rickpbush:
Hi, I'd like to build a little circuit board with about 5 or 6 leds on it.Each led would be driven from it's own pin on the arduino.
I'd like to supply the power to light the leds from an external power supply so I'm guessing I'll need to use transistors to switch the power.
If the LEDs are 20mA then you don't need the transistors, a resistor will do.
rickpbush:
Seeing as I have 5 or 6 leds, I thought rather than using 5 or 6 separate transistors on my little board it would be nice if I could find a single chip which contains the transistors.
There's lots of LED driver chips available, the right one depends on what you're trying to do, eg. do you need brightness control?
rickpbush:
Please could someone tell me if such a chip exists and if so what is it called ? If I can find out what I need to buy I can ebay it.
TPIC6B595 will give you switching but you still need a resistor for every LEDs.
TLC5940, TLC5916, etc. will regulate the current so you don't need a resistor, just the chip.
rickpbush:
The leds will be 5v leds
That's unlikely. Usually they're 3.6 or 2.2V.