on the led ?

 

No. Resistors don't have a polarity preference.

 

thanks. sorry im kinda new but learning am i right in thinking. if the led is too bright for me can i simply add another resister so thats 2 100ohms resisters connected in series ?

 

thanks. sorry im kinda new but learning am i right in thinking. if the led is too bright for me can i simply add another resister so thats 2 100ohms resisters connected in series ?

Yes, you can add additional resistors in series, but don't short out the 100Ω resistor, or your LED will go "poof." For fun, you might want to add a potentiometer (say 5k) in series with the 100Ω. Then, by adjusting the pot, you can dim the LED.

 

cool! thankyou very much im having some pcb's made so just wanted to be 100% sure i have everything correct as its costing me £14 ($22) for 3 boards made that are 9cm long 2cm wide. i personally think that expensive.