White, Blue, Red leds on one circuit.

raypalmer · Post by **raypalmer** » Tue Jan 31, 2012 11:10 pm

Can't figure out how. They're all 20mA 5mm LED's.

I think i'll need about 20 white, 3 blue, 3 red. So... over 500mA PS. Say a 1A 9V wall wart.

What's the circuit look like? Nothing's blinking or strobing, I want them all at full brightness. Just need the resistor layout. Anyone who can point me to required reading or walk me through it a bit would really help me out.

en'til Zog · Post by **en'til Zog** » Wed Feb 01, 2012 12:02 am

All 20 mA, yes. But probably different voltages.

At least the RED LEDs are probably 2.4 VOLT, while the BLUE and WHITE ones are probably 3.4 VOLT. That will affect your resistor selection.

Sparky · Post by **Sparky** » Fri Feb 03, 2012 10:08 pm

remember if you daisy chain the LEDs the current is not additive, the voltage is. So if you have a chain of leds and they all want 20 mA, they must all want that cause the current cannot change in the loop, then add the voltage and thats the voltage you will need for that chain, Current is 20mA.

you must find out for sure what the voltages are for each LED type before we can come up with the most efficient configuration. Remember any resistor used is consuming power from you power supply that is wasted, usually as waste heat.

Doomgiver · Post by **Doomgiver** » Thu Feb 09, 2012 4:46 am

Here is your list:

10x: 2x LED(white) + 150Ohm Resistor
1x: 3x LED(red) + 180Ohm Resistor
1x: 2x LED(blue) + 150Ohm Resistor
1x: 1x LED(blue) + 390Ohm Resistor

Total current is about 250-260mA.

Sparky · Post by **Sparky** » Thu Feb 09, 2012 11:55 am

i don't know how you can calculate resistor values without knowing the LED's forward working voltage and their forward working current. You don't want to guess on these since you will either under drive the LED or overdrive them.

He want's full brightness so that means getting the exact requirements of the LEDs and building the circuit to drive right up to those limits.

raypalmer · Post by **raypalmer** » Sat Feb 11, 2012 4:29 pm

Yeah I dunno. I was having a bad brain day, for some reason I forgot how to use the breadboard correctly and my parallel circuits weren't right. Caused the different colours to not work on the same circuit.

Essentially I was being stupid when I asked this question, I have to cop to that.

Once I realized I had my head in m'bum I re-wired correctly, figured voltage and current and got it all sorted.

Thanks for the replies everyone.

en'til Zog · Post by **en'til Zog** » Sat Feb 11, 2012 10:34 pm

YAYAYAY!

Doomgiver · Post by **Doomgiver** » Tue Feb 14, 2012 10:45 am

Sparky wrote:i don't know how you can calculate resistor values without knowing the LED's forward working voltage and their forward working current. You don't want to guess on these since you will either under drive the LED or overdrive them.

He want's full brightness so that means getting the exact requirements of the LEDs and building the circuit to drive right up to those limits.

That's not so complicate. Red, Yellow and Green Led have 2,0V (+/-0,2V) and 20mA current. White and Blue Led use 3,4-3,7V and also 20mA (sometimes 30mA, but that's uninteresting).
Most LED have full brightness by 15-20mA, also white and blue Leds. So, it is often not useful, to work with maximum ratings.