# LED Array

#### mctoys

Aug 30, 2011
3
Hi All

I have a probably rather embarrassingly simple circuit question which I would like to ask. I am considering building some LED clusters to use as indicators, side lights and brake lights on my motorbike engined kit car project and would like to test a simple 9 LED array to test the brightness and effectiveness.

I have based my circuit on using three sets of three LEDs in series using a 220 ohm resistor and 12v supply. I think these values are ok, but I want to build it on veroboard and am unsure whether I need to use one resistor between the voltage and the three series circuits or whether each one needs it's own resistor. I have sketched up a quick diagram of the two options I am considering. The orange strips are resistors, the black strips are connecting wires and the circles are LEDs.

Can anyone give me their advice as to which circuit will work best or if I've completely screwed up!

Many Thanks
Dan

#### Resqueline

Jul 31, 2009
2,848
The 2nd circuit is definitely the way to go (except you don't want to break the 0V strip).

#### davelectronic

Dec 13, 2010
1,087
Hi there mctoys.
I would use one resistor per 3 led's in series, and calculate the current for three of the led's depending on there current rating and forward voltage for your resistors, others might do it different, any other members do it other than this way ? Dave.

#### mctoys

Aug 30, 2011
3
Brilliant, thank you! Yes of course, simple mistake on the drawing!

#### mctoys

Aug 30, 2011
3
Hi Dave

Yeah, that's what I've got going on with diagram 2. The forward voltage is listed as 1.8-3.2v so I have done my sums based on 2.4v - does that sound sensible to you?

Thanks
Dan

#### Resqueline

Jul 31, 2009
2,848
Depending on the color (red & orange I guess?), yes, but if you have the LED's in hand it'd be best to test them for Vf at the intended current level(s).

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Yeah, do your calculations based on 2.4V, and then measure the actual current/voltage and make an adjustment as is required.

You only need a single resistor per string of three LEDs, and whilst you could string more together for the voltage you have, you have chosen a good compromise based on the quite variable voltage you get on a car 12V system.

There is a sticky thread here which has links to calculators for resistor values which may be of assistance. If you look at that you'll also see verification that your second layout is preferred (and why).

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